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Frederic Barlat - One of the best experts on this subject based on the ideXlab platform.
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numerical modeling for accurate prediction of strain localization in Hole Expansion of a steel sheet
International Journal of Solids and Structures, 2019Co-Authors: Jeongyeon Lee, Myounggyu Lee, Toshihiko Kuwabara, Kijung Lee, Frederic BarlatAbstract:Abstract The Hole Expansion of a low carbon steel sheet shows an interesting feature that localized thinning and subsequent crack initiation are observed inside the specimen, and not at the Hole edge as is typically expected. The present work investigated a numerical modeling approach to predict this localization behavior within the framework of a finite element (FE) analysis. Plastic anisotropy of the sheet was taken into account using the anisotropic yield functions Yld2000-2d and Yld2004-18p for the plane stress and three-dimensional elements, respectively. Careful examination of the FE model revealed that the influence of the out-of-plane stress is very small, suggesting that shell elements can be efficiently used in the analysis. The influence of friction was also found to be negligibly small. However, the constitutive description exhibited a significant influence in that even a slight change in the yield function parameters resulted in a considerable difference in the prediction. For this reason, several sets of parameters were obtained based on the different material properties, and their influences on the Hole Expansion simulation were analyzed. In particular, the prediction accuracy could be greatly improved when the yield function parameters were optimized such that the flow stresses and plastic strain rate ratios in uniaxial and plane strain states were well captured.
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material modeling of 6016 o and 6016 t4 aluminum alloy sheets and application to Hole Expansion forming simulation
International Journal of Plasticity, 2017Co-Authors: Toshihiko Kuwabara, Takahiro Mori, Mineo Asano, Tomoyuki Hakoyama, Frederic BarlatAbstract:Abstract This study investigates the influence of heat treatment on the anisotropic plastic deformation behaviors of 6016-O and 6016-T4 aluminum alloy sheets. The two material samples were fabricated from the same lot and, therefore, have the same grain size and crystallographic texture. Biaxial tensile tests using both cruciform and tubular specimens are performed for many proportional stress paths in the first quadrant of stress space. The test results reveal that the degree of differential hardening (DH) is much larger in 6016-T4 than in 6016-O. It is shown that the work contour shape of 6016-O is controlled by crystallographic texture, whereas that of 6016-T4 presumably depends on GP-zones as well. From the biaxial stress test data, an appropriate yield function for each material is determined and employed in the finite element analysis of the Hole Expansion forming process. It was found that the Yld2000-2d yield function provides proper material representations of the plastic behavior of both material samples in the sense that it correctly predicts the fracture or localized neck locations, which occurs in the Hole edge vicinity. For 6016-O, the thickness strain profile predicted with the Yld2000-2d yield function, which accounts for the DH of the material, is in better agreement with the experimental results than that obtained with the isotropic hardening model. For 6016-T4, the Yld2000-2d yield function with an exponent of 8 with the isotropic hardening assumption leads to a fair prediction of the experimental data. In order to enhance the accuracy of forming simulations for 6016-T4, it is necessary to develop a material model that is capable of reproducing the significant DH resulting from the GP-zones.
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correlations between nanoindentation hardness and macroscopic mechanical properties in dp980 steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Mark D Taylor, David K Matlock, Kyoo Sil Choi, Corrine Packard, Le Xu, Frederic BarlatAbstract:Nanoindentation measurements were obtained on eight commercially-produced DP980 dual-phase steels to quantify the hardness of the individual constituents, ferrite and martensite, in each steel. Each microstructure was also evaluated to determine grain size, martensite volume fraction (MVF), and retained austenite content. Nanoindentation hardnesses and quantitative microstructural measurements were correlated with tensile properties and performance in Hole Expansion tests to assess the importance of the individual constituent properties. Hole Expansion samples were prepared with both sheared edges produced by mechanical punching, and non-deformed edges produced by electric discharge machining (EDM). Average material hardness based on nanoindentation data correlated directly to Vickers hardness measurements, verifying the capability of the nanoindentation technique to produce data consistent with traditional hardness measurements. Yield strength (YS) correlated directly to ferrite hardness indicating that, for a similar MVF and microstructural morphology, the YS is controlled by the strength of the softer matrix phase (ferrite). Hole Expansion ratios (HER) on EDM samples decreased with an increase in both martensite and ferrite hardness, indicating that EDM HER values can be enhanced by softening both constituents. Punched-Hole HER values decreased with increasing martensite hardness and martensite-to-ferrite hardness ratio, but were independent of ferrite hardness, indicating that softening the martensite while increasing the ferrite hardness could produce a higher HER.
