The Experts below are selected from a list of 2040 Experts worldwide ranked by ideXlab platform
Sunghak Lee - One of the best experts on this subject based on the ideXlab platform.
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Study of Bauschinger Effect of acicular ferrite and polygonal ferrite through ex-situ interrupted bending tests in API X80 linepipe steels
Scientific Reports, 2018Co-Authors: Dae Woong Kim, Seok Su Sohn, Wan-keun Kim, Ki-seok Kim, Sunghak LeeAbstract:Linepipe steels complexly consisted of low-temperature transformation microstructures of bainitic ferrite, granular bainite, and acicular ferrite (AF) as well as polygonal ferrite (PF) which individually affect the Bauschinger Effect occurring during the pipe-forming. In this study, microscopic analyses of electron back-scattered diffraction (EBSD) coupled with tension-compression and interrupted bending tests were performed for verification of the Bauschinger Effect of AF and PF working as major microstructures in single-phase- and two-phase-rolled API X80 steels, respectively. With respect to microstructural Effects on Bauschinger Effect, the reduction in mobile dislocation density during the flattening was smaller in the AF than in the PF. However, the dislocation pile-up at low-angle substructures and high-angle grain boundaries was more frequently observed, thereby leading to the higher back stress and Bauschinger Effect in the AF. Boundary kernel average misorientation (KAM) profile played a critical role in determining the Bauschinger Effect because they were closely related with the back stress. Thus, the Bauschinger Effect was higher in the single-phase-rolled steel than in the two-phase-rolled steel. The present ex-situ interrupted bending methods coupled with EBSD analyses are outstanding ones for the detailed explanation of Bauschinger Effect and provide an important idea for the yield strength designs of linepipe steels.
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Effects of microstructure and pre strain on Bauschinger Effect in api x70 and x80 linepipe steels
Metals and Materials International, 2013Co-Authors: Seok Su Sohn, Seung Youb Han, Sang Yong Shin, Jin Ho Bae, Sunghak LeeAbstract:In this study, Effects of microstructure and pre-strain on the Bauschinger Effect were investigated in two API X70 and two API X80 linepipe steel sheets fabricated by controlling the cooling condition, and their yield strength and Bauschinger parameters were measured by the tension-compression test with varying tension pre-strain. The fast-cooled steels had the higher fraction of acicular ferrite, granular bainite and martensite-austenite (MA) constituents and smaller grain sizes. The reduction in yield stress (ΔYS) of the steels having a higher fraction of MA and smaller grain sizes was higher than that of the steels having a lower fraction of MA and larger grain sizes. The ΔYS was smallest at the pre-strain of 1%, reached the maximum at the pre-strain of 2%, and then decreased with increasing pre-strain. This result could be explained by the amounts of mobile dislocations and back stress, which affected the Bauschinger Effect and strain hardening Effect simultaneously. Since these two Effects affected the yield strength on a competing basis, the Bauschinger stress and hardening parameter were used to separately analyze these Effects. It could be confirmed that the Bauschinger Effect and strain hardening Effect were activated at pre-strains of 1–2% and 3–4%, respectively.
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Effects of microstructure and yield ratio on strain hardening and Bauschinger Effect in two api x80 linepipe steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012Co-Authors: Seung Youb Han, Seok Su Sohn, Sang Yong Shin, Jin Ho Bae, Hyoung Seop Kim, Sunghak LeeAbstract:Abstract In the present study, Effects of microstructure and yield ratio on strain hardening and Bauschinger Effect were investigated in two API X80 steel sheets fabricated by controlling the start cooling temperature. The steel whose start cooling temperature was lower had the higher fractions of granular bainite (GB) and martensite–austenite (MA) constituent and the lower fraction of acicular ferrite (AF), and showed the higher yield ratio. According to the results of the strain-reversal test composed of compressive and tensile tests at various compressive pre-strains, the reduction in yield strength of the steel having higher fractions of GB and MA was generally higher than that of the steel having lower fractions. This result could be explained by difference in density of mobile dislocations and by competing mechanisms between Bauschinger Effect and strain hardening, which were susceptible to the minute change in pre-strain during the piping process. When the pre-strain was low, e.g ., lower than 4%, the steels having low yield ratio and small Bauschinger Effect were desirable to minimize the reduction in yield strength.
