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Jeong Whan Yoon - One of the best experts on this subject based on the ideXlab platform.
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correlation of the maximum shear stress with micro mechanisms of Ductile Fracture for metals with high strength to weight ratio
International Journal of Mechanical Sciences, 2018Co-Authors: Qi Chao, Jeong Whan Yoon, Junghan SongAbstract:Abstract Mechanisms of Ductile Fracture are investigated experimentally in a wide range of loading conditions from compressive upsetting to the balanced biaxial tension for two metals with high strength-to-density ratio of DP980 (t1.2) steel sheets and a bulk aluminum alloy of AA7075. Specimens are carefully designed to achieve various loading conditions from shear at low stress triaxiality to the balanced biaxial tension at high stress triaxiality for DP980, while both tensile and compressive tests are conducted for AA7075. Fractured specimen surfaces are analyzed macroscopically focusing on their relations with the maximum shear stress. It is observed that all the specimens tend to fail along the direction of the maximum shear stress in various loading states of plane strain compression, uniaxial compression, shear, uniaxial tension, plane strain tension and the balanced biaxial tension. Scanning electron microscope analyses of Fracture surfaces are also conducted to explore the underlying mechanism of void coalescence since coalescence of voids is viewed as the last step of Ductile Fracture after nucleation and growth of voids. It is noted that Fractured voids elongate along the direction of the maximum shear stress for all specimens with the stress triaxiality ranging from about −0.57 in compression to 0.67 in the balanced biaxial tension. The experiments of DP980 and AA7075 reveal that Ductile Fracture takes place along the direction of the maximum shear stress in the wide loading conditions of compressive upsetting, shear, uniaxial tension, plane strain tension and the balanced biaxial tension with stress triaxiality below 0.67. Thus, Ductile Fracture is expected to be governed by the maximum shear stress in these wide loading conditions of compression, shear and tension. It is suggested that effect of the maximum shear stress must be correctly coupled in modeling of Ductile Fracture in these loading conditions with uncoupled and coupled Ductile Fracture criteria.
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Anisotropic Ductile Fracture criterion based on linear transformation
International Journal of Plasticity, 2017Co-Authors: Jeong Whan YoonAbstract:Abstract An anisotropic Ductile Fracture criterion is proposed for Ductile Fracture of lightweight metals. The Ductile Fracture criterion couples effect of stress triaxiality on void growth, and assumes the shear linking-up of voids governed by the largest shear stress. The criterion is developed based on an isotropic strain rate potential computed from an isotropic damage equivalent strain rate vector, which is mapped from the plastic strain rate vector by a forth order linear transformation tensor. The proposed anisotropic Ductile Fracture criterion is applied to depict anisotropic Ductile Fracture of AA 6K21 in shear, uniaxial tension and plane strain tension along different loading directions, and the balanced biaxial tension. The predicted Fracture strain and Fracture locus are compared with experimental results for the verification of the proposed criterion. The comparison demonstrates that the Ductile Fracture criterion properly models the anisotropy in Ductile Fracture under shear, uniaxial tension, plane strain tension and balanced biaxial tension with high accuracy. It shows that the proposed anisotropic Ductile Fracture criterion can be utilized to predict the onset of Ductile Fracture in plastic deformation and metal forming of lightweight metals with approximately proportional loading.
