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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 24 Oct 2021 16:42:46 GMT2021-10-24T16:42:46ZInvestigation of ductility limits based on bifurcation theory coupled with continuum damage mechanics
http://hdl.handle.net/10985/10440
Investigation of ductility limits based on bifurcation theory coupled with continuum damage mechanics
BOUKTIR, Yasser; CHALAL, Hocine; HADDAD, Moussa; ABED-MERAIM, Farid
The ductility limits of an St14 steel are investigated using an elastic‒plastic‒damage model and bifurcation theory. An associative J2-flow theory of plasticity is coupled with damage within the framework of continuum damage mechanics. For strain localization prediction, the bifurcation analysis is adopted. Both the constitutive equations and the localization bifurcation criterion are implemented into the finite element code ABAQUS, within the framework of large strains and a fully three-dimensional formulation. The material parameters associated with the fully coupled elastic‒plastic‒damage model are calibrated based on experimental tensile tests together with an inverse identification procedure. The above-described approach allows the forming limit diagrams of the studied material to be determined, which are then compared with experimental measurements. A main conclusion of the current study is that the proposed approach is able to provide predictions that are in good agreement with experiments under the condition of accurate material parameter calibration. The latter requires a careful identification strategy based on both calibrated finite element simulations of tensile tests at large strains and appropriately selected necking measurements. The resulting approach represents a useful basis for setting up reliable ductility limit prediction tools as well as effective parameter identification strategies.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/104402016-01-01T00:00:00ZBOUKTIR, YasserCHALAL, HocineHADDAD, MoussaABED-MERAIM, FaridThe ductility limits of an St14 steel are investigated using an elastic‒plastic‒damage model and bifurcation theory. An associative J2-flow theory of plasticity is coupled with damage within the framework of continuum damage mechanics. For strain localization prediction, the bifurcation analysis is adopted. Both the constitutive equations and the localization bifurcation criterion are implemented into the finite element code ABAQUS, within the framework of large strains and a fully three-dimensional formulation. The material parameters associated with the fully coupled elastic‒plastic‒damage model are calibrated based on experimental tensile tests together with an inverse identification procedure. The above-described approach allows the forming limit diagrams of the studied material to be determined, which are then compared with experimental measurements. A main conclusion of the current study is that the proposed approach is able to provide predictions that are in good agreement with experiments under the condition of accurate material parameter calibration. The latter requires a careful identification strategy based on both calibrated finite element simulations of tensile tests at large strains and appropriately selected necking measurements. The resulting approach represents a useful basis for setting up reliable ductility limit prediction tools as well as effective parameter identification strategies.Prediction of necking in thin sheet metals using an elastic‒plastic model coupled with ductile damage and bifurcation criteria
http://hdl.handle.net/10985/17483
Prediction of necking in thin sheet metals using an elastic‒plastic model coupled with ductile damage and bifurcation criteria
BOUKTIR, Yasser; CHALAL, Hocine; ABED-MERAIM, Farid
In this paper, the conditions for the occurrence of diffuse and localized necking in thin sheet metals are investigated. The prediction of these necking phenomena is undertaken using an elastic‒plastic model coupled with ductile damage, which is then combined with various plastic instability criteria based on bifurcation theory. The bifurcation criteria are first formulated within a general three-dimensional modeling framework, and then specialized to the particular case of plane-stress conditions. Some theoretical relationships or links between the different investigated bifurcation criteria are established, which allows a hierarchical classification in terms of their conservative character in predicting critical necking strains. The resulting numerical tool is implemented into the finite element code ABAQUS/Standard to predict forming limit diagrams (FLDs), in both situations of a fully three-dimensional formulation and a plane-stress framework. The proposed approach is then applied to the prediction of diffuse and localized necking for a DC06 mild steel material. The predicted FLDs confirm the above-established theoretical classification, revealing that the general bifurcation criterion provides a lower bound for diffuse necking prediction, while the loss of ellipticity criterion represents an upper bound for localized necking prediction. Some numerical aspects related to the prestrain effect on the development of necking are also investigated, which demonstrates the capability of the present approach in capturing the strain-path changes commonly encountered in complex sheet metal forming operations.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10985/174832018-01-01T00:00:00ZBOUKTIR, YasserCHALAL, HocineABED-MERAIM, FaridIn this paper, the conditions for the occurrence of diffuse and localized necking in thin sheet metals are investigated. The prediction of these necking phenomena is undertaken using an elastic‒plastic model coupled with ductile damage, which is then combined with various plastic instability criteria based on bifurcation theory. The bifurcation criteria are first formulated within a general three-dimensional modeling framework, and then specialized to the particular case of plane-stress conditions. Some theoretical relationships or links between the different investigated bifurcation criteria are established, which allows a hierarchical classification in terms of their conservative character in predicting critical necking strains. The resulting numerical tool is implemented into the finite element code ABAQUS/Standard to predict forming limit diagrams (FLDs), in both situations of a fully three-dimensional formulation and a plane-stress framework. The proposed approach is then applied to the prediction of diffuse and localized necking for a DC06 mild steel material. The predicted FLDs confirm the above-established theoretical classification, revealing that the general bifurcation criterion provides a lower bound for diffuse necking prediction, while the loss of ellipticity criterion represents an upper bound for localized necking prediction. Some numerical aspects related to the prestrain effect on the development of necking are also investigated, which demonstrates the capability of the present approach in capturing the strain-path changes commonly encountered in complex sheet metal forming operations.Effect of hardening and damage parameters on the prediction of localized necking in thin sheet metals