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experimental and theoretical formability analysis using strain and stress based forming limit diagram for advanced high strength steels
Materials & Design, 2013Co-Authors: Sansot Panich, Surasak Suranuntchai, Vitoon Uthaisangsuk, Frederic Barlat, Suwat JirathearanatAbstract:Abstract In this study, experimental and numerical analyses of Forming Limit Diagram (FLD) and Forming Limit Stress Diagram (FLSD) for two Advanced High Strength Steel (AHSS) sheets grade DP780 and TRIP780 were performed. Initially, the forming limit curves were experimentally determined by means of the Nakazima forming test. Subsequently, analytical calculations of both FLD and FLSD were carried out based on the Marciniak–Kuczinsky (M–K) model. Additionally, the FLSDs were calculated using the experimental FLD data for both investigated steels. Different yield criteria, namely, von Mises, Hill’s 48, and Barlat2000 (Yld2000-2d) were applied for describing plastic flow behavior of the AHS steels. Both Swift and modified Voce strain hardening laws were taken into account. Hereby, influences of the constitutive yield models on the numerically determined FLDs and FLSDs were studied regarding to those resulted from the experimental data. The obtained stress based forming limits were significantly affected by the yield criterion and hardening model. It was found that the forming limit curves calculated by the combination of the Yld2000-2d yield criterion and Swift hardening law were in better agreement with the experimental curves. Finally, Hole Expansion tests were conducted in order to verify the different failure criteria. It was shown that the stress based forming limit curves could more precisely describe the formability behavior of both high strength steel sheets than the strain based forming limit curves.
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Hole Expansion of twinning induced plasticity steel
Scripta Materialia, 2012Co-Authors: Frederic Barlat, Myounggyu LeeAbstract:Abstract Fracture in the Hole Expansion test for a high-Mn twinning-induced plasticity (TWIP) steel sheet sample was investigated. The test results showed that cracking always occurred along the rolling direction (RD). The fracture behavior of the material was rationalized in terms of strain-rate sensitivity, yield surface shape and damage-producing MnS stringers aligned along the RD. In addition, according to the macroscopic constitutive modeling results, work hardening was shown to be almost isotropic for this material.
Myounggyu Lee - One of the best experts on this subject based on the ideXlab platform.
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effect of plastic anisotropy and portevin le chatelier bands on Hole Expansion in aa7075 sheets in t6 and w tempers
Journal of Materials Processing Technology, 2021Co-Authors: Yumi Choi, Myounggyu Lee, Yannis P KorkolisAbstract:Abstract Influence of tempers on the Hole-Expansion formability of an AA7075 aluminum sheet is investigated for -T6 (as-received) and -W tempers (super saturated by the solution heat treatment followed by water quenching). The Hole is prepared by end-milling, to limit the effects of Hole preparation on the results and instead highlight the effects of material behavior. A flat-headed punch is used to expand the Hole, and digital image correlation captures the strain fields throughout the experiment. The results present that the Hole can expand by 70 % more in -W compared to -T6 temper with the lower forming force. In contrast, thickness strain distribution around the Hole shows a similar pattern in both tempers except the observation of Portevin-Le Chatelier (PLC) effect in -W temper, which causing the inhomogeneous deformation. In parallel, the numerical simulation of the Hole-Expansion is performed using a user material subroutine implemented for the elasto-plastic material behavior, including plastic anisotropy, of both tempers. The predictions on the thickness strain variation and average level show good agreement with the experiment for -T6 temper, but less so for -W temper. This is shown to be the effect of PLC bands on the deformation: the material in -T6 temper is mainly governed by plastic anisotropy, but -W temper shows combined effect of plastic anisotropy and PLC bands. Nevertheless, the reasonable predictions of both tempers verify that the numerical framework established in this study can be used for preliminary, computationally-efficient virtual process design with a practical purpose, despite omitting the explicit physics of the PLC effect.
