The Experts below are selected from a list of 2703 Experts worldwide ranked by ideXlab platform
Heung Nam Han - One of the best experts on this subject based on the ideXlab platform.
-
A Microstructure-based Analysis for Transformation Induced Plasticity and Mechanically Induced Martensitic Transformation
'Elsevier BV', 2019Co-Authors: Heung Nam Han, Chang Gil Lee, Dw Suh, Sung-joon KomAbstract:The transformation-induced plasticity (TRIP) accompanying the mechanically induced martensitic transformation (MIMT) in metastable austenitic steel was analyzed with a microstructure-based computational model which takes into account void nucleation and growth. The kinetics of the martensitic transformation was modeled using the concept of variant selection, which considers that the probability of nucleation occurring at a given site can be derived for each martensitic variant as a function of the interaction energy between the Externally Applied Stress state and the lattice deformation based on the Kurdjumov-Sachs (K-S) orientation relationship. To consider the localization of the plastic flow in the deforming material, the increase in void nucleation due to the martensitic transformation and the void growth based on the Gurson-Tvergaard yield criterion were adopted. The plastic instability condition was employed to predict the ductility of metastable austenitic steel. The calculated results were compared with the experimental data measured for 301 stainless steel subjected to uniaxial tension. The major cause of the enhancement of the ductility in the TRIP-aided steel was discussed from the viewpoint of the effect of the TRIP strain and the phase-hardening due to the MIMT. In addition, the evolution of the crystallographic texture during deformation and phase transformation was predicted by using the combination of the proposed model and the crystal plasticity. (C) 2007 Elsevier B.V. All rights reserved.X1129sciescopu
-
Diffusion Controlled Transformation Plasticity of Steel under Externally Applied Stress
'Informa UK Limited', 2018Co-Authors: Heung Nam Han, Jae Kon Lee, Dw Suh, Sungjoon KimAbstract:The transformation plasticity of steel during phase transformation under external Stress was modelled on a migrating interface diffusion mechanism. Atomic diffusion along the migrating phase interface is assumed to cause transformation plasticity by an accelerated Coble creep. A creep equation on transformation plasticity is derived as a function of transformation rate, temperature and Externally Applied Stress. Predictions are compared with dilatometric measurements during the austenite-to-ferrite and ferrite-to-austenite transformation of steel under various levels of uniaxial compressive Stress. Good agreement was found between the calculated and experimental transformation strain. The model proposed also successfully describes the thermally activated behaviour of the transformation strain. The evaluated effective diffusion coefficients on the migrating interface are three to four orders of magnitude larger than those reported for stationary boundaries.X112423sciescopu
-
Crystal plasticity finite element modeling of mechanically induced martensitic transformation (MIMT) in metastable austenite
US, 2018Co-Authors: Mg Lee, Sj Kim, Heung Nam HanAbstract:A new crystal plasticity model incorporating the mechanically induced martensitic transformation in metastable austenitic steel has been formulated and implemented into the finite element analysis. The kinetics of martensite transformation is modeled by taking into consideration of a nucleation-controlled phenomenon, where each potential martensitic variant based on Kurdjumov-Sachs (KS) relationship has different nucleation probability as a function of the interaction energy between Externally Applied Stress and lattice deformation. Therefore, the transformed volume fractions are determined following selective variants given by the crystallographic orientation of austenitic matrix and Applied Stress in the frame of the crystal plasticity finite element. The developed finite element program is capable of considering the effect of volume change by the Bain deformation and the lattice-invariant shear during the martensitic transformation by effectively modifying the evolution of plastic deformation gradient of the conventional rate-dependent crystal plasticity finite element. The validation of the proposed model has been carried out by comparing with the experimentally measured data under simple loading conditions. Good agreements with the measurements for the Stress-strain responses, transformed martenstic volume fractions and the influence of strain rate on the deformation behavior will enable the model to be promising for the future applications to the real forming process of the TRIP aided steel. (C) 2009 Elsevier Ltd. All rights reserved.X1555
-
Diffusion Controlled Recrystallization and Grain Growth-induced Plasticity of Steel under Externally Applied Stress