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modeling of Ductile Fracture from shear to balanced biaxial tension for sheet metals
International Journal of Solids and Structures, 2017Co-Authors: Jeong Whan Yoon, Yanshan Lou, Lin Chen, Till Clausmeyer, Erman A TekkayaAbstract:Abstract A Ductile Fracture model is proposed to describe shear Fracture of sheet metals from shear to balanced biaxial tension via uniaxial and plane strain tension. The Fracture criterion models plastic damage as strain-induced void nucleation, triaxiality-governed void enlargement, Lode-controlled void torsion, and shear-restrained coalescence of voids. Its flexibility is investigated by a parameter study of the Ductile Fracture model proposed. The Fracture model is employed to describe Ductile Fracture behavior of an aluminum alloy AA6082 T6 (thickness: 1.0 mm). Dogbone specimens are strained to characterize the strain hardening properties, while another four different specimens are tested to characterize Fracture behavior in shear, uniaxial tension, plane strain tension and balanced biaxial tension. The loading processes are analyzed numerically with the stress invariant-based Drucker yield function which is for the first time specified for body-centered cubic and face-centered cubic metals. Fracture strains in various loading conditions are measured with a hybrid experimental-numerical approach. The measured Fracture strains are then used to calibrate the Ductile Fracture model proposed. The Ductile Fracture model calibrated above is employed to predict the onset of Ductile Fracture for these four specimens. For the purpose of comparison, the predicted Fracture strokes of these four loading conditions are compared with those predicted by the modified Mohr–Coulomb model ( Bai and Wierzbicki, 2008 ), and two micromechanism-inspired criteria proposed recently ( Lou et al., 2012 , Lou et al., 2014 ). The comparison reveals that the proposed model predicts the Fracture behavior in much better agreement compared with experimental results from shear to the balanced biaxial tension. Accordingly, the proposed Ductile Fracture criterion is recommended for the prediction of Ductile Fracture in sheet metal forming processes, optimization of forming parameters and design of tools for both solid elements and shell elements. Besides, the Ductile Fracture model proposed can also be applied in various bulk metal forming processes in case that the model is calibrated by proper sets of experiments.
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modeling of shear Ductile Fracture considering a changeable cut off value for stress triaxiality
International Journal of Plasticity, 2014Co-Authors: Jeong Whan YoonAbstract:Abstract A macroscopic Ductile Fracture criterion is proposed based on micro-mechanism analysis of nucleation, growth and shear coalescence of voids from experimental observation of Fracture surfaces. The proposed Ductile Fracture model endows a changeable cut-off value for the stress triaxiality to represent effect of micro-structures, the Lode parameter, temperature, and strain rate on ductility of metals. The proposed model is used to construct Fracture loci of AA 2024-T351. The constructed Fracture loci are compared with experimental data covering wide stress triaxiality ranging between −0.5 and 1.0. The Fracture loci are constructed in full stress spaces and plane stress conditions to analyze characteristics of the proposed Fracture loci. Errors of the equivalent stress to Fracture are calculated and compared with those predicted by the MSV model ( Khan and Liu, 2012a ) and series of the modified Mohr–Coulomb criteria. The comparison suggests that the proposed model can provide a satisfactory prediction of Ductile Fracture for metals from compressive upsetting tests to plane strain tension with slanted Fracture surfaces. Moreover, it is expected that the proposed model reasonably describes Ductile Fracture behavior in high velocity perforation simulation since a reasonable cut-off value for the stress triaxiality is coupled with the proposed Ductile Fracture criterion.
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modeling of shear Ductile Fracture considering a changeable cut off value for stress triaxiality
NUMISHEET 2014: The 9th International Conference and Workshop on Numerical Simulation of 3D Sheet Metal Forming Processes: Part A Benchmark Problems a, 2013Co-Authors: Jeong Whan YoonAbstract:A macroscopic Ductile Fracture criterion is proposed based on micro-mechanism analysis of nucleation, growth and shear coalescence of voids from experimental observation of Fracture surfaces. The proposed Ductile Fracture model endows a changeable cut-off value for the stress triaxiality to represent effect of micro-structures, the Lode parameter, temperature, and strain rate on ductility of metals. The proposed model is used to construct Fracture loci of AA 2024-T351. The constructed Fracture loci are compared with experimental data covering wide stress triaxiality ranging between −0.5 and 1.0. The comparison suggests that the proposed model can provide a satisfactory prediction of Ductile Fracture for metals from compressive upsetting tests to plane strain tension with slanted Fracture surfaces. Moreover, it is expected that the proposed model reasonably describes Ductile Fracture behavior in high velocity perforation simulation since a reasonable cut-off value for the stress triaxiality is coupled with...
Stephane J Marcadet - One of the best experts on this subject based on the ideXlab platform.