Frederic Barlat - One of the best experts on this subject based on the ideXlab platform.
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mechanism of the Bauschinger Effect in al ge si alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Wei Gan, Hyuk Jong Bong, Hojun Lim, R K Boger, Frederic Barlat, R H WagonerAbstract:Abstract Wrought Al-Ge-Si alloys were designed and produced to ensure dislocation bypass strengthening (“hard pin” precipitates) without significant precipitate cutting/shearing (“soft pin” precipitates). These unusual alloys were processed from the melt, solution heat treated and aged. Aging curves at temperatures of 120, 160, 200 and 240 °C were established and the corresponding precipitate spacings, sizes, and morphologies were measured using TEM. The role of non-shearable precipitates in determining the magnitude of Bauschinger was revealed using large-strain compression/tension tests. The Effect of precipitates on the Bauschinger response was stronger than that of grain boundaries, even for these dilute alloys. The Bauschinger Effect increases dramatically from the under-aged to the peak aged condition and remains constant or decreases slowly through over-aging. This is consistent with reported behavior for Al-Cu alloys (maximum Effect at peak aging) and for other Al alloys (increasing through over-aging) such as Al-Cu-Li, Al 6111, Al 2524, and Al 6013. The Al-Ge-Si alloy response was simulated with three microstructural models, including a novel SD (SuperDislocation) model, to reveal the origins of the Bauschinger Effect in dilute precipitation-hardened / bypass alloys. The dominant mechanism is related to the elastic interaction of polarized dislocation arrays (generalized pile-up or bow-out model) at precipitate obstacles. Such Effects are ignored in continuum and crystal plasticity models.
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Crystal plasticity approach for predicting the Bauschinger Effect in dual-phase steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012Co-Authors: Frederic BarlatAbstract:Abstract A multi-scale micro-mechanical model was proposed to predict the cyclic behavior of dual-phase steels. The approach proposed in this study incorporates a simplified dislocation density model into the crystal plasticity finite element method (CP-FEM). The back stress resulting from dislocation pileups was used to reproduce the transient hardening behavior during load reversal. The simulations conducted using representative volume elements for the dual-phase steels lead to the following conclusions: (1) the large Bauschinger Effect (BE) and permanent softening in dual-phase steels originate primarily from the inhomogeneity due to the soft and hard phases; (2) the elastic incompatibility due to the grain orientation distribution generates some BE, but is not sufficient to explain the measured stress–strain curve; and (3) the inclusion of the back stress produced by the dislocation pileup can explain the strain hardening stagnation during reverse loading.
Seok Su Sohn - One of the best experts on this subject based on the ideXlab platform.
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Effects of microstructure and yield ratio on strain hardening and Bauschinger Effect in two API X80 linepipe steels
'SZTE Hungarian Scientific Society of the Silicate Industry', 2019Co-Authors: Seung Youb Han, Seok Su Sohn, Sang Yong Shin, Jin Ho Bae, Hs Kim, Lee S.Abstract:In the present study, Effects of microstructure and yield ratio on strain hardening and Bauschinger Effect were investigated in two API X80 steel sheets fabricated by controlling the start cooling temperature. The steel whose start cooling temperature was lower had the higher fractions of granular bainite (GB) and martensite-austenite (MA) constituent and the lower fraction of acicular ferrite (AF), and showed the higher yield ratio. According to the results of the strain-reversal test composed of compressive and tensile tests at various compressive pre-strains, the reduction in yield strength of the steel having higher fractions of GB and MA was generally higher than that of the steel having lower fractions. This result could be explained by difference in density of mobile dislocations and by competing mechanisms between Bauschinger Effect and strain hardening, which were susceptible to the minute change in pre-strain during the piping process. When the pre-strain was low, e.g., lower than 4%, the steels having low yield ratio and small Bauschinger Effect were desirable to minimize the reduction in yield strength. (C) 2012 Elsevier B.V. All rights reserved.X11
