@article{23, author = "Haidemenopoulos, G.N.", abstract = "A 1.7kW CO2 laser was used for the study of bead-on-plate welds in D36 ship steel. The effect of welding heat input and focal point position on weld geometrical features and microstructure was determined. It was found that weld penetration as well as the width of weld pool and heat-affected-zone (HAZ) increase with heat input. Microstructure and hardness in the weld pool, Partial fusion zone and HAZ are also influenced by heat input. As the heat input is increased, the associated cooling rate is decreased, resulting in the formation of softer microstructures. Simple analytical models describing heat flow during welding were used to calculate the above mentioned geometrical features. The agreement between the calculated and experimentally determined weld penetration, as well as weld pool width, is sufficiently good and depends on weld heat input. The optimum experimental conditions defined from the bendon-plate study were applied to Laser welding of butt joints in 4mm D36 steel.", journal = "Tech. Chron. Sci.J. TCG", number = "1-2", pages = "63-71", title = "{A} {M}acro and {M}icro-structural {S}tudy of {L}aser {W}elds in {D}36 {S}hip {S}teel", year = "1998", } @article{44, author = ", ", abstract = "Despite the critical effect of heat-treatment, and in particular of the isothermal bainitic treatment stage, on the amount and stability of retained austenite in the microstructure of low-alloy TRIP-assisted steels, determination of optimum heat-treatment conditions is still largely empirical and experiment-dependent. This work proposes a method by which it is possible to calculate the vol. fraction of retained austenite in the microstructure as a function of intercritical annealing temperature and isothermal bainilic treatment temperature and holding time. The method assumes diffusionless lengthening of bainitic ferrite (αB) plates in austenite (γ), and subsequent thickness-wise C rejection from the αB plates to the adjacent γ layers. The relative thickness of αB plates and adjacent γ layers is determined by the To line of the transforming system at any given bainitic transformation temperature. The C-concentration profiles in γ are calculated with respect to a local time-scale, referring to any random section of any random αB plate. Determination of the variation of C-concentration profiles with local time in γ, together with the use of a simple austenite-retention criterion, allows the calculation of vol. fraction retained austenite (γR) as a function of transformation temperature and local time. Transition from local (calculation) time to actual heat treatment time is performed by introducing a time-scale factor, which depends on transformation temperature and initial C-content of αB. The calculated behaviour of vol. fraction γR vs. bainitic holding time conforms to the well established, experimentally observed one: vol. fraction γR initially increases with holding time, reaches a maximum and decreases at longer holding times. According to calculated results, the decrease is attributed to the gradual homogenization of C inside the γ layers, which leads to inadequate stabilization and transformation of γ to martensite on quenching. As regards quantitative comparison with available experimental data, calculations show reasonable agreement. Certain refinements of the method, which are underway, are reported, in order to further improve quantitative results. Nevertheless, the method in its present form provides a calculational tool, by which the effect of different heat-treatment conditions or steel compositions can be examined and compared to each other, which can be a useful step towards optimizing alloy compositions and heat-treating processes.", journal = "Steel Research International", number = "3", pages = "210-217", title = "{A} {M}ethod for the {C}alculation of {R}etained {A}ustenite {E}volution during {H}eat-{T}reatment of {L}ow-{A}lloy {TRIP}-assisted {S}teels", volume = "77", year = "2006", } @article{56, author = "Lambrakos, S.G. and Zervaki, Anna and Haidemenopoulos, G.N.", abstract = "A numerical method for inverse thermal analysis of steady-state energy deposition in plate structures is constructed according to the general physical characteristics of energy deposition within a volume of material from a beam energy source. This numerical method represents implementation of a general methodology using basis functions that was introduced previously. The formal structure of the numerical method presented follows from a specific definition of the inverse heat transfer problem, which is well posed for inverse analysis of heat deposition processes. This definition is based on the assumption of the availability of information concerning spatially distributed boundary and constraint values. This information would be obtained in principle from both experimental measurements obtained in the laboratory, as well as numerical simulations performed using models having been constructed using basic theory. Experimental measurements include solidification cross sections, thermocouple measurements, and microstructural changes.", doi = "10.1007/s11665-011-9963-7", journal = "Journal of Materials Engineering and Performance", number = "2", pages = "180-190", title = "{A} {N}umerical {M}ethod for {I}nverse {T}hermal {A}nalysis of {S}teady-{S}tate {E}nergy {D}eposition in {P}late {S}tructures", url = "http://link.springer.com/article/10.1007/s11665-011-9963-7?null", volume = "21", year = "2012", } @article{48, author = ", and Haidemenopoulos, G.N.", abstract = "A Semi-Empirical Model for the evolution of Retained Austenite via Bainitic Trans-formation in Multiphase TRIP Steels, Steel Research Int., 79 (2008) No.11, pp.875-884 Abstract Download ", issn = "1611-3683", journal = "Steel Research International", number = "11", title = "{A} {S}emi-{E}mpirical {M}odel for the evolution of {R}etained {A}ustenite via {B}ainitic {T}rans-formation in {M}ultiphase {TRIP} {S}teels", volume = "79", year = "2008", } @article{1, author = "Mica Grujicic and Haidemenopoulos, G.N.", abstract = "It is demonstrated that the ThermoCalc computer program and database can be used for calculation of phase paraequilibrium provided proper modifications of phase descriptions have been made. This procedure has been used to analyze precipitation of M2C carbides from a "paraequilibrium" two-phase ferrite/cementite mixture in standard and series of modified AF1410 steels. It is found that from the standpoint of achieving fine dispersion of M2C phase and thus improved strength properties, it is beneficial to make a complete substitution of chromium with molybdenum in steels of this class.", doi = "10.1016/0364-5916(88)90002-8", journal = "CALPHAD", month = "July-August", number = "3", pages = "219-224", title = "{A} treatment of paraequilibrium thermodynamics in {AF}1410 steel using the thermocalc software and database", url = "http://dx.doi.org/10.1016/0364-5916(88)90002-8", volume = "12", year = "1988", } @article{85, author = "G. N. Haidemenopoulos and K. Polychronopoulou and A. D. Zervaki and H. Kamoutsi and S. I. Alkhoori and S. Jaffar and P. Cho and H. Mavros", abstract = "An investigation of aging phenomena during creep exposure has been conducted for HP-Nb cast reformer tubes for several exposure conditions. Aging was manifested by carbide precipitation, carbide coarsening, and carbide transformation. The transformation of primary M7C3 to the more stable M23C6 carbide takes place at high exposure temperature (910 {\^A}°C and above). The primary MC carbides transform to the Ni-Nb silicide or G-phase during creep exposure. The presence of Ti in the steel prevented the transformation of MC carbides to the G-phase. Morphological changes like needle to globular transitions, rounding of carbide edges, and carbide coarsening take place during creep exposure. The room-temperature tensile elongation and ultimate tensile strength are significantly reduced during creep exposure. The above aging phenomena are precursors to creep damage.", doi = "10.3390/met9070800", issn = "2075-4701", journal = "Metals", number = "7", title = "{A}ging {P}henomena during {I}n-{S}ervice {C}reep {E}xposure of {H}eat-{R}esistant {S}teels", url = "https://www.mdpi.com/2075-4701/9/7/800", volume = "9", year = "2019", } @article{75, author = "John S. Aristeidakis and Haidemenopoulos, G.N.", abstract = "A new alloy design methodology is presented for the identification of alloy compositions, which exhibit process windows (PWs) satisfying specific design objectives and optimized for overall performance. The methodology is applied to the design of medium-Mn steels containing Al and/or Ni. By implementing computational alloy thermodynamics, a large composition space was investigated systematically to map the fraction and stability of retained austenite as a function of intercritical annealing temperature. Alloys exhibiting PWs, i.e., an intercritical annealing range, which when applied satisfies the given design objectives, were identified. A multi-objective optimization method, involving Pareto optimality, was then applied to identify a list of optimum alloy compositions, which maximized retained austenite amount and stability, as well as intercritical annealing temperature, while minimized overall alloy content. A heuristic approach was finally employed in order to rank the optimum alloys. The methodology provided a final short list of alloy compositions and associated PWs ranked according to their overall performance. The proposed methodology could be the first step in the process of computational alloy design of medium-Mn steels or other alloy systems.", doi = "https://doi.org/10.1007/s11661-017-4010-4", issn = "1543-1940", journal = "Metallurgical and Materials Transactions A", keywords = "Austenite, Cementite, Pareto Optimal Solution, Intercritical Annealing, Alloy Design", month = "May", number = "5", pages = "2584–2602", title = "{A}lloy {D}esign {B}ased on {C}omputational {T}hermodynamics and {M}ulti-objective {O}ptimization: {T}he {C}ase of {M}edium-{M}n {S}teels", url = "https://rdcu.be/bWZxa", volume = "48", year = "2017", } @inbook{2002, author = "J.R. Kissell and S. Pantelakis and Haidemenopoulos, G.N.", editor = " J.K. Wessel", isbn = "0-471-45475-3", pages = "321-463", publisher = "Wiley Interscience, Hoboken, New Jersey, USA", series = "The Handbook of Advanced Materials", title = "{A}luminum and {A}luminum {A}lloys, {C}hapter 9 in {T}he {H}andbook of {A}dvanced {M}aterials, ed. {J}.{K}. {W}essel,", year = "2004", } @article{49, author = " Zervaki, Anna and Haidemenopoulos, G.N. and S.G. Lambrakos", abstract = "The concept of constructing parameter spaces for process control and the prediction of properties within the heat affected zone (HAZ) of welds using inverse modeling is examined. These parameter spaces can be, in principle, either independent or a function of weld process conditions. The construction of these parameter spaces consists of two procedures. One procedure entails calculation of a parameterized set of temperature histories using inverse heat transfer analysis of the heat deposition occurring during welding. The other procedure entails correlating these temperature histories with either a specific process control parameter or physical property of the weld that is measurable. Two quantitative case study analyses based on inverse modeling are presented. One analysis examines the calculation of temperature histories as a function of process control parameters. For this case, the specific process control parameter adopted as prototypical is the electron beam focal point. Another analysis compares some general characteristics of inverse and direct modeling with respect to the prediction of properties of the HAZ for deep penetration welding of aluminum alloys. For this case, the specific property adopted as prototypical is hardness. This study provides a foundation for an examination of the feasibility of constructing a parameter space for the prediction of weld properties using weld cross-section measurements that are independent of weld process conditions. Abstract Download", doi = "10.1007/s11665-007-9145-9", journal = "Journal of Materials Engineering and Performance", number = "3", pages = "402-410", title = "{A}nalysis of {H}eat-{A}ffected {Z}one in {W}elded {A}luminium {A}lloys {U}sing {I}nverse and {D}irect {M}odelling", url = "http://www.springerlink.com/content/j52gr60553x08g44/", volume = "17", year = "2008", } @article{7, author = "A.G. Mamalis and Haidemenopoulos, G.N.", abstract = "Transformation plasticity, the macroscopic plastic associated with phase transformations under stress, has allowed the achievement of improved mechanical properties in a wide range of materials. In metastable fully-austenitic steels, transformation plasticity is responsible for the significant enhancement of ductility and toughness. The ultra-high-strength martensitic steels toughness enhancement of the order of 40% is attributable to the transformation of precipitated austenite, a phenomenon called dispersed-phase transformation toughening. These concepts are explored further towards the development of triple-phase microstructures in low-alloy steels where the transformation plasticity of dispersed austenite leads to the enhanced stretch-formability required for automotive applications.", doi = "10.1016/0924-0136(92)90347-U", journal = "Journal of Materials Processing Technology", month = "March ", number = "2", pages = "211-230", title = "{A}spects of {D}uctility, {T}oughness and {F}ormability of {S}teel {S}heet in {R}elation to {T}ransformation {P}lasticity", url = "http://dx.doi.org/10.1016/0924-0136(92)90347-U", volume = "30", year = "1992", } @article{69, author = "Tzini, M.I.T. and Sarafoglou, P.I and Stieben, A. and Haidemenopoulos, G.N. and Bleck, W.", journal = " Steel Research International", number = "in press a", title = "{A}ustenite evolution and solute partitioning during thermal cycling in the intercritical range of a medium-{M}n steel", year = "2016", } @article{16, author = "Haidemenopoulos, G.N.", journal = "Steel Research", number = "3", pages = "93-99", title = "{A}ustenite {S}tabilization from {D}irect {C}ementite {C}onversion in {L}ow-{A}lloy {S}teels", volume = "67", year = "1996", } @article{66, author = "Samaras, G.F. and Haidemenopoulos, G.N.", journal = "Engineering Failure Analysis", pages = "29-36", title = "{C}arburization of high-temperature steels: {A} simulation-based ranking of carburization resistance", volume = "51", year = "2015", } @inbook{2007, author = "G.N. Haidemenopoulos and A. Katsamas", title = "{C}arburizing: {L}aser {B}eam, {E}ncyclopedia of {I}ron, {S}teel and {T}heir {A}lloys, {R}afael {C}olas and {G}eorge {T}otten (editors), {T}aylor and {F}rancis, {N}ew {Y}ork, {USA}, p.631-642", year = "2016", } @article{57, author = " Zervaki, Anna and Vriami,D.P. and Haidemenopoulos, G.N. and Lambrakos, S.G.", abstract = "Case study inverse thermal analyses of A12139 laser welds are presented. These analyses employ a numerical methodology that is in terms of analytic and numerical basis functions for inverse thermal analysis of steady state energy deposition in plate structures. The results of the case studies presented provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations and their associated software implementations. In addition, these weld temperature histories will be useful for construction of numerical basis functions that can be adopted for inverse analysis of welds corresponding to other process parameters or welding processes whose process conditions are within similar regimes. ", doi = "10.1007/s11665-011-9968-2", journal = "Materials Engineering and Performance", keywords = "aluminum, modeling processes, welding ", number = "6", pages = "777-785", title = "{C}ase {S}tudy: {I}nverse thermal analysis of {A}l 2139 {L}aser {W}elds", url = "http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012JMEP...21..777Z{\&}link_type=EJOURNAL", volume = "21", year = "2012", } @article{58, author = " Zervaki, Anna and Vriami, D.P. and Haidemenopoulos, G.N. and Lambrakos, S.G.", abstract = "In this article, case-study inverse thermal analyses of Al2198 laser welds are presented. These analyses employ a numerical methodology, that is, in terms of analytic and numerical basis functions for inverse thermal analysis of steady-state energy deposition in plate structures. The results of the case studies presented provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations and their associated software implementations. In addition, these weld temperature histories can be used for construction of numerical basis functions that can be adopted for inverse analysis of welds corresponding to other process parameters or welding processes whose process conditions are within similar regimes.", doi = "10.1007/s11665-011-9967-3", journal = "Journal of Materials Engineering and Performance", number = "4", pages = "471-480", title = "{C}ase {S}tudy: {I}nverse thermal analysis of {A}l 2198 {L}aser {W}elds", url = "http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012JMEP...21..471Z{\&}link_type=EJOURNAL", volume = "21", year = "2012", } @article{91, author = "A. D. Zervaki and V. Stergiou and S. G. Lambrakos", abstract = "Case study inverse thermal analyses of A12139 and Al2198 electron beam welds are presented. These analyses represent a continuation of previous studies using laser beam welds, but provide accessibility to different regions of the parameter space for temperature histories than achievable using laser beams. For these analyses, a numerical methodology is employed, which is in terms of analytic functions for inverse thermal analysis of steady-state energy deposition in plate structures. The results of the case studies presented provide parametric representations of weld temperature histories, which can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations and their associated software implementations. In addition, these weld temperature histories can be used for construction of numerical basis functions that can be adopted for inverse analysis of welds corresponding to other process parameters or welding processes process conditions of which are within similar regimes.", day = "01", doi = "10.1007/s11665-013-0612-1", issn = "1544-1024", journal = "Journal of Materials Engineering and Performance", month = "Nov", number = "11", pages = "3175--3181", title = "{C}ase-{S}tudy {I}nverse {T}hermal {A}nalyses of {A}l2139 and {A}l2198 {E}lectron {B}eam {W}elds", url = "https://doi.org/10.1007/s11665-013-0612-1", volume = "22", year = "2013", } @article{30, author = "E. Charitidou and G. Papapolymerou and Haidemenopoulos, G.N. and N. Hasiotis and V. Bontozoglou", abstract = "E. Charitidoua, G. Papapolymeroua, G. N. Haidemenopoulosa, N. Hasiotisa and V. Bontozogloua", journal = "Scripta Materialia", keywords = "Aluminium; Hydrogen; Trapping states", number = "12", pages = "1327-1332", title = "{C}haracterization of trapped hydrogen in exfoliation corroded aluminum alloy 2024", url = "http://dx.doi.org/10.1016/S1359-6462(99)00292-4", volume = "41", year = "1999", } @article{46, author = " Zervaki, Anna and Haidemenopoulos, G.N.", abstract = "Laser beam welding (LBW) has become common practice in the production lines of several industrial sectors including the electronics, domestic appliances, and automotive industries. The advantages of LBW over conventional fusion welding processes (mainly GMAW and GTAW) is the lower welding heat input and smaller weld pool and HAZ dimensions, which are associated with lower residual stresses and distortion. In addition to the general problems encountered during the application of LBW on aluminumalloys (high reflectivity, porosity, loss of alloying elements), the most important problem, which concerns the heat treatable alloys, is the softening of the HAZ due to the dissolution and coarsening of the strengthening precipitates. The main objective of the present work is the simulation of the microstructural evolution in the HAZ in order to predict the hardness drop of the HAZ as a function of welding conditions. Models for the numerical simulation of precipitation, dissolution, and coarsening of β-Mg2Si phase were developed and solved with the use of the computational thermodynamics and kinetics software DICTRA. In this way the volume fraction and average precipitate size were calculated for several types of weld thermal cycles, under extremely nonisothermal conditions. Calculated hardness profiles in the HAZ are in good agreement with the experimental values. The above results point to the conclusion that it is possible to simulate the microstructure evolution and hardness in the HAZ of aluminum laser welds, thus opening the way for a more precise control and design of LBW of aluminum alloys.", journal = "Welding Journal", month = "August", pages = "211s-221s", title = "{C}omputational {K}inetics {S}imulation of the {D}issolution and {C}oarsening in the {HAZ} during {L}aser {W}elding of 6061-{T}6 {A}l-alloy", url = "http://www.aws.org/wj/2007/08/", volume = "86", year = "2007", } @article{6, author = "Haidemenopoulos, G.N.", journal = "Mineral Wealth", pages = "41-52", title = "{C}omputer-{A}ided {T}hermodynamics of {A}lloys", volume = "74", year = "1991", } @article{43, author = "I. Papatriantafilloua and M. Agorasa and N. Aravas and Haidemenopoulos, G.N.", abstract = "A constitutive model that describes the mechanical behavior of steels exhibiting "TRansformation Induced Plasticity" (TRIP) during martensitic transformation is presented. Multiphase TRIP steels are considered as composite materials with a ferritic matrix containing bainite and retained austenite, which gradually transforms into martensite. The effective properties and overall behavior of TRIP steels are determined by using homogenization techniques for non-linear composites. A methodology for the numerical integration of the resulting elastoplastic constitutive equations in the context of the finite element method is developed and the constitutive model is implemented in a general-purpose finite element program. The model is calibrated by using experimental data of uniaxial tension tests in TRIP steels. The problem of necking of a bar in uniaxial tension is studied in detail. The constitutive model is used also for the calculation of "forming limit diagrams" for sheets made of TRIP steels; it is found that the TRIP phenomenon increases the strain at which local necking results from a gradual localization of the strains at an initial thickness imperfection in the sheet.", journal = "Computer Methods in Applied Mechanics and Engineering", month = "15 July", number = "37-40", pages = "5094-5114", title = "{C}onstitutive modeling and finite element methods for {TRIP} steels", url = "http://dx.doi.org/10.1016/j.cma.2005.09.026", volume = "195", year = "2006", } @article{89, author = "Pantelakis Spiros", abstract = "Purpose{\^a}?? The purpose of this paper is to quantify the corrosion damage evolution that has occurred on the aircraft aluminum alloy 2024 after the exposure to Exfoliation Corrosion Test (EXCO) solution. Moreover, the effect of the evolving corrosion damage on the materials mechanical properties has been assessed. The relevance of the corrosion damage induced by the exposure to the laboratory EXCO for linking it to the damage developed after the exposure of the material on several outdoor corrosive environments or in service is discussed. Design/methodology/approach{\^a}?? To induce corrosion damage the EXCO has been used. For the quantification of corrosion damage the metallographic features considered have been pit depth, diameter, pitting density and pit shape. The effect of the evolving corrosion damage on the materials mechanical properties has been assessed by means of tensile tests on pre corroded specimens. Findings{\^a}?? The results have shown that corrosion damage starts from pitting and evolves to exfoliation, after the development of intergranular corrosion. This evolution is expressed by the increase of the depth of attack, as well as through the significant growth of the diameter of the damaged areas. The results of the tensile tests performed on pre corroded material made an appreciable decrease of the materials tensile properties evident. The decrease of the tensile ductility may become dramatic and increases on severity with increasing corrosion exposure time. SEM fractography revealed a quasi-cleavage zone beneath the depth of corrosion attack. Originality/value{\^a}?? The results underline the impact of corrosion damage on the mechanical behavior of the aluminum alloy 2024 T3 and demonstrate the need for further investigation of the corrosion effect on the structural integrity of the material. This work provides an experimental database concerning the quantification of corrosion damage evolution and the loss of material properties due to corrosion.", day = "01", doi = "10.1108/IJSI-03-2014-0010", issn = "1757-9864", month = "Jan", number = "1", pages = "25--46", publisher = "Emerald Group Publishing Limited", title = "{C}orrosion damage evolution of the aircraft aluminum alloy 2024 {T}3", url = "https://doi.org/10.1108/IJSI-03-2014-0010", volume = "7", year = "2016", } @article{55, author = "Papadopoulos, M.P. and Apostolopoulos, C.A. and Zervaki, Anna and Haidemenopoulos, G.N.", abstract = "In a large number of steel reinforced concrete buildings in Greece, spalling of the cement has left the steel reinforcement (rebars) exposed to the atmosphere. This has led to corrosion of the exposed rebars, especially in coastal areas, with questions regarding their remaining load-carrying capacity. This work addresses the problem of corrosion and strength degradation of such exposed rebars. A large number of samples (sections of exposed rebars) were collected from buildings up to 96 years old, and weight loss measurements, tensile testing and fractographic analysis were carried out. Accelerated corrosion testing (salt spray) was performed on new similar grade rebars in order to establish a correlation with the naturally corroded exposed rebars. It was found that exposed rebars suffer from uniform corrosion followed by degradation of mechanical properties. In certain cases the properties were below the minimum threshold required by the international standards. A rough estimate of the correlation factor between natural corrosion of exposed rebars and salt spray corrosion has been derived. This correlation factor could be used, under certain limitations, to estimate the condition, in terms of mechanical property degradation and structural integrity, of coastal buildings with exposed rebars in Greece. ", doi = "http://dx.doi.org/10.1016/j.conbuildmat.2011.03.027", journal = "Construction and Building Materials", number = "8", pages = "3367-3374", title = "{C}orrosion of {E}xposed {R}ebars, {A}ssociated {D}egradation and {C}orrelation with {A}ccelerated {C}orrosion {T}ests", url = "http://www.sciencedirect.com/science/article/pii/S0950061811000730", volume = "25", year = "2011", } @article{71, author = "Haidemenopoulos, G.N. and Kamoutsi, Helen", journal = " Encyclopedia of Aluminium and Aluminum Alloys, George Totten and Ollaf Kessler (editors), Taylor and