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practical microstructure informed dual scale simulation for predicting Hole Expansion failure of hyper burring steel
International Journal of Mechanical Sciences, 2019Co-Authors: Siwook Park, Myounggyu Lee, Jinwook Jung, Kyung Il Kim, Hwangsun Kim, Sungil Kim, Heung Nam HanAbstract:Abstract A practical dual-scale finite element model is developed to enable the formability prediction in the Hole Expansion of a hyper-burring steel sheet. This numerical approach resorts to the isotropic macroscale Hole Expansion simulation for calculating the deformation histories near the Hole edge, since they are known to be the potential fracture initiation site. The deformation histories are used as boundary conditions in the lower microscale model for calculating the local fracture of the steel sheet. The microscale simulation utilizes the dislocation density based constitutive model and a microstructure-based representative volume element (RVE), with realistic grain morphology taken from experimental microscopy. The fracture initiation at the Hole edge region is evaluated from the microscale simulation using four frequently employed uncoupled ductile fracture models, which enable the definition of the critical fracture strain. The proposed dual-scale model can better predict the failure initiation and location near the Hole edge when the modeling parameters are calibrated taking into account not only the deformation histories of the Hole edge, but also the local stress triaxiality. Moreover, the proposed dual-scale model is applied to analyze the microstructure effect on the Hole Expansion ratio by providing the insights into the effect of grain size and grain boundary characteristics.
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numerical modeling for accurate prediction of strain localization in Hole Expansion of a steel sheet
International Journal of Solids and Structures, 2019Co-Authors: Jeongyeon Lee, Myounggyu Lee, Toshihiko Kuwabara, Kijung Lee, Frederic BarlatAbstract:Abstract The Hole Expansion of a low carbon steel sheet shows an interesting feature that localized thinning and subsequent crack initiation are observed inside the specimen, and not at the Hole edge as is typically expected. The present work investigated a numerical modeling approach to predict this localization behavior within the framework of a finite element (FE) analysis. Plastic anisotropy of the sheet was taken into account using the anisotropic yield functions Yld2000-2d and Yld2004-18p for the plane stress and three-dimensional elements, respectively. Careful examination of the FE model revealed that the influence of the out-of-plane stress is very small, suggesting that shell elements can be efficiently used in the analysis. The influence of friction was also found to be negligibly small. However, the constitutive description exhibited a significant influence in that even a slight change in the yield function parameters resulted in a considerable difference in the prediction. For this reason, several sets of parameters were obtained based on the different material properties, and their influences on the Hole Expansion simulation were analyzed. In particular, the prediction accuracy could be greatly improved when the yield function parameters were optimized such that the flow stresses and plastic strain rate ratios in uniaxial and plane strain states were well captured.
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Hole Expansion of twinning induced plasticity steel
Scripta Materialia, 2012Co-Authors: Frederic Barlat, Myounggyu LeeAbstract:Abstract Fracture in the Hole Expansion test for a high-Mn twinning-induced plasticity (TWIP) steel sheet sample was investigated. The test results showed that cracking always occurred along the rolling direction (RD). The fracture behavior of the material was rationalized in terms of strain-rate sensitivity, yield surface shape and damage-producing MnS stringers aligned along the RD. In addition, according to the macroscopic constitutive modeling results, work hardening was shown to be almost isotropic for this material.
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Hole Expansion formability of dual phase steels using representative volume element approach with boundary smoothing technique
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010Co-Authors: Ji Hoon Kim, Myounggyu Lee, Dae Yong Kim, David K Matlock, R H WagonerAbstract:A qualitative analysis was carried out on the formability of dual-phase (DP) steels by introducing a realistic microstructure-based finite element approach. The present microstructure-based model was constructed using a mesh generation process with a boundary-smoothing algorithm after proper image processing. The developed model was applied to Hole-Expansion formability tests for DP steel sheets having different volume fractions and morphological features. On the basis of the microstructural inhomogeneity observed in the scanning electron micrographs of the DP steel sheets, it was inferred that the localized plastic deformation in the ferritic phase might be closely related to the macroscopic formability of DP steel. The experimentally observed difference between the Hole-Expansion formability of two different microstructures was reasonably explained by using the present finite element model.
Jeong Whan Yoon - One of the best experts on this subject based on the ideXlab platform.
