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Zhanqiang Liu - One of the best experts on this subject based on the ideXlab platform.
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A quantitative analysis of the transition of fracture mechanisms of Ti6Al4V over a wide range of Stress Triaxiality and strain rate
Engineering Fracture Mechanics, 2020Co-Authors: Bing Wang, Xinran Xiao, Viktor P. Astakhov, Zhanqiang LiuAbstract:Abstract The material fracture behavior and associated mechanism is known to be affected by the Stress state and strain rate. Using a recently developed rectangular hat-shaped specimen, the fracture behavior of Ti6Al4V was investigated with a Stress Triaxiality varying from −0.31 to 0.50 at strain rates ranging from quasi-static to 104 /s. The fracture mechanisms of Ti6Al4V under these conditions were studied at micro-scale through observations of cross-sectional microstructure and quantitative analysis of fracture surface morphology. It was found that λ, a parameter defining the percentage of equiaxed dimples on the fracture surface, shows a close correlation with the observed fracture mechanism. Therefore, a λ based criterion based has been introduced in this work to quantitatively describe the transition of fracture mechanisms. It was observed that the embrittlement of Ti6Al4V was promoted by a higher strain rate or a larger positive Stress Triaxiality, as expected. However, the Stress Triaxiality appeared to play a more dominant role. At sufficiently high negative or positive Stress Triaxiality values, the effect of strain rate on fracture mechanism became negligible.
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The effects of Stress Triaxiality and strain rate on the fracture strain of Ti6Al4V
Engineering Fracture Mechanics, 2019Co-Authors: Bing Wang, Xinran Xiao, Viktor P. Astakhov, Zhanqiang LiuAbstract:Abstract The fracture strain is known to be affected by the Stress state and strain rate. To measure the fracture strain over a wide range of Stress Triaxiality and strain rate, a rectangular hat-shaped specimen is designed. This specimen can be tested at low rates with a conventional load frame and at high rates with a Split Hopkinson Pressure Bar (SHPB). The specimen’s flat face facilitates the use of Digital Image Correlation (DIC) technique. The fracture strain of Ti6Al4V was determined for a Stress Triaxiality varying from −0.31 to 0.50 at strain rates ranging from quasi-static to 103/s. The results indicate that the fracture strain decreased with increasing either the Stress Triaxiality or the strain rate. A fracture strain model incorporating the effects of Stress Triaxiality and strain rate was established.
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evaluation on fracture locus of serrated chip generation with Stress Triaxiality in high speed machining of ti6al4v
Materials & Design, 2016Co-Authors: Bing Wang, Zhanqiang LiuAbstract:Abstract Stress Triaxiality has attracted wide attention in the research of material deformation and fracture behavior. This paper aims at exploring the effects of Stress Triaxiality on serrated chip fracture during high speed machining (HSM) of titanium alloy Ti6Al4V. Firstly, the models of normal Stress and Stress Triaxiality distributions are presented to describe the Stress state along the adiabatic shear band (ASB) of serrated chips generated in HSM of Ti6Al4V. The material fracture in ASB is extracted as the material failure problem under the combined loads of constant shear Stress with gradient tensile/compressive Stress. Secondly, a modified Bao-Wierzbicki fracture strain model is developed to predict the serrated chip fracture which considers the effects of strain rate and temperature. The equivalent fracture strain predicted with the modified Bao-Wierzbicki model is found to be more accurate than the original Bao-Wierzbicki model. At last, the fracture loci of ASBs in serrated chips for Ti6Al4V under different cutting speeds have been determined and validated by HSM experiments. The influences of stain rate and temperature on the material fracture strain have also been discussed. The research proves that the Stress Triaxiality plays a vital role in serrated chip formation during HSM.
Bing Wang - One of the best experts on this subject based on the ideXlab platform.
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A quantitative analysis of the transition of fracture mechanisms of Ti6Al4V over a wide range of Stress Triaxiality and strain rate
Engineering Fracture Mechanics, 2020Co-Authors: Bing Wang, Xinran Xiao, Viktor P. Astakhov, Zhanqiang LiuAbstract:Abstract The material fracture behavior and associated mechanism is known to be affected by the Stress state and strain rate. Using a recently developed rectangular hat-shaped specimen, the fracture behavior of Ti6Al4V was investigated with a Stress Triaxiality varying from −0.31 to 0.50 at strain rates ranging from quasi-static to 104 /s. The fracture mechanisms of Ti6Al4V under these conditions were studied at micro-scale through observations of cross-sectional microstructure and quantitative analysis of fracture surface morphology. It was found that λ, a parameter defining the percentage of equiaxed dimples on the fracture surface, shows a close correlation with the observed fracture mechanism. Therefore, a λ based criterion based has been introduced in this work to quantitatively describe the transition of fracture mechanisms. It was observed that the embrittlement of Ti6Al4V was promoted by a higher strain rate or a larger positive Stress Triaxiality, as expected. However, the Stress Triaxiality appeared to play a more dominant role. At sufficiently high negative or positive Stress Triaxiality values, the effect of strain rate on fracture mechanism became negligible.
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The effects of Stress Triaxiality and strain rate on the fracture strain of Ti6Al4V
Engineering Fracture Mechanics, 2019Co-Authors: Bing Wang, Xinran Xiao, Viktor P. Astakhov, Zhanqiang LiuAbstract:Abstract The fracture strain is known to be affected by the Stress state and strain rate. To measure the fracture strain over a wide range of Stress Triaxiality and strain rate, a rectangular hat-shaped specimen is designed. This specimen can be tested at low rates with a conventional load frame and at high rates with a Split Hopkinson Pressure Bar (SHPB). The specimen’s flat face facilitates the use of Digital Image Correlation (DIC) technique. The fracture strain of Ti6Al4V was determined for a Stress Triaxiality varying from −0.31 to 0.50 at strain rates ranging from quasi-static to 103/s. The results indicate that the fracture strain decreased with increasing either the Stress Triaxiality or the strain rate. A fracture strain model incorporating the effects of Stress Triaxiality and strain rate was established.