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critical hardening rate model for predicting path dependent Ductile Fracture
International Journal of Fracture, 2016Co-Authors: Stephane J Marcadet, Dirk MohrAbstract:A new phenomenological framework for predicting Ductile Fracture after non-proportional loading paths is proposed, implemented into FE software and validated experimentally for a limited set of monotonic and reverse loading conditions. Assuming that Ductile Fracture initiation is imminent with the formation of a shear band, a shear localization criterion in terms of the elastoplastic tangent matrix is sufficient from a theoretical point of view to predict Ductile Fracture after proportional and non-proportional loading. As a computationally efficient alternative to analyzing the acoustic tensor, a phenomenological criterion is proposed which expresses the equivalent hardening rate at the onset of Fracture as a function of the stress triaxiality and the Lode angle parameter. The mathematical form of the criterion is chosen such that it reduces to the Hosford–Coulomb criterion for proportional loading. The proposed framework implies that the plasticity model is responsible for the effect of loading history on Ductile Fracture. Important non-isotropic hardening features such as the Bauschinger effect, transient softening and hardening stagnation must be taken into account by the plasticity model formulation to obtain reasonable Fracture predictions after non-proportional loading histories. A new comprehensive plasticity model taking the above effects into account is thus an important byproduct of this work. In addition, compression–tension and reverse-shear experiments are performed on specimens extracted from dual-phase steel sheets to validate the proposed plasticity and Fracture model.
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micromechanically motivated phenomenological hosford coulomb model for predicting Ductile Fracture initiation at low stress triaxialities
International Journal of Solids and Structures, 2015Co-Authors: Dirk Mohr, Stephane J MarcadetAbstract:Abstract A phenomenological Ductile Fracture initiation model for metals is developed for predicting Ductile Fracture in industrial practice. Its formulation is based on the assumption that the onset of Fracture is imminent with the formation of a primary or secondary band of localization. The results from a unit cell analysis on a Levy–von Mises material with spherical defects revealed that a Mohr–Coulomb type of model is suitable for predicting the onset of shear and normal localization. To improve the agreement of the model predictions with experimental results, an extended Mohr–Coulomb criterion is proposed which makes use of the Hosford equivalent stress in combination with the normal stress acting on the plane of maximum shear. A Fracture initiation model is obtained by transforming the localization criterion from stress space to the space of equivalent plastic strain, stress triaxiality and Lode angle parameter using the material’s isotropic hardening law. Experimental results are presented for three different advanced high strength steels. For each material, the onset of Fracture is characterized for five distinct stress states including butterfly shear, notched tension, tension with a central hole and punch experiments. The comparison of model predictions with the experimental results demonstrates that the proposed Hosford–Coulomb model can predict the instant of Ductile Fracture initiation in advanced high strength steels with good accuracy.
Yanshan Lou - One of the best experts on this subject based on the ideXlab platform.
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modeling of Ductile Fracture from shear to balanced biaxial tension for sheet metals
International Journal of Solids and Structures, 2017Co-Authors: Jeong Whan Yoon, Yanshan Lou, Lin Chen, Till Clausmeyer, Erman A TekkayaAbstract:Abstract A Ductile Fracture model is proposed to describe shear Fracture of sheet metals from shear to balanced biaxial tension via uniaxial and plane strain tension. The Fracture criterion models plastic damage as strain-induced void nucleation, triaxiality-governed void enlargement, Lode-controlled void torsion, and shear-restrained coalescence of voids. Its flexibility is investigated by a parameter study of the Ductile Fracture model proposed. The Fracture model is employed to describe Ductile Fracture behavior of an aluminum alloy AA6082 T6 (thickness: 1.0 mm). Dogbone specimens are strained to characterize the strain hardening properties, while another four different specimens are tested to characterize Fracture behavior in shear, uniaxial tension, plane strain tension and balanced biaxial tension. The loading processes are analyzed numerically with the stress invariant-based Drucker yield function which is for the first time specified for body-centered cubic and face-centered cubic metals. Fracture strains in various loading conditions are measured with a hybrid experimental-numerical approach. The measured Fracture strains are then used to calibrate the Ductile Fracture model proposed. The Ductile Fracture model calibrated above is employed to predict the onset of Ductile Fracture for these four specimens. For the purpose of comparison, the predicted Fracture strokes of these four loading conditions are compared with those predicted by the modified Mohr–Coulomb model ( Bai and Wierzbicki, 2008 ), and two micromechanism-inspired criteria proposed recently ( Lou et al., 2012 , Lou et al., 2014 ). The comparison reveals that the proposed model predicts the Fracture behavior in much better agreement compared with experimental results from shear to the balanced biaxial tension. Accordingly, the proposed Ductile Fracture criterion is recommended for the prediction of Ductile Fracture in sheet metal forming processes, optimization of forming parameters and design of tools for both solid elements and shell elements. Besides, the Ductile Fracture model proposed can also be applied in various bulk metal forming processes in case that the model is calibrated by proper sets of experiments.