'Informa UK Limited', 2018Co-Authors: Heung Nam Han, Dw Suh, Se-jong Kim, Miyoung Kim, Gyosung Kim, Sj KimAbstract:Permanent deformation, which occurs during recrystallization and grain growth under an Applied Stress much smaller than the yield Stress of the material, was observed by dilatometric measurement and modelled on the basis of a migrating grain boundary diffusion mechanism. The observation confirmed that the transformation-induced deformation accompanying the interface migration is described by migrating boundary-induced plasticity rather than internal Stress caused by volume change and plastic yielding. In the model, atomic diffusion along the migrating grain boundary was assumed to cause recrystallization and grain growth-induced plasticity. A constitutive equation for recrystallization and grain growth-induced plasticity was derived as a function of the grain growth rate, temperature and Externally Applied Stress. The predictions were compared with the dilatometric measurements made during recrystallization and grain growth of an extra low-carbon steel under various levels of uniaxial compressive Stress, with good agreement being found between the calculated permanent strain and the experimentally derived strain.X11109sciescopu
-
Crystal plasticity finite element modeling of mechanically induced martensitic transformation (MIMT) in metastable austenite
'Elsevier BV', 2018Co-Authors: Mg Lee, Sj Kim, Heung Nam HanAbstract:A new crystal plasticity model incorporating the mechanically induced martensitic transformation in metastable austenitic steel has been formulated and implemented into the finite element analysis. The kinetics of martensite transformation is modeled by taking into consideration of a nucleation-controlled phenomenon, where each potential martensitic variant based on Kurdjumov-Sachs (KS) relationship has different nucleation probability as a function of the interaction energy between Externally Applied Stress and lattice deformation. Therefore, the transformed volume fractions are determined following selective variants given by the crystallographic orientation of austenitic matrix and Applied Stress in the frame of the crystal plasticity finite element. The developed finite element program is capable of considering the effect of volume change by the Bain deformation and the lattice-invariant shear during the martensitic transformation by effectively modifying the evolution of plastic deformation gradient of the conventional rate-dependent crystal plasticity finite element. The validation of the proposed model has been carried out by comparing with the experimentally measured data under simple loading conditions. Good agreements with the measurements for the Stress-strain responses, transformed martenstic volume fractions and the influence of strain rate on the deformation behavior will enable the model to be promising for the future applications to the real forming process of the TRIP aided steel. (C) 2009 Elsevier Ltd. All rights reserved.X115555sciescopu
Sungjoon Kim - One of the best experts on this subject based on the ideXlab platform.
-
Diffusion Controlled Transformation Plasticity of Steel under Externally Applied Stress
'Informa UK Limited', 2018Co-Authors: Heung Nam Han, Jae Kon Lee, Dw Suh, Sungjoon KimAbstract:The transformation plasticity of steel during phase transformation under external Stress was modelled on a migrating interface diffusion mechanism. Atomic diffusion along the migrating phase interface is assumed to cause transformation plasticity by an accelerated Coble creep. A creep equation on transformation plasticity is derived as a function of transformation rate, temperature and Externally Applied Stress. Predictions are compared with dilatometric measurements during the austenite-to-ferrite and ferrite-to-austenite transformation of steel under various levels of uniaxial compressive Stress. Good agreement was found between the calculated and experimental transformation strain. The model proposed also successfully describes the thermally activated behaviour of the transformation strain. The evaluated effective diffusion coefficients on the migrating interface are three to four orders of magnitude larger than those reported for stationary boundaries.X112423sciescopu
-
crystal plasticity finite element modeling of mechanically induced martensitic transformation mimt in metastable austenite
International Journal of Plasticity, 2010Co-Authors: Myounggyu Lee, Sungjoon Kim, Heung Nam HanAbstract:Abstract A new crystal plasticity model incorporating the mechanically induced martensitic transformation in metastable austenitic steel has been formulated and implemented into the finite element analysis. The kinetics of martensite transformation is modeled by taking into consideration of a nucleation-controlled phenomenon, where each potential martensitic variant based on Kurdjumov–Sachs (KS) relationship has different nucleation probability as a function of the interaction energy between Externally Applied Stress and lattice deformation. Therefore, the transformed volume fractions are determined following selective variants given by the crystallographic orientation of austenitic matrix and Applied Stress in the frame of the crystal plasticity finite element. The developed finite element program is capable of considering the effect of volume change by the Bain deformation and the lattice-invariant shear during the martensitic transformation by effectively modifying the evolution of plastic deformation gradient of the conventional rate-dependent crystal plasticity finite element. The validation of the proposed model has been carried out by comparing with the experimentally measured data under simple loading conditions. Good agreements with the measurements for the Stress–strain responses, transformed martensitic volume fractions and the influence of strain rate on the deformation behavior will enable the model to be promising for the future applications to the real forming process of the TRIP aided steel.