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Study of Bauschinger Effect of acicular ferrite and polygonal ferrite through ex-situ interrupted bending tests in API X80 linepipe steels
Scientific Reports, 2018Co-Authors: Dae Woong Kim, Seok Su Sohn, Wan-keun Kim, Ki-seok Kim, Sunghak LeeAbstract:Linepipe steels complexly consisted of low-temperature transformation microstructures of bainitic ferrite, granular bainite, and acicular ferrite (AF) as well as polygonal ferrite (PF) which individually affect the Bauschinger Effect occurring during the pipe-forming. In this study, microscopic analyses of electron back-scattered diffraction (EBSD) coupled with tension-compression and interrupted bending tests were performed for verification of the Bauschinger Effect of AF and PF working as major microstructures in single-phase- and two-phase-rolled API X80 steels, respectively. With respect to microstructural Effects on Bauschinger Effect, the reduction in mobile dislocation density during the flattening was smaller in the AF than in the PF. However, the dislocation pile-up at low-angle substructures and high-angle grain boundaries was more frequently observed, thereby leading to the higher back stress and Bauschinger Effect in the AF. Boundary kernel average misorientation (KAM) profile played a critical role in determining the Bauschinger Effect because they were closely related with the back stress. Thus, the Bauschinger Effect was higher in the single-phase-rolled steel than in the two-phase-rolled steel. The present ex-situ interrupted bending methods coupled with EBSD analyses are outstanding ones for the detailed explanation of Bauschinger Effect and provide an important idea for the yield strength designs of linepipe steels.
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Effects of microstructure and pre strain on Bauschinger Effect in api x70 and x80 linepipe steels
Metals and Materials International, 2013Co-Authors: Seok Su Sohn, Seung Youb Han, Sang Yong Shin, Jin Ho Bae, Sunghak LeeAbstract:In this study, Effects of microstructure and pre-strain on the Bauschinger Effect were investigated in two API X70 and two API X80 linepipe steel sheets fabricated by controlling the cooling condition, and their yield strength and Bauschinger parameters were measured by the tension-compression test with varying tension pre-strain. The fast-cooled steels had the higher fraction of acicular ferrite, granular bainite and martensite-austenite (MA) constituents and smaller grain sizes. The reduction in yield stress (ΔYS) of the steels having a higher fraction of MA and smaller grain sizes was higher than that of the steels having a lower fraction of MA and larger grain sizes. The ΔYS was smallest at the pre-strain of 1%, reached the maximum at the pre-strain of 2%, and then decreased with increasing pre-strain. This result could be explained by the amounts of mobile dislocations and back stress, which affected the Bauschinger Effect and strain hardening Effect simultaneously. Since these two Effects affected the yield strength on a competing basis, the Bauschinger stress and hardening parameter were used to separately analyze these Effects. It could be confirmed that the Bauschinger Effect and strain hardening Effect were activated at pre-strains of 1–2% and 3–4%, respectively.
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Effects of microstructure and yield ratio on strain hardening and Bauschinger Effect in two api x80 linepipe steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012Co-Authors: Seung Youb Han, Seok Su Sohn, Sang Yong Shin, Jin Ho Bae, Hyoung Seop Kim, Sunghak LeeAbstract:Abstract In the present study, Effects of microstructure and yield ratio on strain hardening and Bauschinger Effect were investigated in two API X80 steel sheets fabricated by controlling the start cooling temperature. The steel whose start cooling temperature was lower had the higher fractions of granular bainite (GB) and martensite–austenite (MA) constituent and the lower fraction of acicular ferrite (AF), and showed the higher yield ratio. According to the results of the strain-reversal test composed of compressive and tensile tests at various compressive pre-strains, the reduction in yield strength of the steel having higher fractions of GB and MA was generally higher than that of the steel having lower fractions. This result could be explained by difference in density of mobile dislocations and by competing mechanisms between Bauschinger Effect and strain hardening, which were susceptible to the minute change in pre-strain during the piping process. When the pre-strain was low, e.g ., lower than 4%, the steels having low yield ratio and small Bauschinger Effect were desirable to minimize the reduction in yield strength.