Francis, New York, USA,", title = "{C}orrosion-induced hydrogen embrittlement in 2014 aluminum alloy", year = "2016", } @article{45, author = " Kamoutsi, Helen and Haidemenopoulos, G.N. and V. Bontozoglou and S. Pantelakis", abstract = "The present paper focuses on the observed corrosion-induced embrittlement of alloy 2024 and tries to answer the key question on whether the observed embrittlement is attributed to hydrogen uptake and trapping in the material. Hydrogen is produced during the corrosion process and is being trapped in distinct energy states, which correspond to different microstructural sites. The formation of a hydrogen-affected zone beneath the corrosion layer is supported by fractographic analysis. Removal of the corrosion layer leads to complete restoration of yield strength but only partial restoration of ductility. Additional heat treatment to release the trapped hydrogen leads only to complete restoration of ductility.", journal = "Corrosion Science", keywords = " Aluminium; AFM; SEM; Exfoliation corrosion; Hydrogen embrittlement; Hydrogen trapping; Fractography", month = "May", number = "5", pages = "1209-1224", title = "{C}orrosion-{I}nduced {H}ydrogen {E}mbrittlement in {A}luminum {A}lloy 2024", url = "http://dx.doi.org/10.1016/j.corsci.2005.05.015", volume = "48", year = "2006", } @inbook{2008, author = "Haidemenopoulos, G.N. and H. Kamoutsi", title = "{C}orrosion-induced {H}ydrogen {E}mbrittlement in {A}luminum {A}lloy 2024, {E}ncyclopedia of {A}luminium and {I}ts {A}lloys, {G}eorge {T}otten and {O}llaf {K}essler (editors), {T}aylor and {F}rancis, {ISBN} 9781466510807, {N}ew {Y}ork, {USA}", year = "2018", } @article{34, author = "Haidemenopoulos, G.N.", abstract = "Severnl important industrial material processes, such as welding and surface treatments with high energy beams, incorporate rapid IhcrIllnJ cycles characteri zed by high henling/cooling rates and sh0l1 dwell limes. COmpUl:llional si mulation of the evolution of microS!illClure under these ex treme condit ions has received rather limited attention. With the advct1\ of modern computntiollal tools regarding alloy thermodynamics and kinetics, it is possible to simulate the progress of diffu siolln l phnse tmnsforrnm ions nnd thus to pred ict microstructurnl development. In the present work, moving boundary diffusion problems hnve been simulnted for two cnses, In the first C,lse the rapid austenitizalion duri ng laser tmnsformotion hordening of n hypoeuteetoid steel was examined. ", journal = "Journal of Alloys and Compounds", keywords = "Rapid austenitization; Computational thermodynamics; Kinetics; Dissolution; Coarsening; Weld thermal cycle", number = "2", pages = "320-307", title = "{C}oupled {T}hermodynamic / {K}inetic {A}nalysis of {D}iffusional {T}ransformations {D}uring {L}aser {H}ardening and {L}aser {W}elding", url = "http://dx.doi.org/10.1016/S0925-8388(00)01493-6", volume = "320", year = "2001", } @article{11, author = "I. Zergioti and A. Zervaki and A. Hatziapostolou and Haidemenopoulos, G.N. and E. Hontzopoulos", abstract = "TiC layers have been successfully deposited locally on tool steel specimens and real small industrial tools in order to improve their mechanical and corrosion properties. TiC films have been produced by the pyrolytic laser chemical vapour deposition technique, using a low power RF-modulated CO2 laser and a gas mixture of TiCl4/CCl4/H2/H/Ar. The surface temperature was monitored by a microcomputer-based feedback loop system that was specially developed and integrated to control the laser. SEM, EDX, XRD and TEM analysis showed that close stoichiometric TiC (fcc structure, lattice constant a=4.2{\AA}) was deposited in the films with nanocrystalline structure. The microhardness of the coatings was in the range 2500–3200HK. Furthermore, an ArF excimer laser was used to enhance the deposition rate.", doi = "10.1007/BF00326489", journal = "Journal of Optical and Quantum Electronics", number = "12", pages = "1377-1383", title = "{D}eposition of {R}efractory compounds with {LCVD}", url = "http://www.springerlink.com/content/h041181270501196/", volume = "27", year = "1995", } @article{27, author = "I. Zergioti and M. Velegrakis and Haidemenopoulos, G.N.", abstract = "The composition and the kinetics of the plume produced during the pulsed laser deposition of TiC and TiB2 coatings on metal substrates was studied under film growth conditions. Mass analysis of ions of the ejected material was performed by time of flight mass spectroscopy (TOF-MS) and showed the presence of Ti+, C+ during TiC ablation and B+, B2+, Ti+ during TiB2 ablation. The kinetic energies (KE) of the ions depended on the laser fluence. At the ablation threshold laser fluence (0.5 J/cm2) the KE of the species was less than 1 eV, while, at intermediate fluence regimes (above 1 J/cm2), a significant enhancement of the ablated ions KE (~200 eV) was observed. At higher fluence regimes (above 3 J/cm2), the velocity of the light-emitting particles produced by the excimer laser ablation was measured using a streak camera, between 1.5 and 6×106 cm/s and scaled linearly with laser fluence. These results were used in establishing relations between the nature of the plume produced by target ablation and structural properties of the deposited ceramic films.", journal = "Applied Surface Science", number = "1-2", pages = "92-98", title = "{D}iagnostics of the {I}ons {P}roduced by {L}aser {A}blation of {T}i{C} and {T}i{B}2", url = "http://dx.doi.org/10.1016/S0169-4332(97)00514-X", volume = "126", year = "1998", } @article{24, author = "Sp. G. Pantelakis and Haidemenopoulos, G.N.", abstract = "Conventional paint removal processes, based on application of chemicals and abrasion, are becoming inadequate for modern aircraft structures. In addition they are associated with severe environmental problems, mainly due to the production of hazardous waste. Several alternative novel techniques are being developed. However, the aspect of material property degradation due to the application of these new paint removal techniques has not been addressed adequately. The application of laser radiation (carbon dioxide and excimer), as well as plasma etching, has recently been associated with significant ductility deterioration and fatigue life extension. Residual stress measurements, roughness measurements and fractographic analysis were employed in order to rationalize the effect of these novel paint removal processes on the fatigue behavior of aluminum alloy 2024. The observed enhancement of fatigue life is attributed to the development of compressive residual stresses during paint removal processing. At low fatigue stresses, the magnitude of the residual stress correlates with the relative enhancement in fatigue life for the three processes investigated. The effect of surface roughening towards decreasing fatigue life is surpassed by the effect of residual stresses in extending fatigue life. Finally, the decrease of toughness and associated damage tolerance ability which follows the application of paint removal processes has been confirmed by fractographic measurements.", journal = "Surface and Coatings Technology", keywords = " Laser paint stripping; Plasma etching; Residual stress; Fractographic analysis", number = "2-3", pages = "198-204", title = "{E}ffect of {N}ovel {P}aint {R}emoval {P}rocesses on the {F}atigue {B}ehavior of {A}luminum {A}lloy 2024", url = "http://dx.doi.org/10.1016/S0257-8972(98)00526-X", volume = "106", year = "1998", } @article{62, author = " Kamoutsi, Helen and Haidemenopoulos, G.N. and Bontozoglou, V. and Petroyiannis, P.V. and Pantelakis, S.", journal = "Corrosion Science", pages = "139-142", title = "{E}ffect of {P}rior {D}eformation and {H}eat {T}reatment on the {C}orrosion-{I}nduced {H}ydrogen {E}mbrittlement in {A}luminum {A}lloy 2024", volume = "80", year = "2014", } @article{82, author = "Peter I. Christodoulou and Alexis T. Kermanidis and Gregory N. Haidemenopoulos and Daniel Krizan and Kyriaki Polychronopoulou", abstract = "Abstract The retained austenite (RA) characteristics of Al-containing TRIP700 steels have been manipulated using varying bainitic isothermal transformation (BIT) processing. The microstructural evolution was investigated using optical microscopy and quantitative image analysis, while the amount of transformed RA was evaluated with the saturation magnetization (SM) technique. Cyclic behavior is found to depend on the applied strain amplitude and stability of RA. At strain amplitudes with comparable elastic and plastic strain components, cyclic softening prevails, facilitated by more stable RA microstructures and Low Cycle Fatigue (LCF) performance benefits from a lower RA stability, which controls the amount of cyclic softening rate. With increasing plastic strain component, a transition to cyclic hardening is observed, and the transition strain increases with increasing RA stability. LCF performance deteriorates because of excessive cyclic strain hardening promoting martensitic transformation. The effect is accompanied by a transition from mixed dimple/cleavage to cleavage-type fracture characteristics.", doi = "10.1111/ffe.12972", journal = "Fatigue {\&} Fracture of Engineering Materials {\&} Structures", keywords = "bainitic isothermal transformation, cyclic behavior, formability, retained austenite stability, retained austenite transformation, transformation-induced plasticity steel", number = "5", pages = "1085-1099", title = "{E}ffect of retained austenite stability on cyclic deformation behavior of low-alloy transformation-induced plasticity steels", url = "https://onlinelibrary.wiley.com/doi/abs/10.1111/ffe.12972", volume = "42", year = "2019", } @article{53, author = "A.T. Kermanidis and Zervaki, Anna and Haidemenopoulos, G.N. and Sp.G. Pantelakis", abstract = "The effects of temper condition and corrosion on the fatigue behavior of a laser beam welded Al–Cu–Mg–Ag alloy (2139) have been investigated. Natural aging (T3 temper) and artificial aging (T8 temper) have been applied prior to welding. Corrosion testing has been performed by exposing the welded specimens to a salt spray medium for 720 h. Aging influences the corrosion behavior of laser welds. In the T3 temper, corrosion attack is in the form of pitting in the weld area, while in the T8 temper corrosion is in the form of pitting and intergranular corrosion in the base metal. In the latter case corrosion is attributed to the presence of grain boundary precipitates. Corrosion degrades the fatigue behavior of 2139 welds. The degradation is equal for both the T3 and T8 tempers and for the corrosion exposure selected in this study corresponds to a 52% reduction in fatigue limit. In both cases fatigue crack initiation is associated with corrosion pits, which act as stress raisers. In the T3 temper, the fatigue crack initiation site is at the weld metal/heat affected zone interface, while for the T8 temper the initiation site is at the base metal. Fatigue crack initiation in uncorroded 2139 welds occurs at the weld toe at the root side, the weld reinforcement playing a principal role as stress concentration site. The fatigue crack propagates through the partially melted zone and the weld metal in all cases. The findings in this paper present useful information for the selection of appropriate heat treatment conditions, to facilitate control of the corrosion behavior in aluminium welds, which is of great significance for their fatigue performance.", doi = "10.1016/j.matdes.2009.07.020", journal = "Materials and Design", month = "January", number = "1", pages = "42-49", title = "{E}ffects of {T}emper {C}ondition and {C}orrosion on the {F}atigue {P}erformance of a {L}aser-{W}elded {A}l-{C}u-{M}g-{A}g alloy (2139)", url = "http://dx.doi.org/10.1016/j.matdes.2009.07.020", volume = "31", year = "2010", } @article{63, author = "Spyrou, L.A. and Sarafoglou, P.I. and Aravas, N. and Haidemenopoulos, G.N.", abstract = " ", journal = "Engineering Failure Analysis", pages = "456-469", title = "{E}valuation of {C}reep {D}amage of {INCOLOY} 800{HT} {P}igtails in a {R}efinery {S}team {R}eformer {U}nit", volume = "45", year = "2014", } @article{41, author = "P. V. Petroyiannis and Kamoutsi, Helen and Al. Th. Kermanidis and S. G. Pantelakis and V. Bontozoglou and Haidemenopoulos, G.N.", abstract = "The present work aims to provide evidence of corrosion-induced hydrogen embrittlement of the aircraft aluminium alloy 2024. An extensive experimental investigation involving metallographic and fractographic analyses as well as mechanical testing was performed. The corrosion exposure led to a moderate reduction in yield and ultimate tensile stress and a dramatic reduction in tensile ductility. Metallographic investigation of the specimens revealed a hydrogen-rich embrittled zone just below the corrosion layer. Furthermore, fractographic analyses showed an intergranular fracture at the specimen surface followed by a zone of quasi-cleavage fracture and further below an entirely ductile fracture. Mechanical removal of the corroded layers restored the yield and ultimate stress almost to their initial values but not the tensile ductility. The tensile ductility was restored to the level of the uncorroded material only after heat treatment at 495°C. Measurement of hydrogen evolution with temperature showed that by heating the corroded alloy at 495°C, the trapped hydrogen is released.", journal = "Fatigue and Fracture of Engineering Materials and Structures", keywords = "2024 aluminium alloy;corrosion-induced hydrogen embrittlement;fractographic analysis;metallographic investigation;precorrosion exposure;tensile tests", month = "June", number = "6", pages = "565-574", title = "{E}vidence on the {C}orrosion-induced {H}ydrogen {E}mbrittlement of 2024 {A}l-alloy", url = "http://onlinelibrary.wiley.com/doi/10.1111/j.1460-2695.2005.00900.x/abstract", volume = "28", year = "2005", } @article{5, author = "E. Hontzopoulos and D. Tsipas and Haidemenopoulos, G.N.", journal = "Laser Magazin of Optronics Applications and Innovation", pages = "35-38", title = "{E}xcimer {L}aser {A}ssisted {A}lloying of {H}f{I}4 {L}ayers", volume = "2", year = "1990", } @article{8, author = "J. Mcintosh and A. Zervaki and K. Papadimitriou and G. N. Haidemenopoulos and A. Manousaki and G. Zergioti and E. Hontzopoulos", doi = "10.1155/1993/72409", journal = "Laser Chemistry", pages = "121-128", title = "{E}xcimer {L}aser {U}sed as a {M}aterials {C}haracterization {T}ool: {S}ulphide {I}nclusion {P}rinting in {S}teel", url = "http://dx.doi.org/10.1155/1993/72409", volume = "13", year = "1993", } @article{29, author = "Apostolos N. Vasilakos and Kostas Papamantellos, and Haidemenopoulos, G.N. and Wolfgang Bleck", abstract = "The stability of retained austenil. Is the most ImportwIrrt ~ram.ter controlling tne tre".fOlmaliOfI pI~tlelty offoeu In mulb'~II" low alloy TRIP 1t.,I,. In this wone !he merTnOdynamtc stability 01 me retllr.ad austenite hIlS been determined e_penm!ntally try mElcu.uring the Mf t.mperatv,e ~ I lurtCtlon of bainite i$OlhtlM'nal transformation (elT) t.mpal1lture and 1ime In two low alloy TRIP steels. A single,,~ imtn l,mperalure-vlJri.!l.ble tensIon lest tschniqlJe [SS-TV-TT) nas bHn ImploY$d. whict'l .lIowtcl to link tha appearance 01 yield poh"ltlln tha straM-strain curve with the mechanically-Induced martlll1Slllc transformation of the retOlined austaoi1e. The results Indicattd Ih',lne M.7 Ilimpenrture varies with BIT tempenrture .nd tiN. Highe, austllnlte !I~blilty i!l M!I(leiMeCI with 8 BIT tempe~tur8 of 4OQ'C rather than 37S"C. In addition. the chemical st8blliutlon 01 the retalnQlj austllnlte I'IslSociated with carbon er'lrlchment from the growing btllnlte 15 lowered al snol1 81T tirT'lftS. This $f8billty drop Is dua to cerblde precipijtstion and (lomes earHer In the NkQn\~nlng stlieL At longer elT tlrntS the retained aust8flite dispersion becomes finer am! it:!I !liability rl"!1 due to size swblilution. Tha expe~m.nta\ relulls are In good agreement with model ptet:lieUons within the range of 8f1~clpeted ~rbon enrichment ollhe retained austenite:end maasurttd austenite particle size.", journal = "Steel Research", number = "11", pages = "466-471", title = "{E}xperimental determination of the {S}tability of {R}etained {A}ustenite in {L}ow-{A}lloy {TRIP} {S}teels", volume = "70", year = "1999", } @article{17, author = "Haidemenopoulos, G.N.", journal = "Z.Metallkunde", pages = "529-538", title = "{E}xperimental {I}nvestigation and {T}hermodynamic {C}alculation of the {T}ernary {M}n-{Y}-{Z}r system", volume = "88", year = "1997", } @inbook{2009, author = "Haidemenopoulos, G.N. and P.I. Sarafoglou", title = "{E}xtrudable {A}l-{S}i-{M}g {A}lloys: {S}imulation of {M}icrosegregation and {H}omogenization, {E}ncyclopedia of {A}luminium and {I}ts {A}lloys, {G}eorge {T}otten and {O}llaf {K}essler (editors), {T}aylor and {F}rancis, {ISBN} 9781466510807, {N}ew {Y}ork, {USA}", year = "2018", } @article{73, author = "Christodoulou, P.I. and Kermanidis, A.T. and Haidemenopoulos, G.N.", journal = "Theoretical and Applied Fracture Mechanics, in press accepted manuscript", title = "{F}atigue and fracture behavior of pearlitic {G}rade 900{A} steel used in railway applications", year = "2016", } @inbook{2006, author = "S. Pantelakis and A. Kermanidis and G.A. Papadimitriou and Haidemenopoulos, G.N. and A. Zervaki", title = "{F}atigue performance of 2139 aluminum alloy laser beam welds following exposure to salt spray environment, in {P}article and {C}ontinuum {A}spects of {M}esomechanics (eds {G}. {C}. ", year = "2010", } @article{90, author = "T. Kermanidis and A.D. Zervaki and V.Modas and A.N. Chamos and Sp.G. Pantelakis", abstract = "The role of existing corrosion damage on the fatigue performance of 6156 AA laser beam welds in T3 state, with additional post weld heat treatment T8, has been assessed. The welds were subjected to salt fog environment for 720hours and then metallographically examined to characterize corrosion behaviour. The corrosion results demonstrate that T3/T8 treatment provides high corrosion susceptibility in the weld area, where localized damage in the form of large pits prevails. Fatigue performance of corroded samples is drastically degraded by the presence of corrosion pits which act as stress raisers and accelerate crack initiation in the corroded samples. Fatigue cracks initiate at the root of corrosion pits on the large specimen surfaces in the weld metal area and propagate in through thickness direction. The obtained results have been compared to results from 6156 welds with T4 treatment in as welded conditions.", doi = "https://doi.org/10.1016/j.proeng.2014.06.217", issn = "1877-7058", journal = "Procedia Engineering", keywords = "Fatigue, Corrosion damage, Weld, Post weld heat treatment, Clad aluminium alloy, Stress concentration", note = "XVII International Colloquium on Mechanical Fatigue of Metals (ICMFM17)", pages = "22 - 26", title = "{F}atigue {P}erformance of {P}re-corroded 6xxx {A}luminum {A}lloy {L}aser {B}eam {W}elds with {D}issimilar {H}eat {T}reatment", url = "http://www.sciencedirect.com/science/article/pii/S1877705814007875", volume = "74", year = "2014", } @article{38, author = "Ioannis Papatriantafillou and Nikolaos Aravas and Haidemenopoulos, G.N.", abstract = "A constitutive model that describes the mechanical behaviour of steels exhibiting “Transformation Induced Plasticity” (TRIP) during martensitic transformation is presented. Multiphase TRIP steels are considered as composite materials with a ferritic matrix containing bainite and retained austenite, which gradually transforms into martensite. The effective properties and overall behaviour of TRIP steels are determined by using homogenization techniques for non-linear composites. The eveloped constitutive model considers the different hardening behaviour of the individual phases and estimates the apportionment of plastic strain and stress between the individual phases of the composite. A methodology for the numerical integration of the resulting elastoplastic constitutive equations in the context of the finite element method is developed and the constitutive model is implemented in a general-purpose finite element program. The prediction of the model in uniaxial tension agrees well with the experimental data. The problem of necking of a bar in uniaxial tension is studied in detail.", journal = "Steel Research International", pages = "732-738", title = "{F}inite {E}lement {M}odeling of {TRIP} {S}teels", volume = "75", year = "2004", } @article{81, author = "Maria-Ioanna T. Tzini and Despina A. Karamichailidou and Gregory N. Haidemenopoulos", abstract = "The design of multipass hot-rolling schedules is of great importance to steel industry and an effort is made to predict the microstructure evolution. In the present study, a multi-phase field model is employed for the simulation of the grain size evolution due to static recrystallization and grain growth during multipass hot-rolling of C-Mn steels. A variable stored energy per rolling pass, a temperature dependent interface mobility, and nucleation site density are considered. The model is compared with an extended JMAK model and validated with experimental data obtained from two hot-rolling schedules. The results indicate that both models describe the experimental data well, however the phase field model avoids certain discontinuities between static recrystallization and grain growth. A statistical analysis is conducted to investigate the effect of the microstructure domain size on the phase field results and grain size distributions. The effect of key process parameters on the kinetics of static recrystallization and grain growth are determined by the temporal evolution of equivalent circular grain diameter distributions. Both approaches have the potential to be used for the computational design of multipass hot-rolling processes in steels.", doi = "10.1002/srin.201800223", journal = "steel research international", keywords = "extended JMAK model, grain growth, multipass hot-rolling, multi-phase field model, static recrystallization", number = "11", pages = "1800223", title = "{G}rain {S}ize {E}volution during {M}ultipass {H}ot-{R}olling of {C}-{M}n {S}teels: {C}omparison of {P}hase {F}ield and {E}xtended {JMAK} {M}odeling", url = "https://onlinelibrary.wiley.com/doi/abs/10.1002/srin.201800223", volume = "89", year = "2018", } @article{18, author = "I. Zergioti and C. Fotakis and Haidemenopoulos, G.N.", abstract = "Refractory coatings of TiC and TiB2 have been grown by pulsed laser deposition on Si(100) and on X155 steel at various substrate temperatures ranging from 40°C–650°C. A pulsed KrF excimer laser was used with the deposition chamber at a base pressure of 10−6 mbar. The morphology and structure of the films, studied with scanning electron microscopy (SEM), X-ray diffractometry (XRD) and transmission electron microscopy (TEM) analysis, showed that polycrystalline films with fine morphology of TiC and TiB2 were deposited with grain sizes of 10 nm–70 nm at all substrate temperatures. Shifts in the X-ray diffraction peaks were attributed to the presence of residual stresses in the films, which decreased as the substrate temperature was increased. Finally, the metallic behavior of the coatings was studied by electrical resistivity measurements.", journal = "Thin Solid Films", keywords = "Pulsed laser deposition; Structural properties", number = "1-2", pages = "39-46", title = "{G}rowth of {T}i{B}2 and {T}i{C} {C}oatings using {P}ulsed {L}aser {D}eposition", url = "http://dx.doi.org/10.1016/S0040-6090(97)00128-4", volume = "303", year = "1997", } @article{77, author = "Haidemenopoulos, G.N. and K.N. Malizos and A.D. Zevaki and K. Bargiotas", abstract = "Porous Tantalum is increasingly used as a structural scaffold in orthopaedic applications. Information on the mechanisms of human bone ingrowth into trabecular metal implants is rather limited. In this work we have studied, qualitatively, human bone ingrowth into a retrieved porous tantalum monoblock acetabular cup using optical microscopy, scanning electron microscopy and energy dispersive X-ray analysis. According to the results and taking into account the short operational life (4 years) of the implant, bone ingrowth on the acetabular cup took place in the first two-rows of porous tantalum cells to an estimated depth of 1.5 to 2 mm. The bone material, grown inside the first raw of cells, had almost identical composition with the attached bone on the cup surface, as verified by the same Ca:P ratio. Bone ingrowth has been a gradual process starting with Ca deposition on the tantalum struts, followed by bone formation into the tantalum cells, with gradual densification of the bone tissue into hydroxyapatite. A critical step in this process has been the attachment of bone material to the tantalum struts following the topology of the porous tantalum scaffold. These results provide insight to the human bone ingrowth process into porous tantalum implants.", doi = "10.3934/matersci.2017.6.1220", issn = "2372-0484", journal = "AIMS Materials Science ", keywords = " porous tantalum; bone ingrowth; acetabular cup; osteointegration; tantalum scaffold", number = "6", pages = "1220-1230", title = "{H}uman bone ingrowth into a porous tantalum acetabular cup", url = "https://www.aimspress.com/article/10.3934/matersci.2017.6.1220", volume = "4", year = "2017", } @article{26, author = "Haidemenopoulos, G.N. and N. Hassiotis and G. Papapolymerou and V. Bontozoglou", abstract = "Exfoliation and alternate immersion corrosion were investigated in Al alloy 2024-T3 (UNS A92024) uptake during exposure and to correlate it with corrosion characterization. Characterization involved determination of weight loss, pitting density, and maximum depth of attack. Hydrogen uptake was determined by subsequent hydrogen evolution during heating. In both accelerated corrosion tests, pitting developed into intergranular corrosion and intergranular attack. Hydrogen penetrated through Al 2024-T3. In the exfoliation test, hydrogen concentration correlated well with the increase in available surface area during intergranular attack. There was indirect evidence that the first portions of hydrogen absorbed were arrested chemically inside the specimen. Free hydrogen (which evolves with mild heating) started to build up only after all active sites were occupied.", doi = "10.5006/1.3284830", journal = "Corrosion", keywords = "aerospace applications, Al 2024, aluminum, exfoliation corrosion, hydrogen permeation, immersion testing, intergranular corrosion, intergranular attack, pitting, weight loss", number = "1", pages = "73-78", title = "{H}ydrogen {A}bsorption into {A}luminum {A}lloy 2024-{T}3 {D}uring {E}xfoliation and {A}lternate {I}mmersion {T}esting", url = "http://corrosion.aip.org/resource/1/corrak/v54/i1/p73_s1?isAuthorized=no", volume = "54", year = "1998", } @article{74, author = "Cai, Z. and Ding, H. and Kamoutsi, H. and Haidemenopoulos, G.N.", journal = "Materials Science and Enginnering A", number = "654", pages = "359-367", title = "{I}nterplay between deformation behavior and mechanical properties of intercritically annealed and tempered medium-manganese transformation-induced plasticity steel", year = "2016", } @book{1001, author = "Haidemenopoulos, G.N.", publisher = "Tziolas Publishing", title = "{I}ntroduction to {W}elding, in {G}reek", url = "https://service.eudoxus.gr/search/#a/id:34252/0", year = "2010", } @article{60, author = " Zervaki, Anna and Haidemenopoulos, G.N. and Lambrakos, S.G.", abstract = "Case study analyses of A12139 and Al2198 laser welds are presented. These analyses demonstrate the concept of constructing parameter spaces for prediction of properties within the heat-affected zone (HAZ) of welds using inverse modeling, which are in turn for process control. The construction of these parameter spaces consists of two procedures. One procedure entails calculation of a parameterized set of temperature histories by inverse analysis of the heat deposition occurring during welding. The other procedure entails correlating these temperature histories with a specific physical property of the weld that is measurable. The analyses presented here examines some characteristics of inverse modeling with respect to the prediction of hardness within the HAZ for deep penetration laser welding of the Aluminum alloys A12139 and Al2198. This study further demonstrates the feasibility of constructing a parameter space for the prediction of weld properties using weld cross section measurements that are independent of weld process conditions.", doi = "10.1007/s11665-012-0455-1", issn = "1544-1024", journal = "Journal of Materials Engineering and Performance", keywords = "joining modeling processes welding", number = "6", pages = "1582-1592", title = "{I}nverse {T}hermal {A}nalysis of {H}eat {A}ffected {Z}one in {A}l2129 and {A}l2198 {L}aser {W}elds", url = "http://link.springer.com/article/10.1007%2Fs11665-012-0455-1", volume = "22", year = "2013", } @article{54, author = "Haidemenopoulos, G.N. and Zervaki, Anna and P. Terezakis and J. Tzanis and A.E. Giannakopoulos", doi = "10.1111/j.1460-2695.2006.01048.x", journal = "Fatigue and Fracture of Engineering Materials and Structures", pages = "887-900", title = "{I}nvestigation of {R}olling {C}ontact {F}atigue {C}racks in a {G}rade 900{A} {R}ail {S}teel of a {M}etro {T}rack", url = "http://onlinelibrary.wiley.com/doi/10.1111/j.1460-2695.2006.01048.x/abstract", volume = "29", year = "2006", } @article{80, author = "Gregory N. Haidemenopoulos and Helen Kamoutsi and Kyriaki Polychronopoulou and Panagiotis Papageorgiou and Ioannis Altanis and Panagiotis Dimitriadis and Michael Stiakakis", abstract = "Stress-oriented hydrogen-induced cracking (SOHIC) of an amine absorber column made of a Hydrogen Induced Cracking (HIC) resistant steel and operating under wet H2S service was investigated. SOHIC was not related to welds in the column and evolved in two steps: initiation of HIC cracks in the rolling plane and through-thickness linking of the HIC cracks. Both the original HIC cracks as well as the linking cracks propagated with a cleavage mechanism. The key factors identified were periods with high hydrogen charging conditions, manifested by high H2S/amine ratio, and stress triaxiality, imposed by the relatively large thickness of the plate. In addition, the mechanical properties of the steel away from cracked regions were unaffected, indicating the localized nature of SOHIC.", doi = "10.3390/met8090663", issn = "2075-4701", journal = "Metals", number = "9", title = "{I}nvestigation of {S}tress-{O}riented {H}ydrogen-{I}nduced {C}racking ({SOHIC}) in an {A}mine {A}bsorber {C}olumn of an {O}il {R}efinery", url = "https://www.mdpi.com/2075-4701/8/9/663", volume = "8", year = "2018", } @article{40, author = "P.V. Petroyiannis and Sp.G. Pantelakis and Haidemenopoulos, G.N.", abstract = "The present investigation aims to inquire whether Al cladding of 2024 aluminum alloy specimens could provide, additionally to the expected protection against corrosion damage, also a protection against the corrosion induced hydrogen embrittlement of the alloy. The latter is observed when bare 2024 material is subjected to laboratory exfoliation corrosion exposure also in the absence of mechanical loading. Furthermore, the study aims to ponder on the question whether local Al cladding at small regions of the specimen surface might suffice for protecting the specimen against corrosion damage and hydrogen embrittlement. The work comprises the results of an extensive experimental investigation including tensile tests on precorroded 2024 specimen protected through both complete and local surface Al cladding. Metallographie and fractographic analyses as well as measurements of the hydrogen uptake during the corrosion process.", journal = "Theoretical {\&} Applied Fracture Mechanics", keywords = "Corrosion; Hydrogen embrittlement; Tensile properties degradation; 2024 Al clad; Damage protection; Local surface cladding", number = "1", pages = "70-81", title = "{I}nvestigation on the {P}rotective {R}ole of {L}ocal {A}l {C}ladding against {C}orrosion {D}amage and {H}ydrogen {E}mbritlement of 2024 {A}l alloy {S}pecimens", url = "http://dx.doi.org/10.1016/j.tafmec.2005.05.006", volume = "44", year = "2005", } @article{68, author = " Kamoutsi, Helen and Gioti, E. and Haidemenopoulos, G.N. and Cai, Z. and Ding, H.", journal = "Metallurgical and Materials Transactions A", note = "(accepted, in press).", title = "{K}inetics of solute partitioning during intercritical annealing of a medium-{M}n steel", year = "2015", } @article{64, author = "Haidemenopoulos, G.N. and Aravas, N. and Bellas, I.", journal = "Materials Science and Engineering A", pages = "416-413", title = "{K}inetics of {S}train-{I}nduced {T}ransformation of {D}ispersed {A}ustenite in {L}ow-{A}lloy {TRIP} {S}teels", volume = "615", year = "2014", } @article{70, author = "Haidemenopoulos, G.N. and , ", abstract = "G.N. Haidemenopoulos and A. Katsamas, Laser Carburizing of Steels, Encyclopedia of Iron, Steel and Their Alloys, Rafael Colas and George Totten (editors), Taylor and Francis, New York, USA, 2016 ", address = "New York, USA", editor = "Rafael Colas and George Totten", journal = "Encyclopedia of Iron, Steel and Their Alloys, Rafael Colas and George Totten (editors), Taylor and Francis, New York, USA", publisher = "Taylor and Francis", series = "Encyclopedia of Iron, Steel and Their Alloys", title = "{L}aser {C}arburizing of {S}teels, {E}ncyclopedia of {I}ron, {S}teel and {T}heir {A}lloys", year = "2016", } @article{25, author = ", and Haidemenopoulos, G.N.", abstract = "The response of plain carbon Ck-45 steel to laser trnnsfol111ation hardening is invest igated, and the influence of process conditions such as beam power and size, traverse speed and initial surface condition is examined. Results for Ck-45 and Ck-60 steels arc compared, in an effort to determine the effect of carbon content. Ck-60 steel presented higher case depths than Ck-45, due to the diffcrcnces in the critical austenitization lemperatures between the two steels" Regarding the achieved hardncss, the two steels prcsented smaller differences than those-expccted by their difference in carbon content.", journal = "J. Balk. Trib. Assc", number = "3", pages = "129-140", title = "{L}aser {T}ransformation {H}ardening of {C}k-45 and {C}k-60 {P}lain {C}arbon {S}teels", volume = "4", year = "1998", } @article{21, author = "Haidemenopoulos, G.N.", journal = "J. Balk. Trib. Assc", number = "2", pages = "113-119", title = "{L}aser {T}ransformation {H}ardening of {H}ypoeutectoid {C}k-60 {S}teel", volume = "3", year = "1997", } @inbook{2003, author = "A.D. Zervaki and Haidemenopoulos, G.N.", title = "{L}aser {W}elding of 6xxx {A}luminum {A}lloys, in {M}aterials for {T}ransportation {T}echnology, {V}ol.1 (ed {P}.{J}. {W}inkler) {W}iley-{VCH} {V}erlag {G}mb{H}, {W}einheim, {G}ermany, pp.141-149", year = "2005", } @article{33, author = ", and Haidemenopoulos, G.N.", abstract = "The present study investigated the use of a laser-beam, in order to carburize the surface of DIN 15CrNi6 low-alloy, case-hardening steel. The surface of the material was coated with graphite prior to laser irradiation. Two different kinds of coatings were used: (i) a dilute commercial graphite spray and (ii) a slurry of graphite powder in ethanol. A CO2 laser-beam was used as the heat source, in order to activate the introduction of carbon in the steel surface. Carburizing was achieved by two distinct mechanisms: (a) surface alloying mechanism, which incorporates melting of the substrate and dissolution of the graphite in the liquid phase and (b) solid-state diffusion mechanism, which incorporates austenitization of the substrate and carbon diffusion in austenite. A variety of microstructures and microhardness profiles were produced, depending mainly on the type of graphite coating used, as well as on processing parameters. In general, the carburized layer was accompanied by a heat-affected zone, which was also significantly hardened, mainly due to secondary hardening. Cracking and porosity was observed in some specimens carburized by the surface alloying mechanism, as a result of carbon enrichment and high solidification rates. Finally, an effort was made to investigate the possibility for solid-state diffusion of carbon in austenite, under the short heating times imposed by laser treatment, with the use of computational kinetics simulation.", journal = "Surface and Coatings Technology", number = "2-3", pages = "183-191", title = "{L}aser-{B}eam {C}arburizing of {L}ow-{A}lloy {S}teels", url = "http://dx.doi.org/10.1016/S0257-8972(00)01061-6", volume = "139", year = "2001", } @article{22, author = ", and Zervaki, Anna and Haidemenopoulos, G.N.", abstract = "A carbon dioxide laser with a power of 1.5 kW was employed for surface hardening of a hypoeutectoid Ck-60 steel. The microstructures and hardness profiles were determined as a function of power density and laser beam travel speed. The microstructure in the laser-beam hardened zone depended on power density and consisted of plate martensite (for high power density) or autotempered martensite (for low power density). In the transition zone of the laser-beam treated specimens, martensite and ferrite were observed. Case depth and maximum hardness were found to depend on power density and travel speed. A simple one-dimensional heat flow model has been used for the selection of process parameters and for the prediction of case depth. Calculated and experimentally determined case depths are in good agreement for medium values of power density. ", journal = "Steel Research", number = "3", pages = "119-124", title = "{L}aser-{B}eam {S}urface {T}ransformation {H}ardening of {H}ypoeutectoid {C}k-60 {S}teel", volume = "68", year = "1997", } @article{35, author = "Apostolos N. Vasilakos and Joachim Ohlert and Katerina Giasla and Haidemenopoulos, G.N. and Wolfgang Bleck", abstract = "In recent years the technology of low-alloy TRIP steels has considerably advanced. The mechanical properties are characterised by a combination of high yield strength and high uniform elongation as well as enhanced formability. In the present work an ellort to correlate mochallical properties with the retained austenite stability was made. Two low-alloy TRIP steels were investigated. The first of them represents a typical composition of the low-alloy TRIP steels, while the other one contains aluminum as aUoying etement. The influence of the heat treatment on the mechanical properties and especially on the amount and stability of the retained austenite was determined. The retained austenite stability was measured with a sing!e specimen technique. in which a tensile specimen was used to determine the M~ temperature with a loading-unloading procedure. The results showed that there is a slrong influence of the stability of the retained austenite on the mechanical properties. Increased stability combined with a high amount of retained austenite, exhibited an increase in both, yield strength and uniform elongation while increased amount of retained austenite with low stability did not show the same good combination of mechanical properties. The results clearty indicate that in order to get the maximum TRIP effect. a good combination of austenite stabHily and amount is required.", journal = "Steel Research", number = "6-7", pages = "249-252", title = "{L}ow {A}lloy {TRIP} {S}teels: a correlation between mechanical properties and retained austenite stability", volume = "73", year = "2002", } @inbook{2001, author = "G. Davignon and M. Giovannini and J. Groebner and Haidemenopoulos, G.N. and H. Seifert", editor = "VCH Verlagsgesellschaft, Weinheim - MSI Stuttgart, Germany", isbn = "3-932120-41-8", title = "{M}agnesium-{N}eodymium-{Z}inc {S}ystem, {T}ernary {A}lloys, {V}ol.19", volume = "19", year = "2001", } @inbook{2000, author = "A. Prince and G. Davignon and M. Giovannini and J. Groebner and Haidemenopoulos, G.N. and H. Seifert", isbn = "ISBN 3-932120-41-8", publisher = " VCH Verlagsgesellschaft, Weinheim - MSI Stuttgart, Germany", series = "Ternary Alloys", title = "{M}agnesium-{P}raseodymium-{Z}inc {S}ystem, {T}ernary {A}lloys, {V}ol.18", volume = "18", year = "2001", } @article{13, author = "Sp. G. Pantelakis and Th. B. Kermanidis and Haidemenopoulos, G.N.", abstract = "Paint removal is required in a series of aeronautical procedures such as maintenance and repair. Today's paint stripping processes which are based on application of chemicals and abrasion are inadequate for modern aircraft structures in addition to environmental contamination. several alternative techniques are in progress. However, the aspect of material property degradation when developing novel, alternative paint stripping techniques has not been properly faced up to present. The influence of two novel paint stripping processes on