-
a microstructure based analysis for transformation induced plasticity and mechanically induced martensitic transformation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Heung Nam Han, Dong-woo Suh, Chang Gil Lee, Sungjoon KimAbstract:Abstract The transformation-induced plasticity (TRIP) accompanying the mechanically induced martensitic transformation (MIMT) in metastable austenitic steel was analyzed with a microstructure-based computational model which takes into account void nucleation and growth. The kinetics of the martensitic transformation was modeled using the concept of variant selection, which considers that the probability of nucleation occurring at a given site can be derived for each martensitic variant as a function of the interaction energy between the Externally Applied Stress state and the lattice deformation based on the Kurdjumov–Sachs (K–S) orientation relationship. To consider the localization of the plastic flow in the deforming material, the increase in void nucleation due to the martensitic transformation and the void growth based on the Gurson–Tvergaard yield criterion were adopted. The plastic instability condition was employed to predict the ductility of metastable austenitic steel. The calculated results were compared with the experimental data measured for 301 stainless steel subjected to uniaxial tension. The major cause of the enhancement of the ductility in the TRIP-aided steel was discussed from the viewpoint of the effect of the TRIP strain and the phase-hardening due to the MIMT. In addition, the evolution of the crystallographic texture during deformation and phase transformation was predicted by using the combination of the proposed model and the crystal plasticity.
-
variant selection in mechanically induced martensitic transformation of metastable austenitic steel
Isij International, 2005Co-Authors: Seunghyun Lee, Dong-woo Suh, Heung Nam Han, Junyun Kang, Huchul Lee, Sungjoon KimAbstract:During martensite transformation, parent austenite usually has an orientation relationship with newly transformed martensite and thereby a crystallographic texture of the austenite has a great influence on a texture development in the inherited martensite. For a given orientation relationship, there are several equivalent orientations of the inherited phase, which is called variant. Table 1 shows the 24 variants for Kurdjumov–Sachs (K–S) orientation relationship which is usually observed in carbon steels. In idealized case, all variants can appear in an austenite grain with an equal probability during the transformation. However, it has been reported that some variants preferentially appeared during the transformation. In other words, some variants possibly have greater relative probability to be selected. This phenomenon, which is called variant selection, is known to have a significant effect on the texture development in the inherited phase. The slip system of parent phase, the grain boundary orientation and the existence of Stress have been known to affect the variant selection during the transformation and the development of transformation texture. As for the slip activity, the criterion of variant selection was imposed in terms of slip distribution and was Applied to diffusion-controlled transformation. Ray et al. reviewed the various kinds of transformation texture that is normally encountered in austenite-to-ferrite transformation in steel. As for the bainitic transformation in steel, the variant selection had been investigated by an experimental observation. Recently, present authors suggested that the probability for a nucleation site to really act during displacive transformation could be derived for each variant as a function of the mechanical interaction energy between Externally Applied Stress and lattice deformation based on the Kurdjumov–Sachs (K–S) relationship. In present study, the variant selection in mechanically induced martensitic transformation of metastable austenite is investigated with respect to the interaction between external Stress and lattice deformation of the transformation. The orientations of parent austenite and newly transformed martensite are measured for tensile and compressive deformation using electron back-scattered diffraction (EBSD). For an individual austenite grain, the orientation of 24 K–S variants are evaluated and compared with measured orientation of martensite. The interaction energy between Externally Applied Stress and lattice deformation is calculated for each 24 K–S variant and the probability of variant selection is assessed. The assessed probability is compared with the experimental results.