Seung Youb Han - One of the best experts on this subject based on the ideXlab platform.
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Effects of microstructure and yield ratio on strain hardening and Bauschinger Effect in two API X80 linepipe steels
'SZTE Hungarian Scientific Society of the Silicate Industry', 2019Co-Authors: Seung Youb Han, Seok Su Sohn, Sang Yong Shin, Jin Ho Bae, Hs Kim, Lee S.Abstract:In the present study, Effects of microstructure and yield ratio on strain hardening and Bauschinger Effect were investigated in two API X80 steel sheets fabricated by controlling the start cooling temperature. The steel whose start cooling temperature was lower had the higher fractions of granular bainite (GB) and martensite-austenite (MA) constituent and the lower fraction of acicular ferrite (AF), and showed the higher yield ratio. According to the results of the strain-reversal test composed of compressive and tensile tests at various compressive pre-strains, the reduction in yield strength of the steel having higher fractions of GB and MA was generally higher than that of the steel having lower fractions. This result could be explained by difference in density of mobile dislocations and by competing mechanisms between Bauschinger Effect and strain hardening, which were susceptible to the minute change in pre-strain during the piping process. When the pre-strain was low, e.g., lower than 4%, the steels having low yield ratio and small Bauschinger Effect were desirable to minimize the reduction in yield strength. (C) 2012 Elsevier B.V. All rights reserved.X11
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Effects of microstructure and pre strain on Bauschinger Effect in api x70 and x80 linepipe steels
Metals and Materials International, 2013Co-Authors: Seok Su Sohn, Seung Youb Han, Sang Yong Shin, Jin Ho Bae, Sunghak LeeAbstract:In this study, Effects of microstructure and pre-strain on the Bauschinger Effect were investigated in two API X70 and two API X80 linepipe steel sheets fabricated by controlling the cooling condition, and their yield strength and Bauschinger parameters were measured by the tension-compression test with varying tension pre-strain. The fast-cooled steels had the higher fraction of acicular ferrite, granular bainite and martensite-austenite (MA) constituents and smaller grain sizes. The reduction in yield stress (ΔYS) of the steels having a higher fraction of MA and smaller grain sizes was higher than that of the steels having a lower fraction of MA and larger grain sizes. The ΔYS was smallest at the pre-strain of 1%, reached the maximum at the pre-strain of 2%, and then decreased with increasing pre-strain. This result could be explained by the amounts of mobile dislocations and back stress, which affected the Bauschinger Effect and strain hardening Effect simultaneously. Since these two Effects affected the yield strength on a competing basis, the Bauschinger stress and hardening parameter were used to separately analyze these Effects. It could be confirmed that the Bauschinger Effect and strain hardening Effect were activated at pre-strains of 1–2% and 3–4%, respectively.
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Effects of microstructure and yield ratio on strain hardening and Bauschinger Effect in two api x80 linepipe steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012Co-Authors: Seung Youb Han, Seok Su Sohn, Sang Yong Shin, Jin Ho Bae, Hyoung Seop Kim, Sunghak LeeAbstract:Abstract In the present study, Effects of microstructure and yield ratio on strain hardening and Bauschinger Effect were investigated in two API X80 steel sheets fabricated by controlling the start cooling temperature. The steel whose start cooling temperature was lower had the higher fractions of granular bainite (GB) and martensite–austenite (MA) constituent and the lower fraction of acicular ferrite (AF), and showed the higher yield ratio. According to the results of the strain-reversal test composed of compressive and tensile tests at various compressive pre-strains, the reduction in yield strength of the steel having higher fractions of GB and MA was generally higher than that of the steel having lower fractions. This result could be explained by difference in density of mobile dislocations and by competing mechanisms between Bauschinger Effect and strain hardening, which were susceptible to the minute change in pre-strain during the piping process. When the pre-strain was low, e.g ., lower than 4%, the steels having low yield ratio and small Bauschinger Effect were desirable to minimize the reduction in yield strength.