the mechanical properties of the substrate 2024 7351 aluminium alloy has been investigated. The paint stripping processes included laser radiation with excimer, CO2, TEA-C02 and YAG laser sources as well as plasma etching. These processes have been applied for the removal of polyurethane coating which is a typical aeronautical paint system. The results indicated no significant degradation in yield strength and ultimate tensile strength. However a significant degradation in tensile ductility and toughness is observed with the application of all paint stripping processes, the highest degradation being associated with the ultraviolet excimer laser and plasma etching. On the other hand there is a considerable extension in fatigue life, which depends on the paint stripping process and the applied stress amplitude. At high stress there is no appreciable effect while at low stress there is an order of magnitude life extension associated with CO2 laser paint stripping. At moderate stresses, there is an up to sixfold life extension associated with the excimer laser processing.", journal = "J. Theoretical and Applied Fracture Mechanics", number = "2", pages = "139-146", title = "{M}echanical {B}ehavior of {A}l-{A}lloy 2024 subjected to {P}aint {S}tripping by {L}aser {R}adiation and {P}lasma {E}tching", url = "http://dx.doi.org/10.1016/0167-8442(96)00016-X", volume = "25", year = "1996", } @article{79, author = "A.T. Kermanidis and P.I. Christodoulou and E. Hontzopoulos and Haidemenopoulos, G.N. and H. Kamoutsi and A.D. Zervaki", abstract = "The mechanical performance of laser spot welded joints used in Al-Cu and Al-Al thermal absorber systems has been evaluated under different laser welding and mechanical loading conditions. In the experimental investigation, the effect of laser pulse shape and laser heat input on the spot weld strength has been examined under static and cyclic shear loading. The residual strength of spot welds after initial cyclic loading has also been evaluated. The experimental results are supported by metallographic analysis of welds and fractography of failed spot welds. It is concluded that the static and cyclic shear strength is primarily influenced by the laser heat input, which regulates the size of the generated laser spot weld section and to a lesser extent by the laser pulse shape. The influence of laser heat input parameter on the mechanical performance seems not to be as severe in the case of residual strength. This may be associated with the presence of brittle intermetallic compounds in the bimetallic Al-Cu welds which induce small scale defects during the welding process, thus further affecting mechanical performance leading to a reduction of the load bearing capacity of the spot weld.", doi = "https://doi.org/10.1016/j.matdes.2018.05.052", issn = "0264-1275", journal = "Materials {\&} Design", keywords = "Thermal absorber, Laser spot weld, Laser pulse shape, Laser heat input, Cyclic shear test, Shear strength", pages = "148 - 160", title = "{M}echanical performance of laser spot-welded joints in {A}l-{A}l/{C}u solar thermal absorbers", url = "http://www.sciencedirect.com/science/article/pii/S0264127518304374", volume = "155", year = "2018", } @article{76, author = "G. Aktas Celik and S. Polat and S.H. Atapek and Haidemenopoulos, G.N.", abstract = "Among the family of stainless steels, cast austenitic stainless steels (CASSs) are preferably used due to their high mechanical properties and corrosion resistance. These steels owe their properties to their microstructural features consisting of an austenitic matrix and skeletal or lathy type δ-ferrite depending on the cooling rate. In this study, the solidification behavior of CASSs (304L and 316L grades) was studied using ThermoCalc software in order to determine the solidification sequence and final microstructure during cooling. Theoretical findings were supported by the microstructural examinations. For the mechanical characterization, not only hardness measurements but also tribological studies were carried out under dry sliding conditions and worn surfaces were examined by microscopy and 3D profilometric analysis. Results were discussed according to the type and amount of microstructural features. (19) (PDF) Microstructural and Mechanical Characterization of Solidified Austenitic Stainless Steels. Available from: https://www.researchgate.net/publication/320229268_Microstructural_and_Mechanical_Characterization_of_Solidified_Austenitic_Stainless_Steels [accessed Nov 17 2019].", doi = "10.1515/afe-2017-0110", journal = "Archives of Foundry Engineering", keywords = "Theory of crystallization, ThermoCalc, Metallography, Microstructure, Tribology ", number = "3", pages = "163-167", title = "{M}icrostructural and mechanical characterization of solidified austenitic stainless steels", url = "https://www.researchgate.net/publication/320229268_Microstructural_and_Mechanical_Characterization_of_Solidified_Austenitic_Stainless_Steels", volume = "17", year = "2017", } @article{83, author = "Panagiota I. Sarafoglou and Alexandros Serafeim and Ioannis A. Fanikos and John S. Aristeidakis and Gregory N. Haidemenopoulos", abstract = "Control of the homogenization process is important in obtaining high extrudability and desirable properties in 6xxx aluminum alloys. Three consecutive steps of the process chain were modeled. Microsegregation arising from solidification was described with the Scheil-Gulliver model. Dissolution of Mg(2)Si, Si (diamond) and {\^I}texttwosuperior-AlFeSi ({\^I}texttwosuperior-Al(5)FeSi) to {\^I}textpm-AlFeSi ({\^I}textpm-Al(12)(FeMn)(3)Si) transformation during homogenization have been described with a CALPHAD-based multicomponent diffusion Dual-Grain Model (DGM), accounting for grain size inhomogeneity. Mg(2)Si precipitation and associated strengthening during homogenization cooling were modeled with the Kampmann-Wagner Numerical (KWN) precipitation framework. The DGM model indicated that the fractions of {\^I}texttwosuperior-AlFeSi and {\^I}textpm-AlFeSi exhibit an exact spatial and temporal correspondence during transformation. The predictions are in good agreement with experimental data. The KWN model indicated the development of a bimodal particle size distribution during homogenization cooling, arising from corresponding nucleation events. The associated strengthening, arising from solid solution and precipitation strengthening, was in good agreement with experimental results. The proposed modeling approach is a valuable tool for the prediction of microstructure evolution during the homogenization of 6xxx aluminum alloys, including the often-neglected part of homogenization cooling.", day = "01", doi = "10.3390/ma12091421", issn = "1996-1944", journal = "Materials (Basel, Switzerland)", keywords = "aluminum alloys", month = "May", note = "31052397[pmid]", number = "9", pages = "1421", publisher = "MDPI", title = "{M}odeling of {M}icrosegregation and {H}omogenization of 6xxx {A}l-{A}lloys {I}ncluding {P}recipitation and {S}trengthening {D}uring {H}omogenization {C}ooling", url = "https://www.ncbi.nlm.nih.gov/pubmed/31052397", volume = "12", year = "2019", } @article{14, author = "Haidemenopoulos, G.N. and , ", journal = "Steel Research", number = "11", pages = "513-519", title = "{M}odelling of {A}ustenite {S}tability in {L}ow-{A}lloy {T}riple-{P}hase {S}teels", volume = "67", year = "1996", } @article{47, author = " Pappa, Eleanna and Haidemenopoulos, G.N.", abstract = "A simulation of the evolution of the as-cast microstructure during the homogenization heat treatment of A6061 aluminum alloy is presented. The microstructure is dendritic with phase and solute segregation. The alloy microsegregation, which results after casting, was calculated with the Scheil equation by employing computational alloy thermodynamics. The microstructure evolution during homogenization was simulated by employing computational kinetics for the solution of the multicomponent diffusion equations. The composition profiles of the alloying elements and the volume fraction of the secondary phases were calculated as a function of homogenization time. The simulation results were validated qualitatively by comparison with metallographic examinations. During homogenization, the Mg2Si dissolution and the transformations of the Fe-intermetallics were confirmed. It is concluded that the model reproduces the homogenization kinetics reasonably and it is capable for the prediction of the homogenization heat treatment completion times. ", journal = "Journal of Materials Processing Technology", keywords = "Continuous casting; Intermetallics; Microsegregation; Homogenization; Simulation", pages = "63-73", title = "{M}odelling of {S}egregation and {H}omogenization of 6061 {E}xtrudable {A}l-{A}lloy", url = "http://dx.doi.org/10.1016/j.jmatprotec.2007.03.126", volume = "194", year = "2007", } @article{37, author = ", and Haidemenopoulos, G.N. and Nikolaos Aravas", abstract = "Industrial processing at low-alloy Transformalion Induced Plasticity (TRIP) steels involves various stages of heat-treating, such as Intercritical Annealing (IA) and Bainitic Isothermal Treatment (Bin, in order to produce a dispersion of retained austenite (YR) particles and bainite (825OC). II was also observed that kinetic and tllermodynamic predictions set a lower and an upper limit, respectively, within which the actual amount of austenite experimentally observed is contained. Results from the simulation of the BIT indicated considerable carbon enrichment, and thus stabilization of YR, in agreement with recent experimental observations. As regards the strain-induced YA-U' transformation, the analytical model employed in the present work was fitted to available experimental results, showing reasonably good adaptation to the kinetic behaviour of Ihe microstructure during plastic deformation.", journal = "Steel Research Int", pages = "737-743", title = "{M}odelling of transformation in {TRIP} steels", volume = "75", year = "2004", } @inbook{2005, author = "Haidemenopoulos, G.N. and A. Katsamas and A. Aravas", title = "{M}ultiscaling {E}ffects in {TRIP} {S}teels, in {M}ultiscaling in {M}olecular and {C}ontinuum {M}echanics: {I}nteraction of {T}ime and {S}ize from {M}acro to {N}ano, ed. {G}. {S}ih, {S}pringer", year = "2007", } @article{32, author = "Zergioti, I. and Haidemenopoulos, G.N. and Fotakis, C.", abstract = "Nanocrystalline coatings of TiC and TiB2 were grown by pulsed laser deposition on Si(100) and on X155 steel at low substrate temperatures ranging from 40 °C to 650 °C. A pulsed KrF excimer laser was used with the deposition chamber at a base pressure of 10-6 mbar. The morphology and structure of the films, studied with SEM, XRD, and TEM, showed that nanocrystalline films with a fine morphology of TiC and TiB2 were deposited with a grain size of 10 nm-70 nm at all substrate temperatures. The growth of the polycrystalline coatings possessed a columnar morphology with a preferred orientation. The hardness of the coatings was determined to be 40 GPa and the elastic modulus, 240 GPa. The composition and the kinetics of the plume produced during the pulsed laser deposition of TiC and TiB2 was studied under film growth conditions. The mass analysis of ions of the ejected material was performed by time-of-flight mass spectroscopy (TOF-MS) and showed the presence of Ti+ and C+ during TiC ablation and B+, B2+, and Ti+ during TiB2 ablation. The kinetic energies (KE) of the ions depended on the laser fluence which was between 0.5 eV and 340 eV. The kinetic energy and the evolution of the plasma was studied with a streak camera. The velocity of the plasma was of the order of 106 cm/sec and was linearly dependent on the energy fluence of the laser. The emission spectroscopy of the plasma plume confirmed the atomic neutral and single excited species of Ti. These results show that coating growth basically occurs by the recombination of the ionic species at the surface of the substrate.", journal = "Applied Physics A", pages = "s427-s431", title = "{N}anocrystalline {G}rowth and {D}iagnostics of {T}i{C} and {T}i{B}2 {H}ard {C}oatings by {P}ulsed {L}aser {D}eposition", url = "http://www.springerlink.com/content/9n2h97vjnguf92ad/", volume = "70", year = "2000", } @article{61, author = "Haidemenopoulos, G.N. and Kermanidis, A.T. and Maliaros, C. and Dickert, H.H. and Kucharzyk, P. and Bleck, W.", abstract = ", ", journal = "Materials Science and Engineering A", pages = "7- 11", title = "{O}n the effect of austenite stability on high cycle fatigue of {TRIP} 700 steel", volume = "573", year = "2013", } @article{19, author = "I. Zergioti and Haidemenopoulos, G.N.", abstract = "Thin films of TiC and TiB2 have been deposited on silicon substrate by pulsed laser deposition technique, under substrate temperatures 25–600 °C. Transmission electron microscopy revealed the nanocrystalline structure of the coatings. The grain size for the TiC film was between 10 and 70 nm and for the TiB2 film was between 10 and 50 nm ", journal = "Nanostructured Materials", number = "1", pages = "55-59", title = "{O}n the nanocrystalline structure of {T}i{C} and {T}i{B}2 produced by laser ablation", url = "http://dx.doi.org/10.1016/S0965-9773(97)81417-1", volume = "8", year = "1997", } @article{4, author = "Haidemenopoulos, G.N. and M. Grujicic and G. B. Olson and Morris Cohen", abstract = "The most important factors affecting the dispersed-phase transformation toughening in steels are the stability of the dspersed austenhe and the transformation volume change. Both depend on the composition of the steel. The THERMOCALC computer program was used to describe the effect of