-
a model for deformation behavior and mechanically induced martensitic transformation of metastable austenitic steel
Acta Materialia, 2004Co-Authors: Heung Nam Han, Chang Gil Lee, Taeho Lee, Sungjoon KimAbstract:Abstract A microstructure-based computational model, which can describe the transformation-induced plasticity (TRIP) accompanying the mechanically induced martensitic transformation in metastable austenitic steel, was suggested. The martensitic transformation kinetics was assumed as a nucleation-controlled phenomenon. The probability, which the nucleation site would really act, was derived for each martensitic variant as a function of the interaction energy between Externally Applied Stress state and lattice deformation. The increase of nucleation site in the austenite due to the plastic deformation was formulated as the increase of the shear-band intersection. The permanent strain originated from the transformation of austenite into martensite was evaluated by assessing the difference of the nucleation rate of martensitic variants. A self-consistent model was employed to predict the deformation behavior of each phase in the steel. The model was then implemented in an iterative program based on the radial return method to simulate the deformation behavior of the steel under various Stress states. The calculated results were compared with the experimental data measured under the uniaxial tension and simple shear. In addition, when various external forces are acting, the resulting effect on the Ms temperature was calculated by the model and compared with the reported data.
Dong-woo Suh - One of the best experts on this subject based on the ideXlab platform.
-
a microstructure based analysis for transformation induced plasticity and mechanically induced martensitic transformation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Heung Nam Han, Dong-woo Suh, Chang Gil Lee, Sungjoon KimAbstract:Abstract The transformation-induced plasticity (TRIP) accompanying the mechanically induced martensitic transformation (MIMT) in metastable austenitic steel was analyzed with a microstructure-based computational model which takes into account void nucleation and growth. The kinetics of the martensitic transformation was modeled using the concept of variant selection, which considers that the probability of nucleation occurring at a given site can be derived for each martensitic variant as a function of the interaction energy between the Externally Applied Stress state and the lattice deformation based on the Kurdjumov–Sachs (K–S) orientation relationship. To consider the localization of the plastic flow in the deforming material, the increase in void nucleation due to the martensitic transformation and the void growth based on the Gurson–Tvergaard yield criterion were adopted. The plastic instability condition was employed to predict the ductility of metastable austenitic steel. The calculated results were compared with the experimental data measured for 301 stainless steel subjected to uniaxial tension. The major cause of the enhancement of the ductility in the TRIP-aided steel was discussed from the viewpoint of the effect of the TRIP strain and the phase-hardening due to the MIMT. In addition, the evolution of the crystallographic texture during deformation and phase transformation was predicted by using the combination of the proposed model and the crystal plasticity.