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prediction of Ductile Fracture for advanced high strength steel with a new criterion experiments and simulation
Journal of Materials Processing Technology, 2013Co-Authors: Yanshan Lou, Hoon HuhAbstract:Abstract This paper is concerned with prediction of the onset of Ductile Fracture by a newly proposed micro-mechanism-motivated macroscopic Ductile Fracture criterion in various stress states from shear to plane strain tension where most Ductile Fracture takes place in sheet metal forming processes. The new Ductile Fracture criterion ( Lou et al., 2012 ) is calibrated by the equivalent plastic strain to Fracture measured by the hybrid experimental–numerical method from four types of specimens manufactured from DP980 sheet whose Fracture locus is eventually constructed. The calibrated criterion is utilized to construct the Fracture locus of DP980. The constructed Fracture locus is then implemented into the ABAQUS/Explicit code to predict the onset of Ductile Fracture for these three types of specimens. Three types of notched specimens are further designed for the validation of the Ductile Fracture criterion from uniaxial tension to plane strain tension by comparison of experimental results to those numerically predicted by the Ductile Fracture criterion. Three types of shear specimens are then utilized to validate predictability of the Ductile Fracture criterion between shear and uniaxial tension. The validation demonstrates that the Ductile Fracture criterion can accurately predict the onset of Ductile Fracture for these specimens. The comparison result with high accuracy reveals that the criterion can correctly describe Ductile Fracture behaviors of metals in various stress states from shear to the plane strain tension.
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extension of a shear controlled Ductile Fracture model considering the stress triaxiality and the lode parameter
International Journal of Solids and Structures, 2013Co-Authors: Yanshan Lou, Hoon HuhAbstract:Abstract This paper is concerned with the extension of a shear-controlled Ductile Fracture criterion for accurate prediction of Fracture forming limit diagrams (FFLD) in sheet metal forming processes. A shear-controlled Ductile Fracture criterion is extended to a general three-dimensional stress space with dependence on the stress triaxiality and the Lode parameter. The underlying mechanisms of Lode parameter dependence of Ductile Fracture are first correlated to the effect of the maximum shear stress on shear-coalescence of voids. The effect of the stress triaxiality and the Lode parameter on the equivalent plastic strain to Fracture is investigated in the space of ( η , L , e ¯ ) . For the purpose of comparison, the Mohr–Coulomb criterion is also transformed into the space of ( η , L , e ¯ ) using the technique of the Mohr’s circles. Both criteria are applied to construct Fracture loci of Al 2024-T351. Fracture loci constructed are compared to experimental data points to validate the performance of two criteria. The comparison demonstrates that Fracture loci constructed by two criteria are close to experimental results except for two data points in the high stress triaxiality. The big difference between two criteria is that a cut-off value for the stress triaxiality is extremely small for the Mohr–Coulomb criterion while the new Ductile Fracture criterion endows a constant cut-off value of −1/3 which is reasonable for Ductile materials. Due to this limitation of the Mohr–Coulomb criterion, the new criterion is more suitable to model Ductile Fracture in metal forming processes.