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plastic anisotropy and failure in thin metal material characterization and fracture prediction with an advanced constitutive model and polar eps effective plastic strain fracture diagram for aa 3014 h19
International Journal of Solids and Structures, 2018Co-Authors: Jeong Whan Yoon, Robert E DickAbstract:Abstract Material characterizations for plasticity and fracture have been conducted from uniaxial tensile tests, bi-axial bulge test, and disk compression test for a beverage can AA3104-H19 material. The results from the experimental tests are used to determine material coefficients for the Yld2004-18p model ( Barlat et al., 2005 ). Finite element simulations are developed to evaluate the predicted earing profile. It is shown that the Yld2004-18p model is capable of accurately predicting the complex earing profile. Excellent agreement with the experimental data for eight ears exhibited in AA3014-H19 is achieved using the Yld2004-18p constitutive model. Further mechanical tests are also conducted on the AA3104-H19 to generate fracture data under different stress triaxiality conditions. Tensile tests are performed on the samples with a central Hole and notched specimens to achieve tensile and plane-strain conditions. A specially designed torsion test of a double bridge specimen is conducted to generate the points near pure shear conditions. The Nakajima test is also utilized to produce a bi-axial tension condition. The data from the experiments is used to generate the fracture locus in the principal strain space. Mapping from the principal strain space to stress triaxiality space, principal stress space, and Polar Effective Plastic Strain (PEPS) space is accomplished for a general yield function. Finite element modeling is used to validate the fracture diagram in the polar space. A model of a Hole Expansion during cup drawing demonstrates the robustness of the PEPS fracture theory for a condition with a highly anisotropic material and accurately predicts the direction for onset of failure.
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effect of anisotropic yield functions on the accuracy of Hole Expansion simulations
Journal of Materials Processing Technology, 2011Co-Authors: Toshihiko Kuwabara, Kazuma Hashimoto, Eiji Iizuka, Jeong Whan YoonAbstract:Abstract The deformation behavior of 780 MPa grade dual-phase steel sheet subjected to Hole Expansion is investigated both experimentally and analytically to clarify the effect of the material model (anisotropic yield function) on the predictive accuracy of finite element analysis of Hole Expansion. Biaxial tensile tests of the material were conducted; contours of plastic work and the directions of plastic strain rates are precisely measured and are in good agreement with those predicted from the Yld2000-2d yield function with an exponent of 4 ( Barlat et al., 2003 , Yoon et al., 2004 ). Finite element and experimental analyses on the Hole Expansion of the material were conducted. The Yld2000-2d yield function with an exponent of 4 provides closer agreement with the experimental results than other yield functions. Consequently, the anisotropic yield functions significantly affect the predictive accuracy of the deformation behavior of the steel sheet subjected to Hole Expansion, and the biaxial tensile test is effective for identification of the appropriate anisotropic yield function to be used for Hole Expansion simulation.
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effect of anisotropic yield functions on the accuracy of Hole Expansion simulations for 590 mpa grade steel sheet
Tetsu To Hagane-journal of The Iron and Steel Institute of Japan, 2010Co-Authors: Kazuma Hashimoto, Eiji Iizuka, Toshihiko Kuwbara, Jeong Whan YoonAbstract:The deformation behavior of a high-strength steel alloy with a tensile strength of 590 MPa is investigated both experimentally and analytically to clarify the effect of the material model (anisotropic yield function) on the predictive accuracy of the finite element simulation of Hole Expansion. Biaxial tensile tests of the test material have been carried out. Measured contours of plastic work and the directions of plastic strain rates are found to be in good agreement with those predicted using the Yld2000-2d yield function with an exponent of 6. The anisotropy in uniaxial tensile flow stresses and r-values has been also in good agreement with those predicted by the Yld2000-2d yield function, as opposed to the previous study [T.Kuwabara, K.Hashimoto, E.Iizuka and J.-W.Yoon: J. Jpn. Soc. Technol. Plast., 50 (2009), 925]. Forming simulations of and experiments on the Hole Expansion of the test material have been carried out using the von Mises, Hill's quadratic and the Yld2000-2d yield functions with different exponents. The Yld2000-2d yield functions have given the closest agreement with the experimental results. Consequently, it is found that anisotropic yield functions significantly affect the predictive accuracy of the deformation behavior of an anisotropic sheet metal subjected to Hole Expansion and that the biaxial tensile test is effective in identifying a proper anisotropic yield function to be used in the Hole Expansion simulation.
Surajit Kumar Paul - One of the best experts on this subject based on the ideXlab platform.