-
variant selection in mechanically induced martensitic transformation of metastable austenitic steel
Isij International, 2005Co-Authors: Seunghyun Lee, Dong-woo Suh, Heung Nam Han, Junyun Kang, Huchul Lee, Sungjoon KimAbstract:During martensite transformation, parent austenite usually has an orientation relationship with newly transformed martensite and thereby a crystallographic texture of the austenite has a great influence on a texture development in the inherited martensite. For a given orientation relationship, there are several equivalent orientations of the inherited phase, which is called variant. Table 1 shows the 24 variants for Kurdjumov–Sachs (K–S) orientation relationship which is usually observed in carbon steels. In idealized case, all variants can appear in an austenite grain with an equal probability during the transformation. However, it has been reported that some variants preferentially appeared during the transformation. In other words, some variants possibly have greater relative probability to be selected. This phenomenon, which is called variant selection, is known to have a significant effect on the texture development in the inherited phase. The slip system of parent phase, the grain boundary orientation and the existence of Stress have been known to affect the variant selection during the transformation and the development of transformation texture. As for the slip activity, the criterion of variant selection was imposed in terms of slip distribution and was Applied to diffusion-controlled transformation. Ray et al. reviewed the various kinds of transformation texture that is normally encountered in austenite-to-ferrite transformation in steel. As for the bainitic transformation in steel, the variant selection had been investigated by an experimental observation. Recently, present authors suggested that the probability for a nucleation site to really act during displacive transformation could be derived for each variant as a function of the mechanical interaction energy between Externally Applied Stress and lattice deformation based on the Kurdjumov–Sachs (K–S) relationship. In present study, the variant selection in mechanically induced martensitic transformation of metastable austenite is investigated with respect to the interaction between external Stress and lattice deformation of the transformation. The orientations of parent austenite and newly transformed martensite are measured for tensile and compressive deformation using electron back-scattered diffraction (EBSD). For an individual austenite grain, the orientation of 24 K–S variants are evaluated and compared with measured orientation of martensite. The interaction energy between Externally Applied Stress and lattice deformation is calculated for each 24 K–S variant and the probability of variant selection is assessed. The assessed probability is compared with the experimental results.
-
a model for transformation plasticity during bainite transformation of steel under external Stress
Acta Materialia, 2003Co-Authors: Heung Nam Han, Dong-woo SuhAbstract:A model, which can calculate the transformation strain components when steel transforms to bainite under an external Stress, is suggested. In the model, the change of the nucleation rate for each variant due to the Applied Stress during transformation is considered. To assess the difference of the nucleation rate for variants, the interaction energy between the lattice deformation of the variant and the Externally Applied Stress is calculated on the basis of Kurdjumov-Sachs (KS) orientation relationship. From the model, both the volumetric and deviatoric strains caused by bainite transformation can be simultaneously obtained. The calculation results are compared with the experimental dilatometric measurements under various uniaxial compressive Stresses. Good agreement is found between the calculated and experimental values of transformation strain.
Chang Gil Lee - One of the best experts on this subject based on the ideXlab platform.
-
A Microstructure-based Analysis for Transformation Induced Plasticity and Mechanically Induced Martensitic Transformation
'Elsevier BV', 2019Co-Authors: Heung Nam Han, Chang Gil Lee, Dw Suh, Sung-joon KomAbstract:The transformation-induced plasticity (TRIP) accompanying the mechanically induced martensitic transformation (MIMT) in metastable austenitic steel was analyzed with a microstructure-based computational model which takes into account void nucleation and growth. The kinetics of the martensitic transformation was modeled using the concept of variant selection, which considers that the probability of nucleation occurring at a given site can be derived for each martensitic variant as a function of the interaction energy between the Externally Applied Stress state and the lattice deformation based on the Kurdjumov-Sachs (K-S) orientation relationship. To consider the localization of the plastic flow in the deforming material, the increase in void nucleation due to the martensitic transformation and the void growth based on the Gurson-Tvergaard yield criterion were adopted. The plastic instability condition was employed to predict the ductility of metastable austenitic steel. The calculated results were compared with the experimental data measured for 301 stainless steel subjected to uniaxial tension. The major cause of the enhancement of the ductility in the TRIP-aided steel was discussed from the viewpoint of the effect of the TRIP strain and the phase-hardening due to the MIMT. In addition, the evolution of the crystallographic texture during deformation and phase transformation was predicted by using the combination of the proposed model and the crystal plasticity. (C) 2007 Elsevier B.V. All rights reserved.X1129sciescopu