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new Ductile Fracture criterion for prediction of Fracture forming limit diagrams of sheet metals
International Journal of Solids and Structures, 2012Co-Authors: Yanshan Lou, Hoon Huh, S. J. Lim, Keunhwan PackAbstract:Abstract A Ductile Fracture criterion is newly proposed to model Fracture behavior of sheet metals for nucleation, growth and shear coalescence of voids during plastic deformation. In the new Ductile Fracture criterion, void nucleation is described as a function of the equivalent plastic strain, void growth is a function of the stress triaxiality and void coalescence is controlled by the normalized maximal shear stress. The new Ductile Fracture criterion is applied to construct a Fracture forming limit diagram (FFLD) of a dual phase steel sheets of DP780 (1.0t). The FFLD is approximated using both the reverse engineering method and circle grid analysis (CGA) since DP780 fails with slight thickness reduction from the analysis of the Fracture surface. Predicted FFLDs are compared to experimental results to validate the performance of the new criterion in the intermediate stress triaxiality between 1/3 and 2/3. The new criterion is also applied to construct the Fracture locus of Al 2024-T351 ( Bao and Wierzbicki, 2004 ) to validate the performance of the new criterion in the low and negative stress triaxiality. The Fracture locus constructed by the new criterion are close to the experimental data points for all these two materials in a wide stress range from the uniaxial compression to the balanced biaxial tension. The new Ductile Fracture criterion is recommended to be utilized in finite element analysis to predict the onset of Ductile Fracture of sheet metals.
Hoon Huh - One of the best experts on this subject based on the ideXlab platform.
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prediction of Ductile Fracture for advanced high strength steel with a new criterion experiments and simulation
Journal of Materials Processing Technology, 2013Co-Authors: Yanshan Lou, Hoon HuhAbstract:Abstract This paper is concerned with prediction of the onset of Ductile Fracture by a newly proposed micro-mechanism-motivated macroscopic Ductile Fracture criterion in various stress states from shear to plane strain tension where most Ductile Fracture takes place in sheet metal forming processes. The new Ductile Fracture criterion ( Lou et al., 2012 ) is calibrated by the equivalent plastic strain to Fracture measured by the hybrid experimental–numerical method from four types of specimens manufactured from DP980 sheet whose Fracture locus is eventually constructed. The calibrated criterion is utilized to construct the Fracture locus of DP980. The constructed Fracture locus is then implemented into the ABAQUS/Explicit code to predict the onset of Ductile Fracture for these three types of specimens. Three types of notched specimens are further designed for the validation of the Ductile Fracture criterion from uniaxial tension to plane strain tension by comparison of experimental results to those numerically predicted by the Ductile Fracture criterion. Three types of shear specimens are then utilized to validate predictability of the Ductile Fracture criterion between shear and uniaxial tension. The validation demonstrates that the Ductile Fracture criterion can accurately predict the onset of Ductile Fracture for these specimens. The comparison result with high accuracy reveals that the criterion can correctly describe Ductile Fracture behaviors of metals in various stress states from shear to the plane strain tension.
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extension of a shear controlled Ductile Fracture model considering the stress triaxiality and the lode parameter
International Journal of Solids and Structures, 2013Co-Authors: Yanshan Lou, Hoon HuhAbstract:Abstract This paper is concerned with the extension of a shear-controlled Ductile Fracture criterion for accurate prediction of Fracture forming limit diagrams (FFLD) in sheet metal forming processes. A shear-controlled Ductile Fracture criterion is extended to a general three-dimensional stress space with dependence on the stress triaxiality and the Lode parameter. The underlying mechanisms of Lode parameter dependence of Ductile Fracture are first correlated to the effect of the maximum shear stress on shear-coalescence of voids. The effect of the stress triaxiality and the Lode parameter on the equivalent plastic strain to Fracture is investigated in the space of ( η , L , e ¯ ) . For the purpose of comparison, the Mohr–Coulomb criterion is also transformed into the space of ( η , L , e ¯ ) using the technique of the Mohr’s circles. Both criteria are applied to construct Fracture loci of Al 2024-T351. Fracture loci constructed are compared to experimental data points to validate the performance of two criteria. The comparison demonstrates that Fracture loci constructed by two criteria are close to experimental results except for two data points in the high stress triaxiality. The big difference between two criteria is that a cut-off value for the stress triaxiality is extremely small for the Mohr–Coulomb criterion while the new Ductile Fracture criterion endows a constant cut-off value of −1/3 which is reasonable for Ductile materials. Due to this limitation of the Mohr–Coulomb criterion, the new criterion is more suitable to model Ductile Fracture in metal forming processes.