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A critical review on Hole Expansion ratio
Materialia, 2020Co-Authors: Surajit Kumar PaulAbstract:Abstract Materials resistance to edge fracture in intricate shape forming is commonly quantified by Hole Expansion ratio (HER). Hole Expansion test is normally used to evaluate HER. To date, the governing factors of HER have not well understood regardless of its importance for automotive part manufacturing with advanced high-strength steels. The present paper comprehensively discussed the recent progress on HER, including fundamental deformation aspects, the effect of punch geometries, correlation with tensile properties, and the influence of microstructure. This reviewed work explains why HER is currently an essential topic of engineering research.
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The effect of deformation gradient on necking and failure in Hole Expansion test
Manufacturing letters, 2019Co-Authors: Surajit Kumar PaulAbstract:Abstract Hole Expansion ratio (HER) is widely used to represent stretch-flangeability of sheet metal. The state of stress at the edge of central Hole is uniaxial tensile in nature during Hole Expansion test (HET). The strain/deformation is uniform throughout the width of the sample prior to the commencement of necking in a tensile test specimen. However, finite element investigation confirms the presence of prominent strain/deformation gradient in HET sample. Only one free edge i.e. central Hole edge presents in HET sample. These two effects are responsible for the higher HER than the uniaxial tensile total elongation of the material.
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non linear correlation between uniaxial tensile properties and shear edge Hole Expansion ratio
Journal of Materials Engineering and Performance, 2014Co-Authors: Surajit Kumar PaulAbstract:Stretch flanging of steel sheets is an important formability issue for automobile industry. Finite element simulation study confirms that the edge of the Hole deforms in a uniaxial tensile manner during the Hole Expansion process. To understand the effect of various tensile properties on Hole Expansion ratio, current experimental data and collected data from published work have been used. Yield stress, ultimate tensile stress, coefficient of normal anisotropy, total elongation, and post uniform elongation are closely related to Hole Expansion ratio. A non-linear relationship between Hole Expansion ratio and tensile properties (ultimate tensile stress, coefficient of normal anisotropy, and total elongation) is developed in the present investigation.
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Prediction of Hole Expansion ratio for automotive grade steels
Computational Materials Science, 2014Co-Authors: Surajit Kumar Paul, Monideepa Mukherjee, Saurabh Kundu, Sanjay ChandraAbstract:Abstract The objective of this work is to characterize experimentally and predict analytically the Hole Expansion ratio of steel sheets from uniaxial tensile properties. Firstly, finite element analysis is performed to understand the deformation modes (i.e. stress state) at the edge of the Hole during its Expansion by a conical punch. Finite element simulation study confirms that during the Hole Expansion process, the edge of the Hole undergoes uniaxial tensile deformation. Secondly, a fracture based failure criterion is employed to predict the Hole Expansion ratio, considering that the test stop criteria of the Hole Expansion process is the formation of a through thickness crack. Next, a methodology is proposed to compute the true fracture strain during uniaxial tensile test, following which a model is proposed to predict the Hole Expansion ratio analytically from the true fracture strain. The proposed model is validated with eight different steel grades.
R Underhill - One of the best experts on this subject based on the ideXlab platform.
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effects of tempering temperature on tensile and Hole Expansion properties of a c mn steel
Journal of Materials Processing Technology, 2003Co-Authors: X Fang, Brian Ralph, P Evans, R UnderhillAbstract:Abstract Effects of tempering temperature on tensile and Hole Expansion properties in a dual-phase C–Mn steel were investigated. The ultimate tensile strength and yield strength decreased and elongations increased with an increase of tempering temperature. The Hole Expansion property increased significantly at the tempering temperature ranging from 200 to 300 °C and did not show significant difference when tempering temperatures were lower than 200 °C or higher than 300 °C. The relationship between the Hole Expansion property and microstructural evolution has also been discussed.
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The relationships between tensile properties and Hole Expansion property of C-Mn steels
Journal of Materials Science, 2003Co-Authors: X Fang, Brian Ralph, P Evans, Z. Fan, R UnderhillAbstract:In order to investigate the effects of the microstructure and chemical compositions on the Hole Expansion property of C-Mn steels, four C-Mn steels were used and heat treated into different structures. The influences of the tensile properties on the Hole Expansion property were also investigated. It has been found in this paper that C-Mn steels with a high ratio of yield strength to ultimate tensile strength usually have a good Hole Expansion property. A high silicon content in solid solution can improve the Hole Expansion property. Carbon has a significant detrimental effect on the Hole Expansion property.