Anthony P. Parker - One of the best experts on this subject based on the ideXlab platform.
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Charles Mossey Experimental Data, Numerical Fit and Fatigue Life Calculations Relating to the Bauschinger Effect in High Strength Armament Steels
2020Co-Authors: Edward Troiano, Anthony P. Parker, John UnderwoodAbstract:The uniaxial Bauschinger Effect has been evaluated in several high strength steels being considered for armament application. The steels investigated include ASTM A723 (1130 and 1330 MPa
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finite element investigation of Bauschinger Effect in high strength a723 pressure vessel steel
Journal of Pressure Vessel Technology-transactions of The Asme, 2006Co-Authors: Edward Troiano, John H. Underwood, Anthony P. ParkerAbstract:The Bauschinger Effect has been evaluated in high-strength pressure vessels. A simple initial test suggested that a biaxial Bauschinger Effect was present and that it was different from previously published uniaxial Bauschinger results. The difference was believed to be significant, so further investigation was undertaken. Several full-size A723 steel gun sections were heavily overstrained and subjected to slit tests in order to measure opening angles and displacements. These geometries were then modeled with finite element (FE) analysis using both ideal autofrettage stresses and Bauschinger modified stresses, which were based on previously published uniaxial Bauschinger test results. Because techniques available for predicting reverse yielding for overstrained pressure vessels were limited, a simple methodology for predicting the yield surface upon reverse yielding from a series of uniaxial Bauschinger test data was developed and is presented. This methodology, when used in the FE predictions, compares favorably with analytical predictions made previously. Comparisons of slit-opening results measured from pressure vessel sections with FE calculations using uniaxial Bauschinger data are made. The opening displacements comparison between the uniaxial predictions and those measured from the heavily overstrained sections with biaxial stresses are so subtle (<1 mm) that the tests appear to be inconclusive.
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a re autofrettage procedure for mitigation of Bauschinger Effect in thick cylinders
Journal of Pressure Vessel Technology-transactions of The Asme, 2004Co-Authors: Anthony P. ParkerAbstract:A manufacturing procedure for enhancing residual stresses and thereby improving fatigue lifetime and fracture resistance of pressure vessels is proposed. The procedure involves initial autofrettage; one or more ‘heat soak plus autofrettage’ sequences and an optional final heat soak. Stresses are calculated numerically for traditional, single autofrettage and compared with those created by the new procedure. The loss of bore compressive hoop stress due to Bauschinger Effect is predicted to be significantly reduced. Associated fatigue lifetime calculations indicate that life may be improved by a factor of between 2 and 30, depending upon tube geometry and the ratio of cyclic pressure to yield strength. Repeated overload plus heat soak cycles may also be of benefit in other engineering design scenarios.Copyright © 2005 by ASME
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characterization of steels using a revised kinematic hardening model incorporating Bauschinger Effect
Journal of Pressure Vessel Technology-transactions of The Asme, 2003Co-Authors: Anthony P. Parker, Edward Troiano, John H. Underwood, C MosseyAbstract:Abstract : A new variant of the nonlinear kinematic hardening model is proposed that accommodates both nonlinear and linear strain hardening during initial tensile loading and reduced elastic modulus during initial load reversal. It also incorporates the Bauschinger Effect, as a function of prior tensile plastic strain, during the nonlinear compressive loading phase. The model is shown to fit experimental data from a total of five candidate gun steels. The numerical fits will be employed in subsequent work to predict residual stresses and fatigue lifetimes for autofrettaged tubes manufactured from the candidate steels.
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experimental data numerical fit and fatigue life calculations relating to the Bauschinger Effect in high strength armament steels
Journal of Pressure Vessel Technology-transactions of The Asme, 2003Co-Authors: Edward Troiano, Anthony P. Parker, John H. Underwood, C MosseyAbstract:Abstract : The uniaxial Bauschinger Effect has been evaluated in several high strength steels being considered for armament use. Tests were conducted at plastic strains up to 3.5%. Results of testing show a progressive decrease in Bauschinger Effect up to plastic strains of approximately 1% (for all materials investigated), after which there is little further decrease.