-
a microstructure based analysis for transformation induced plasticity and mechanically induced martensitic transformation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Heung Nam Han, Dong-woo Suh, Chang Gil Lee, Sungjoon KimAbstract:Abstract The transformation-induced plasticity (TRIP) accompanying the mechanically induced martensitic transformation (MIMT) in metastable austenitic steel was analyzed with a microstructure-based computational model which takes into account void nucleation and growth. The kinetics of the martensitic transformation was modeled using the concept of variant selection, which considers that the probability of nucleation occurring at a given site can be derived for each martensitic variant as a function of the interaction energy between the Externally Applied Stress state and the lattice deformation based on the Kurdjumov–Sachs (K–S) orientation relationship. To consider the localization of the plastic flow in the deforming material, the increase in void nucleation due to the martensitic transformation and the void growth based on the Gurson–Tvergaard yield criterion were adopted. The plastic instability condition was employed to predict the ductility of metastable austenitic steel. The calculated results were compared with the experimental data measured for 301 stainless steel subjected to uniaxial tension. The major cause of the enhancement of the ductility in the TRIP-aided steel was discussed from the viewpoint of the effect of the TRIP strain and the phase-hardening due to the MIMT. In addition, the evolution of the crystallographic texture during deformation and phase transformation was predicted by using the combination of the proposed model and the crystal plasticity.
-
a model for deformation behavior and mechanically induced martensitic transformation of metastable austenitic steel
Acta Materialia, 2004Co-Authors: Heung Nam Han, Chang Gil Lee, Taeho Lee, Sungjoon KimAbstract:Abstract A microstructure-based computational model, which can describe the transformation-induced plasticity (TRIP) accompanying the mechanically induced martensitic transformation in metastable austenitic steel, was suggested. The martensitic transformation kinetics was assumed as a nucleation-controlled phenomenon. The probability, which the nucleation site would really act, was derived for each martensitic variant as a function of the interaction energy between Externally Applied Stress state and lattice deformation. The increase of nucleation site in the austenite due to the plastic deformation was formulated as the increase of the shear-band intersection. The permanent strain originated from the transformation of austenite into martensite was evaluated by assessing the difference of the nucleation rate of martensitic variants. A self-consistent model was employed to predict the deformation behavior of each phase in the steel. The model was then implemented in an iterative program based on the radial return method to simulate the deformation behavior of the steel under various Stress states. The calculated results were compared with the experimental data measured under the uniaxial tension and simple shear. In addition, when various external forces are acting, the resulting effect on the Ms temperature was calculated by the model and compared with the reported data.
Alessio Zaccone - One of the best experts on this subject based on the ideXlab platform.
-
plasticity in amorphous solids is mediated by topological defects in the displacement field
Physical Review Letters, 2021Co-Authors: Matteo Baggioli, Ivan Kriuchevskyi, Timothy W Sirk, Alessio ZacconeAbstract:The microscopic mechanism by which amorphous solids yield plastically under an Externally Applied Stress or deformation has remained elusive in spite of enormous research activity in recent years. Most approaches have attempted to identify atomic-scale structural ``defects'' or spatiotemporal correlations in the undeformed glass that may trigger plastic instability. In contrast, in this Letter we show that the topological defects that correlate with plastic instability can be identified, not in the static structure of the glass, but rather in the nonaffine displacement field under deformation. These dislocation-like topological defects (DTDs) can be quantitatively characterized in terms of Burgers circuits (and the resulting Burgers vectors) that are constructed on the microscopic nonaffine displacement field. We demonstrate that (i) DTDs are the manifestation of incompatibility of deformation in glasses as a result of violation of Cauchy-Born rules (nonaffinity); (ii) the resulting average Burgers vector displays peaks in correspondence of major plastic events, including a spectacular nonlocal peak at the yielding transition, which results from self-organization into shear bands due to the attractive interaction between antiparallel DTDs; and (iii) application of Schmid's law to the DTDs leads to prediction of shear bands at 45\ifmmode^\circ\else\textdegree\fi{} for uniaxial deformations, as widely observed in experiments and simulations.