composition on austenite stability while a formulation based on the two-gamma states model allowed the description of the compositional dependence of the lattice parameters taking into account magneto-volume effects in the austenite.", journal = "CALPHAD", month = "July-August", number = "3", pages = "215-223", title = "{O}n the {O}ptimization of {P}recipitated {A}ustenite for the {T}ransformation {T}oughening of {S}teels", url = "http://dx.doi.org/10.1016/0364-5916(89)90001-1", volume = "13", year = "1989", } @article{20, author = "Haidemenopoulos, G.N. and A. N. Vasilakos", abstract = "The effect of retained austenite on the mechanical behavior of quenched and tempered steels depends on its thermodynamic stability against mechanically-induced martensitic transformation during loading. In this work, the stability of retained austenite is characterized by the Md, temperature and experimentally determined values of the Md, temperature are compared with model predictions. The comparison suggests that significant carbon stabilization of the retained austenite occurs during tempering for both, high and low temperature, austenitizing treatments employed. In addition, it appears that the assumption of a fully-biased rather than a fully-random distribution of nucleation-site potencies is in better agreement with the observed experimental behavior. Finally, the stress state dependence of the retained austenite stability could account for the mechanical behavior variation reported in literature.", journal = "Journal of Alloys and Compounds", keywords = "Retained austenite; Thermodynamic stability; Transformation plasticity", number = "1-2", pages = "128-133", title = "{O}n the {T}hermodynamic {S}tability of {R}etained {A}ustenite in 4340 {S}teel", url = "http://dx.doi.org/10.1016/S0925-8388(96)02574-1", volume = "247", year = "1997", } @article{65, author = "Sarafoglou, P.I. and Haidemenopoulos, G.N.", journal = "Int. Journal of Materials Research", pages = "1202-1208", title = "{P}hase {F}raction {M}apping in the {A}s-{C}ast {M}icrostructure of {E}xtrudable 6xxx {A}luminum {A}lloys", volume = "105", year = "2014", } @article{87, author = "C. G. Prosgolitis and S. G. Lambrakos and A. D. Zervaki", abstract = "This work presents simulation of microstructure evolution in the nugget zone (NZ) of a AZ31-Mg-alloy friction stir weld. The process parameters (tool geometrical characteristics, rotational speed, travel speed, applied load) have been correlated with the resulting microstructural features in the NZ of the weld (grain size and population) with the aid of the MICRESS software, which provides the ability to simulate both nucleation and grain growth during dynamic recrystallization phenomena evolving in the NZ during the weld thermal cycle. The input parameters of the developed model include the tool geometry, the welding conditions as well as the recrystallization energy, the grain boundary mobility and specific material properties. NZ microstructure obtained by simulation shows good agreement with experimental measurements for both grain population and size.", day = "01", doi = "10.1007/s11665-018-3471-y", issn = "1544-1024", journal = "Journal of Materials Engineering and Performance", month = "Oct", number = "10", pages = "5102--5113", title = "{P}hase-{F}ield {M}odeling of {N}ugget {Z}one for a {AZ}31-{M}g-{A}lloy {F}riction {S}tir {W}eld", url = "https://doi.org/10.1007/s11665-018-3471-y", volume = "27", year = "2018", } @book{1000, author = "Haidemenopoulos, G.N.", abstract = "H Φυσική Μεταλλουργία είναι η επιστήμη των μετάλλων και των κραμάτων με κεντρικό πυρήνα την συσχέτιση μεταξύ της κατεργασίας της δομής και των ιδιοτήτων των μεταλλικών υλικών. Το βιβλίο αυτό απευθύνεται σε όσους θέλουν να κατανοήσουν τον τρόπο με τον οποίο διαμορφώνεται η δομή των μετάλλων και τους μηχανισμούς με τους οποίους μετασχηματίζεται η δομή έτσι ώστε τα υλικά να αποκτήσουν τις επιθυμητές ιδιότητες. Η ύλη του βιβλίου αναπτύσσεται σε δέκα κεφάλαια: Εισαγωγή και Ιστορική Αναδρομή - Η Δομή των Μετάλλων - Ατέλειες στην Δομή - Θερμοδυναμική και Διαγράμματα Φάσεων - Διάχυση - Μετασχηματισμοί Φάσεων - Στερεοποίηση - Πλαστική Παραμόρφωση, Ανόπτηση και Ισχυροποίηση - Θραύση, Κόπωση και Ερπυσμός των Μετάλλων - Φυσική Μεταλλουργία των Χαλύβων. Το βιβλίο περιλαμβάνει λυμένα παραδείγματα και ασκήσεις καθώς 7 Case Studies για την εφαρμογή της θεωρίας", publisher = "Tzliolas Publishing", title = "{P}hysical {M}etallurgy", url = "https://service.eudoxus.gr/search/#a/id:9590/0", year = "2007", } @book{1004, author = "Haidemenopoulos, G.N.", isbn = "978-1-138-62768-0", publisher = "CRC Press, Taylor {\&} Francis", title = "{P}hysical {M}etallurgy – {P}rinciples and {D}esign, in {E}ngli", url = "https://www.crcpress.com/Physical-Metallurgy-Principles-and-Design/Haidemenopoulos/p/book/9781138627680", year = "2018", } @article{78, author = "Haidemenopoulos, G.N. and M. Constantinou and H. Kamoutsi and D. Krizan and I. Bellas and L. Koutsokeras and G. Constantinides", abstract = "X-ray diffraction analysis, magnetic force microscopy, and the saturation magnetization method have been employed to study the evolution of the percentage and size of retained austenite (RA) particles during strain-induced transformation in a transformation-induced plasticity (TRIP) steel. A low-alloy TRIP-700 steel with nominal composition Fe-0.2C-0.34Si-1.99Mn-1Al (mass%) was subjected to interrupted tensile testing at strain levels of 0–22% and the microstructure subsequently studied. The results of the three experimental techniques were in very good agreement regarding the estimated austenite volume fraction and its evolution with strain. Furthermore, this multitechnique approach revealed that the average particle size of RA reduced as the applied strain was increased, suggesting that larger particles are less stable and more susceptible to strain-induced phase transformation. Such experimentally determined evolution of the austenite size with strain could serve as an input to kinetic models that aim to predict the strain-induced transformation in low-alloy TRIP steels.", doi = " https://doi.org/10.1007/s11837-018-2832-1", issn = "1543-1851", journal = "Journal of Metals (JOM)", number = "6", pages = "924-928", title = "{P}robing the evolution of retained austenite in {TRIP} steel during strain-induced transformation: a multitechnique investigation", url = "https://link.springer.com/article/10.1007/s11837-018-2832-1", volume = "70", year = "2018", } @article{92, author = "H. Vazarlis and I. Halikia and A. Zervaki", journal = "Mining {\&} Metallurgical Annals", pages = "23-30", title = "{P}roduction of {F}errochrome by using {G}reek {L}ignite {C}oke. {T}he {D}istribution of {S}ulphur", volume = "70", year = "1989", } @article{9, author = "I. Zergioti and A. Hatziapostolou and E. Hontzopoulos and A. Zervaki and Haidemenopoulos, G.N.", abstract = "TiC layers have been successfully deposited locally on D2 tool steel specimens and miniature industrial tools with the aim to improve their mechanical and chemical surface properties. The deposition process was based on a pyrolytically-induced chemical reaction of TiCl4 and CCl4 compounds combined with an atomic hydrogen source. Local heating of the substrate was achieved by means of a 100 W CO2 laser controlled by a microcomputer-based feedback loop system, involving ondashline substrate temperature monitoring. Scanning electron microscopy, energy-dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy analysis showed that close-stoichiometric TiC (fcc structure, lattice constant a =4.2 {\AA}) was deposited in the films with a nanocrystalline structure. The microhardness of the coatings was in the range 2500–3200 HK.", journal = "Thin Solid Films", keywords = "Carbides; Chemical vapour deposition; Deposition process; Titanium carbide", number = "1-2", pages = "96-100", title = "{P}yrolytic {L}aser-{B}ased {C}hemical {V}apor {D}eposition of {T}itanium {C}arbide {C}oatings", url = "http://dx.doi.org/10.1016/0040-6090(95)06906-2", volume = "271", year = "1995", } @article{10, author = "Haidemenopoulos, G.N. and Katerina Papadimitriou", journal = "Steel Research", number = "10", pages = "433-438", title = "{R}etained {A}ustenite and {M}echanical {P}roperties in {B}ainite {T}ransformed {L}ow-alloy {S}teels", volume = "66", year = "1995", } @article{72, author = "Haidemenopoulos, G.N. and Sarafoglou, P. I. and Christopoulos, P. and Zervaki, Anna", journal = "Fatigue and Fracture of Engineering Materials and Structures, in press accepted manuscript", title = "{R}olling contact fatigue cracking in rails subjected to in-service loading", year = "2016", } @book{1003, author = "D.I. Pantelis and V.J. Papazoglou and Haidemenopoulos, G.N.", isbn = "978-960-418-658-7", publisher = "Tziolas Publishing", title = "{S}cience and {T}echnology of {W}elding, in {G}reek", url = "https://www.tziola.gr/book/epistimi-ke-technologia-ton-sygkolliseon/", year = "2011", } @article{67, author = "Sarafoglou, P.I. and Tzini, M.I.T. and Haidemenopoulos, G.N.", journal = "Int. Journal of Materials Research and Metallurgical Engineering", title = "{S}imulation of cyclic transformations in the intercritical range of a 5{M}n steel", year = "2015", } @article{31, author = ", and , ", journal = "Steel Research", number = "9", pages = "351-356", title = "{S}imulation of {I}ntercritical {A}nnealing in {L}ow-alloy {TRIP} {S}teels", volume = "71", year = "2000", } @article{59, author = "Haidemenopoulos, G.N. and Kamoutsi, Helen and Zervaki, Anna", abstract = "A computational simulation of the β-AlFeSi to α-AlFeSi transformation has been performed in this work by integrating the process steps of solidification and homogenization. The composition profiles of alloying elements as well as the profiles of weight fractions of all solid phases computed after solidification were entered as input for the simulation of the homogenization process which involves the dissolution of the Mg2Si and the transformation of β-AlFeSi to α-AlFeSi intermetallics. The transformation fraction was computed as a function of homogenization temperature and time and the transformation kinetics compares well with published experimental data. The evolution of α-AlFeSi weight fraction profile and the effect of grain size on transformation kinetics were also computed.", doi = "http://dx.doi.org/10.1016/j.jmatprotec.2012.06.026", journal = "Journal of Materials Processing Technology", number = "11", pages = "2255-2260", title = "{S}imulation of the transformation of iron intermetallics during homogenization of 6xxx series extrudable aluminum alloys", url = "http://www.sciencedirect.com/science/article/pii/S0924013612002051", volume = "212", year = "2012", } @article{42, author = "Haidemenopoulos, G.N. and , and Nikolaos Aravas", abstract = "Industrial processing of low-alloy Transformation Induced Plasticity (TRIP) steels involves various stages of heat-treating, such as Intercritical Annealing (IA) and Bainitic Isothermal Treatment (BIT), in order to produce a dispersion of retained austenite (gamma(R)) particles and bainite (alpha(B)) in a ferritic matrix (alpha). Retained austenite then transforms to martensite (alpha') during forming processes undergone by the steel. In the present work an effort was made to model these stages of processing, i.e. IA, BIT and the gamma(R)-->alpha' strain-induced transformation. Simulation of heat-treatment stages was implemented using computational kinetics methods. Investigation of the strain-induced alpha(R)-->alpha' transformation kinetics was performed by means of a simple analytical model. Simulation of IA and comparison with available experimental data showed that the amount of austenite (gamma) forming during IA reaches the values predicted by thermodynamic equilibrium only at high annealing temperatures (>825degreesC). It was also observed that kinetic and thermodynamic predictions set a lower and an upper limit, respectively, within which the actual amount of austenite experimentally observed is contained. Results from the simulation of the BIT indicated considerable carbon enrichment, and thus stabilization of gamma(R), in agreement with recent experimental observations. As regards the strain-induced gamma(R)-->alpha' transformation, the analytical model employed in the present work was fitted to available experimental results, showing reasonably good adaptation to the kinetic behaviour of the microstructure during plastic deformation.", issn = "16113683", journal = "Steel Research International", number = "9-10", pages = "720-726", title = "{S}tability and {C}onstitutive {M}odelling in {M}ultiphase {TRIP} {S}teels", volume = "77", year = "2006", } @article{39, author = ", and Haidemenopoulos, G.N. and Zervaki, Anna and I. Melas", abstract = "The present work analyses the failure of a Ni-Cu MONEL 400 alloy tube, which operated as part of a pipeline in a petrochemical distillery installation. The pipeline is used to carry a stream of gaseous hydrocarbons containing hydrochloric acid (HCl) into a reaction tower filled with caustic solution (NaOH), in order to remove HCl from the stream, before the later is directed to a burner. Failure occurred in the form of through-thickness cracking at a bended tube of the pipeline. Metallographic examination revealed intergranular cracking, as well as substantial branching of the observed cracks. Although nominal chemical composition of the component was found to lie within the specified range, EDX microanalysis indicated significant segregation of S and Cl on grain-boundaries. Failure was attributed to stress corrosion cracking (SCC), due to the effect of hypochlorous acid (HClO), formed