http://hdl.handle.net/10985/20345
Effect of hardening and damage parameters on the prediction of localized necking in thin sheet metals
BOUKTIR, Yasser; CHALAL, Hocine; ABED-MERAIM, Farid
In this work, an elastic–plastic model with Hill’48 anisotropic yield surface is coupled with the continuum damage mechanics theory and combined with the bifurcation analysis, in order to predict strain localization in thin sheet metals. The resulting approach is implemented into the ABAQUS finite element code within the framework of large strains and plane-stress conditions. A sensitivity analysis with respect to hardening and damage parameters is carried out to identify the most influential parameters on strain localization predictions.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/203452016-01-01T00:00:00ZBOUKTIR, YasserCHALAL, HocineABED-MERAIM, FaridIn this work, an elastic–plastic model with Hill’48 anisotropic yield surface is coupled with the continuum damage mechanics theory and combined with the bifurcation analysis, in order to predict strain localization in thin sheet metals. The resulting approach is implemented into the ABAQUS finite element code within the framework of large strains and plane-stress conditions. A sensitivity analysis with respect to hardening and damage parameters is carried out to identify the most influential parameters on strain localization predictions.Formability prediction of ductile materials using a non-associative plasticity model and bifurcation-based criteria
http://hdl.handle.net/10985/20341
Formability prediction of ductile materials using a non-associative plasticity model and bifurcation-based criteria
BOUKTIR, Yasser; CHALAL, Hocine; ABED-MERAIM, Farid
Plastic instabilities such as diffuse or localized necking may occur during sheet metal forming processes, thus limiting sheet metal formability, which is detrimental to industry. The formability of sheet metals is usually characterized by the concept of forming limit diagram (FLD), which was first proposed by Keeler and Backofen and Goodwin . The FLD reports combinations of in-plane major and minor strains, thus delimiting the plane into two zones: a safe zone and a critical one located above the FLD. It remains however that the experimental determination of FLDs is difficult, time consuming and involving non-negligible costs. To overcome these drawbacks, significant efforts have been devoted in the literature to develop theoretical criteria able to predict the formability limits of sheet metals, which are associated with the occurrence of diffuse or localized necking. For reliable predictions of sheet metal formability, one of the requirements is to develop an integrated approach coupling advanced constitutive models, capable of accurately reproducing the key physical phenomena that occur during forming processes, with theoretically well-founded necking criteria. In this work, a non-associative elastic‒plastic model, with Hill'48 anisotropic plastic yield surface, is coupled with the continuum damage mechanics theory based on the Lemaitre isotropic damage model. The resulting constitutive model is then combined with four bifurcation-based criteria, namely: General Bifurcation (GB) and Limit-Point Bifurcation (LPB) , for the prediction of diffuse necking, and Loss of Ellipticity (LE) and Loss of Strong Ellipticity (LSE), for the prediction of localized necking. The complete approach is implemented into the finite element code ABAQUS/Standard, within the framework of large strains and plane-stress conditions. A comparative study of the above bifurcation criteria is carried out on a mild steel, in order to classify them with respect to their order of prediction of critical necking strains.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/203412016-01-01T00:00:00ZBOUKTIR, YasserCHALAL, HocineABED-MERAIM, FaridPlastic instabilities such as diffuse or localized necking may occur during sheet metal forming processes, thus limiting sheet metal formability, which is detrimental to industry. The formability of sheet metals is usually characterized by the concept of forming limit diagram (FLD), which was first proposed by Keeler and Backofen and Goodwin . The FLD reports combinations of in-plane major and minor strains, thus delimiting the plane into two zones: a safe zone and a critical one located above the FLD. It remains however that the experimental determination of FLDs is difficult, time consuming and involving non-negligible costs. To overcome these drawbacks, significant efforts have been devoted in the literature to develop theoretical criteria able to predict the formability limits of sheet metals, which are associated with the occurrence of diffuse or localized necking. For reliable predictions of sheet metal formability, one of the requirements is to develop an integrated approach coupling advanced constitutive models, capable of accurately reproducing the key physical phenomena that occur during forming processes, with theoretically well-founded necking criteria. In this work, a non-associative elastic‒plastic model, with Hill'48 anisotropic plastic yield surface, is coupled with the continuum damage mechanics theory based on the Lemaitre isotropic damage model. The resulting constitutive model is then combined with four bifurcation-based criteria, namely: General Bifurcation (GB) and Limit-Point Bifurcation (LPB) , for the prediction of diffuse necking, and Loss of Ellipticity (LE) and Loss of Strong Ellipticity (LSE), for the prediction of localized necking. The complete approach is implemented into the finite element code ABAQUS/Standard, within the framework of large strains and plane-stress conditions. A comparative study of the above bifurcation criteria is carried out on a mild steel, in order to classify them with respect to their order of prediction of critical necking strains.