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new Ductile Fracture criterion for prediction of Fracture forming limit diagrams of sheet metals
International Journal of Solids and Structures, 2012Co-Authors: Yanshan Lou, Hoon Huh, S. J. Lim, Keunhwan PackAbstract:Abstract A Ductile Fracture criterion is newly proposed to model Fracture behavior of sheet metals for nucleation, growth and shear coalescence of voids during plastic deformation. In the new Ductile Fracture criterion, void nucleation is described as a function of the equivalent plastic strain, void growth is a function of the stress triaxiality and void coalescence is controlled by the normalized maximal shear stress. The new Ductile Fracture criterion is applied to construct a Fracture forming limit diagram (FFLD) of a dual phase steel sheets of DP780 (1.0t). The FFLD is approximated using both the reverse engineering method and circle grid analysis (CGA) since DP780 fails with slight thickness reduction from the analysis of the Fracture surface. Predicted FFLDs are compared to experimental results to validate the performance of the new criterion in the intermediate stress triaxiality between 1/3 and 2/3. The new criterion is also applied to construct the Fracture locus of Al 2024-T351 ( Bao and Wierzbicki, 2004 ) to validate the performance of the new criterion in the low and negative stress triaxiality. The Fracture locus constructed by the new criterion are close to the experimental data points for all these two materials in a wide stress range from the uniaxial compression to the balanced biaxial tension. The new Ductile Fracture criterion is recommended to be utilized in finite element analysis to predict the onset of Ductile Fracture of sheet metals.
Dirk Mohr - One of the best experts on this subject based on the ideXlab platform.
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critical hardening rate model for predicting path dependent Ductile Fracture
International Journal of Fracture, 2016Co-Authors: Stephane J Marcadet, Dirk MohrAbstract:A new phenomenological framework for predicting Ductile Fracture after non-proportional loading paths is proposed, implemented into FE software and validated experimentally for a limited set of monotonic and reverse loading conditions. Assuming that Ductile Fracture initiation is imminent with the formation of a shear band, a shear localization criterion in terms of the elastoplastic tangent matrix is sufficient from a theoretical point of view to predict Ductile Fracture after proportional and non-proportional loading. As a computationally efficient alternative to analyzing the acoustic tensor, a phenomenological criterion is proposed which expresses the equivalent hardening rate at the onset of Fracture as a function of the stress triaxiality and the Lode angle parameter. The mathematical form of the criterion is chosen such that it reduces to the Hosford–Coulomb criterion for proportional loading. The proposed framework implies that the plasticity model is responsible for the effect of loading history on Ductile Fracture. Important non-isotropic hardening features such as the Bauschinger effect, transient softening and hardening stagnation must be taken into account by the plasticity model formulation to obtain reasonable Fracture predictions after non-proportional loading histories. A new comprehensive plasticity model taking the above effects into account is thus an important byproduct of this work. In addition, compression–tension and reverse-shear experiments are performed on specimens extracted from dual-phase steel sheets to validate the proposed plasticity and Fracture model.
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micromechanically motivated phenomenological hosford coulomb model for predicting Ductile Fracture initiation at low stress triaxialities
International Journal of Solids and Structures, 2015Co-Authors: Dirk Mohr, Stephane J MarcadetAbstract:Abstract A phenomenological Ductile Fracture initiation model for metals is developed for predicting Ductile Fracture in industrial practice. Its formulation is based on the assumption that the onset of Fracture is imminent with the formation of a primary or secondary band of localization. The results from a unit cell analysis on a Levy–von Mises material with spherical defects revealed that a Mohr–Coulomb type of model is suitable for predicting the onset of shear and normal localization. To improve the agreement of the model predictions with experimental results, an extended Mohr–Coulomb criterion is proposed which makes use of the Hosford equivalent stress in combination with the normal stress acting on the plane of maximum shear. A Fracture initiation model is obtained by transforming the localization criterion from stress space to the space of equivalent plastic strain, stress triaxiality and Lode angle parameter using the material’s isotropic hardening law. Experimental results are presented for three different advanced high strength steels. For each material, the onset of Fracture is characterized for five distinct stress states including butterfly shear, notched tension, tension with a central hole and punch experiments. The comparison of model predictions with the experimental results demonstrates that the proposed Hosford–Coulomb model can predict the instant of Ductile Fracture initiation in advanced high strength steels with good accuracy.