by the reaction of HCl with atmospheric O2, which entered the tube during shutdowns/startups of the installation. The phenomenon was assisted by residual stresses, originating from the lack of stress-relief annealing after the in-situ bend forming of the tube during assembly of the line, by local reduction of ductility due to bending, as well as by the segregation of S on grain-boundaries.", journal = "Journal of Failure Analysis and Prevention", number = "6", pages = "44-50", title = "{S}tress {C}orrosion {C}racking of a {MONEL} 400 {T}ube", url = "http://www.springerlink.com/content/864w6kg47343uhu3/", volume = "4", year = "2004", } @article{28, author = ", and Haidemenopoulos, G.N.", abstract = "The study investigates laser transformation hardening in the low-alloy 15CrNi6 case-hardening steel. The effect of process parameters such as beam power, beam diameter and travel speed on microstructure, case depth and hardness was examined. In addition, the effect of surface preparation was also investigated. For this purpose, all specimens were initially sandblasted, while some of these were additionally coated with graphite in order to enhance surface absorptivity. In most cases, a heat affected zone (H.A.Z.) had formed below the surface which consisted of two discrete areas, a surface layer and a transition area between this surface layer and the base metal. The microstructure of the surface layer was found to consist of lath martensite, while carburization was found for certain process conditions in the graphite-coated specimens. The transition area consisted of a dispersion of fine carbides in a ferrite matrix. A substantial increase in surface hardness was achieved, by a factor of 2.5 times the base metal hardness. Depths of the H.A.Z. up to approximately 0.6 mm were obtained, without surface melting. The additional use of graphite coating enhanced, in most cases, the coupling of laser-beam to the surface, resulting in greater H.A.Z. depths.", journal = "Surface and Coatings Technology", number = "2-3", pages = "249-255", title = "{S}urface {H}ardening of {L}ow-{A}lloy 15{C}r{N}i6 {S}teel by {CO}2 {L}aser {B}eam", url = "http://dx.doi.org/10.1016/S0257-8972(99)00246-7", volume = "115", year = "1999", } @article{50, author = "A.Chamos and S. Pantelakis and Kamoutsi, Helen and Haidemenopoulos, G.N.", abstract = "The mechanical behaviour of two hot rolled magnesium alloys, namely the AZ31 and AZ61, has been evaluated experimentally under both monotonic and cyclic loading. Both longitudinal (L) and long transverse (LT) directions were evaluated. The tensile behaviour of the L and LT directions is similar and differs only in the offset 0.2% yield strength for both materials. This difference is attributed to the angular spread of basal poles toward the rolling direction and is more pronounced for the case of AZ31. A distinct hardening response is obvious in both directions. Twinning formation was observed; it is more pronounced in the longitudinal direction while the fracture mode is intergranular and equiaxed facets are present in the fracture surfaces of the specimens. The S–N curves exhibit a smooth transition from the low to high cycle fatigue regime. AZ61 exhibits an overall better fatigue behaviour compared to AZ31. A transgranular crack initiation mode is observed in all tested specimens while the propagation of the cracks is characterized as intergranular.", doi = "10.1111/j.1460-2695.2008.01267.x", journal = "Fatigue and Fracture of Engineering Materials and Structures", number = "9", pages = "812-821", title = "{T}ensile and {F}atigue {B}ehavior of {W}rought {M}agnesium {A}lloys {AZ}31 and {AZ}61", url = "http://onlinelibrary.wiley.com/doi/10.1111/j.1460-2695.2008.01267.x/abstract", volume = "31", year = "2008", } @article{51, author = "A. T. Kermanidis and Zervaki, Anna and Haidemenopoulos, G.N. and Sp. G. Pantelakis", abstract = "Laser welding is increasingly used for the fabrication of lightweight and cost-effective integral stiffened panels in modern civil aircraft. As these structures age in service, the issue of the effect of corrosion on their damage tolerance requires attention. In this work, laboratory data on the influence of salt fog corrosion on the fatigue behavior of cladded 6156 T4 aluminum alloy laser welded specimens are presented. The experimental investigation was performed on 6156 T4 laser butt welded sheets. Prior to fatigue testing the welded joints were exposed to laboratory salt fog corrosion exposure for 720 h. The results showed that the clad layer offers sufficient corrosion protection both on base metal and the weld. Fatigue testing was followed by standard metallographic analysis in order to identify fatigue crack initiation sites. Crack initiation is located in all welded samples near the weld reinforcement which induces a significant stress concentration. Localized corrosion attack of the clad layer, in the form of pitting corrosion, creates an additional stress concentration which accelerates crack initiation leading to shorter fatigue life relative to the uncorroded samples. The potency of small corrosion pits to act as stress concentration sites has been assessed analytically. The above results indicate that despite the general corrosion protection offered by the clad layer, the localized attack described above leads to inferior fatigue performance, a fact that should be taken under consideration in the design and maintenance of these structures. ", doi = "10.1007/s10853-010-4429-0", journal = "Journal of Materials Science", number = "16", pages = "4390–4400", title = "{T}he {I}nfluence of {S}alt fog {E}xposure on the {F}atigue {P}erformance of {A}lclad 6xxx {A}luminum {A}lloys {L}aser {B}eam {W}elds", url = "http://www.springerlink.com/content/31277037472k3121/", volume = "45", year = "2010", } @inbook{2004, author = "A.N. Vasilakos and Haidemenopoulos, G.N.", title = "{T}he stability of {R}etained {A}ustenite in {L}ow-{A}lloy {TRIP} {S}teels, in {S}teel and {M}aterials for {P}ower {P}lants, {V}ol.7 (eds. {P}. {N}eumann, {D}. {A}llen, and {E}. {T}eukhoff) {W}iley-{VCH} {V}erlag {G}mb{H}, {W}einheim, {G}ermany, pp.213-218", year = "2006", } @article{88, author = "V. Athanasiou and A.D. Zervaki and E. Papamichos and A. Giannakopoulos", doi = "https://doi.org/10.1016/j.ijrmms.2016.01.006", issn = "1365-1609", journal = "International Journal of Rock Mechanics and Mining Sciences", keywords = "Knoop indentation, Hardness, Cement paste", pages = "241 - 247", title = "{T}he use of {K}noop indentation for the assessment of the elastic properties of mortars and natural stones", url = "http://www.sciencedirect.com/science/article/pii/S1365160916300065", volume = "83", year = "2016", } @article{15, author = ", and Haidemenopoulos, G.N. and P. Polatidis", journal = "METALL 50", pages = "556-560", title = "{T}hermodynamic {A}nalysis and {M}echanical {P}roperties of {C}ast {A}luminium {A}lloy {A}357 with {C}u, {A}g and {S}m {A}dditions", volume = "9", year = "1996", } @article{12, author = "Haidemenopoulos, G.N. and M. Grujicic and G. B. Olson and M. Cohen", abstract = "Transformation toughening has been widely applied in metastable austenitic steels. Recently this toughening mechanism has been extended to ultrahigh strength secondary-hardening martensitic steels, bearing suitable austenitic dispersions. The resulting dispersed-phase transformation toughening depends on the stability of the austenitic dispersions. The stability of dispersed austenite depends on various factors including the chemical composition and size of austenite particles, the stress state and the yield strength of the matrix. A single-parameter characterization of the stability of the austenitic dispersion is provided by the Ms temperature and a functional form relating that temperature with the above-mentioned factors is developed. The microstructural requirements for dispersed-phase transformation toughening are then derived in terms of the austenite particle size and chemical enrichment in stabilizing solutes. Compositional effects on austenite stability have been studied by performing thermodynamic calculations using the Thermo-Calc software. The free-energy change ΔGch = Gb.c.c. − Gf.c.c. for martensitic transformation (a measure of austenite stability) has been evaluated as a function of composition in the ternary Fe---Ni---Co system. This information, when superimposed on isothermal sections at the tempering temperatures of interest, provides a way for selecting alloy compositions that maximize the thermodynamic stability of dispersed austenite.", doi = "0.1016/0925-8388(94)06015-0", journal = "Journal of Alloys and Compounds", pages = "142-147", title = "{T}hermodynamics-{B}ased {A}lloy {D}esign {C}riteria for {A}ustenite {S}tabilization in the {F}e-{N}i-{C}o {S}ystem", url = "http://dx.doi.org/10.1016/0925-8388(94)06015-0", volume = "220", year = "1995", } @article{52, author = "Haidemenopoulos, G.N. and , and Kamoutsi, Helen", abstract = "Alloying additions of Sc and Zr raise the yield strength of Al-Mg alloys significantly. We have studied the effects of Sc and Zr on the grain refinement and recrystallization resistance of Al-Mg alloys with the aid of computational alloy thermodynamics. The grain refinement potential has been assessed by Scheil–Gulliver simulations of solidification paths, while the recrystallization resistance (Zener drag) has been assessed by calculation of the precipitation driving forces of the Al3Sc and Al3Zr intermetallics. Microstructural performance indices have been derived, used to rank several alloy composition variants, and finally select the variant with the best combination of grain refinement and recrystallization resistance. The method can be used, with certain limitations, for a thermodynamics-based design of Al-Mg and other alloy compositions.", doi = "10.1007/s11661-009-0168-8", journal = "Metallurgical and Materials Transactions A", number = "4", pages = "888-899", title = "{T}hermodynamics-{B}ased {C}omputational {D}esign of {A}l-{M}g-{Z}r-{S}c {A}lloys", url = "http://www.springerlink.com/content/k6k7472258284368/", volume = "41", year = "2010", } @article{3, author = "Haidemenopoulos, G.N. and M Grujicic and G.B Olson and Morris Cohen", abstract = "The reversal in the temperature dependence of the elastic limit accurately determines the Ms temperature of retained austenite in 4340 steel. Two models, one based on an exponential distribution of pre-existing nucleation sites and another based on an autocatalytic-site potency distribution, were compared in predicting the constitutive behavior of the steel in the stress-assisted transformation regime (Tation regime. ", doi = "10.1016/0001-6160(89)90134-X", journal = "Acta Metallurgica", month = "June", number = "6", pages = "1677-1682", title = "{T}ransformation {M}icroyielding of {R}etained {A}ustenite", url = "http://dx.doi.org/10.1016/0001-6160(89)90134-X", volume = "37", year = "1989", } @article{2, author = "Haidemenopoulos, G.N. and G.B. Olson and Morris Cohen and K. Tsuzaki", doi = "10.1016/0036-9748(89)90412-2", journal = "Scripta Metallurgica", month = "February", number = "2", pages = "207-212", title = "{T}ransformation {P}lasticity of {R}etained {A}ustenite in {S}tage-{I} {T}empered {M}artensitic {S}teels", url = "http://dx.doi.org/10.1016/0036-9748(89)90412-2", volume = "23", year = "1989", } @article{36, author = "Haidemenopoulos, G.N.", journal = "Steel Research Int", number = "11", pages = "701-702", title = "{TRIP}-{S}teels-{C}orrelation between {M}icrostructure and {P}roperties", volume = "75", year = "2004", } @article{84, author = "A. Chotzoglou and M. Pissas and A. D. Zervaki and G. N. Haidemenopoulos and T. Pissas", abstract = "The rolling contact fatigue cracks (RCF), produced at the surface of the rail tracks, can be detected using a magnetooptical (MO) sensor. Rail tracks are carbon steels with pearlite microstructure. This microstructure has a lamellar texture composed of alternating layers of ferrite and cementite. Both phases are soft ferromagnetic materials at room temperature. If an external magnetic field is applied on the surface of a rail track, the reduced magnetic permeability causes a magnetic leakage field above the cracks. When the external magnetic field is removed, in most cases, a residual stray magnetic field remains above the cracks. When a MO sensor is placed on the surface of the rail track, the sudden change of the stray remanent magnetic field near a crack, yields a significant rotation of the polarization plane of the reflected light, resulting in high MO contrast, exactly above the cracks. Using a polished surface and a cross-section from the head of the rail track, we succeeded in visualizing the RCF cracks in the laboratory. The RCF cracks can also be detected on the surface of the rail track, in field measurements, using a portable commercial polarized light microscope equipped with a MO sensor. Finally, we use computer vision methods, to automatically detect the RCF cracks, using video recorded by displacing the portable microscopy with the MO sensor, on the surface of the rail tracks. We tested an unsupervised automatic crack detection algorithm, which exploits the tubular contrast of the RCF cracks to pinpoint the pixels that correspond to them.", day = "16", doi = "10.1007/s10921-019-0606-5", issn = "1573-4862", journal = "Journal of Nondestructive Evaluation", month = "Jul", number = "3", pages = "68", title = "{V}isualization of the {R}olling {C}ontact {F}atigue {C}racks in {R}ail {T}racks with a {M}agnetooptical {S}ensor", url = "https://doi.org/10.1007/s10921-019-0606-5", volume = "38", year = "2019", }