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evaluation on fracture locus of serrated chip generation with Stress Triaxiality in high speed machining of ti6al4v
Materials & Design, 2016Co-Authors: Bing Wang, Zhanqiang LiuAbstract:Abstract Stress Triaxiality has attracted wide attention in the research of material deformation and fracture behavior. This paper aims at exploring the effects of Stress Triaxiality on serrated chip fracture during high speed machining (HSM) of titanium alloy Ti6Al4V. Firstly, the models of normal Stress and Stress Triaxiality distributions are presented to describe the Stress state along the adiabatic shear band (ASB) of serrated chips generated in HSM of Ti6Al4V. The material fracture in ASB is extracted as the material failure problem under the combined loads of constant shear Stress with gradient tensile/compressive Stress. Secondly, a modified Bao-Wierzbicki fracture strain model is developed to predict the serrated chip fracture which considers the effects of strain rate and temperature. The equivalent fracture strain predicted with the modified Bao-Wierzbicki model is found to be more accurate than the original Bao-Wierzbicki model. At last, the fracture loci of ASBs in serrated chips for Ti6Al4V under different cutting speeds have been determined and validated by HSM experiments. The influences of stain rate and temperature on the material fracture strain have also been discussed. The research proves that the Stress Triaxiality plays a vital role in serrated chip formation during HSM.
Helmut Klöcker - One of the best experts on this subject based on the ideXlab platform.
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Metal ductility at low Stress Triaxiality application to sheet trimming
Journal of Materials Processing Technology, 2008Co-Authors: Alexis Bacha, Dominique Daniel, Helmut KlöckerAbstract:The growth and coalescence of voids nucleated by decohesion or cracking of second phase particles is a common damage process for many metallic alloys. Classical damage models, based on void growth and coalescence, predict a ductility increase if the Stress Triaxiality is decreased. But experiments show that the material ductility decreases at very low Stress triaxialities typical of sheet metal forming operations. At very low Stress Triaxiality no void growth is observed in metals containing second phase particles. In the present work, a new damage model for metals containing second phase particles submitted to low Stress Triaxiality loading is proposed
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Metal ductility at low Stress Triaxiality application to sheet trimming
Journal of Materials Processing Technology, 2008Co-Authors: Alexis Bacha, Dominique Daniel, Helmut KlöckerAbstract:International audienceThe growth and coalescence of voids nucleated by decohesion or cracking of second phase particles is a common damage process for many metallic alloys. Classical damage models, based on void growth and coalescence, predict a ductility increase if the Stress Triaxiality is decreased. But experiments show that the material ductility decreases at very low Stress triaxialities typical of sheet metal forming operations. At very low Stress Triaxiality no void growth is observed in metals containing second phase particles. In the present work, a new damage model for metals containing second phase particles submitted to low Stress Triaxiality loading is propose
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Metal ductility at low Stress Triaxiality application to sheet trimming
Journal of Materials Processing Technology, 2007Co-Authors: Alexis Bacha, Dominique Daniel, Helmut KlöckerAbstract:Abstract The growth and coalescence of voids nucleated by decohesion or cracking of second phase particles is a common damage process for many metallic alloys. Classical damage models, based on void growth and coalescence, predict a ductility increase if the Stress Triaxiality is decreased. But experiments show that the material ductility decreases at very low Stress triaxialities typical of sheet metal forming operations. At very low Stress Triaxiality no void growth is observed in metals containing second phase particles. In the present work, a new damage model for metals containing second phase particles submitted to low Stress Triaxiality loading is proposed. The new model is based on the observed physical damage mechanism, i.e. strain localization by reducing the inter-particle spacing during large material rotations. A two step modelling strategy has been followed to determine the ductility at low Stress Triaxiality. In the first step Thomason's void coalescence model is extended to large material rotations and shearing. In the second step the principles of applying this model to damage nucleated at second phase particles are described. The large material rotations observed under low Stress Triaxiality loading lead to large changes in the microstructure. Thus, in the second step, first appropriate representative volume and material elements are determined and then the critical damage parameters. Finally, as an example, the trimming behaviour of two aluminium sheet alloys is analyzed by the new model and the model predictions shown to be in good agreement with the experimental data, in particular for the blade displacement to crack initiation. The main outcomes of this work are: (1) a void coalescence model valid at low Stress Triaxiality, (2) a damage criterion valid at small Stress Triaxiality and large material rotations, (3) a damage variable expressed in a simple closed form for materials containing second phase particles. The damage analysis in a small fixed volume with a representative microstructure (Eulerian approach) and the damage analysis in all the material elements of the considered structure are compared in detail. In trimming (or similar processes), the major contribution to damage the material movement bringing second phase particles closer together and the void growth may be neglected. This simplifies considerable the analysis.
Fu Jian - One of the best experts on this subject based on the ideXlab platform.
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Crack tip Stress Triaxiality in welded joints
Materials Science and Technology, 2000Co-Authors: Fu JianAbstract:The investigation of the crack tip Stress Triaxiality of welded joint containing a central crack in the weld metal whose yield strength and crack depth may be varied using an elasto plastic finite element methodunder plain strain, and reveal that the Stress Triaxiality ahead of crack tip tends to increase for under matched weld and decrease for over matched weld using the even matching case as a references and as the crack length reduced for a given specimen width, the Stress Triaxiality decrease accordingly and the effect of strength mis matching becomes more obvious, and these can be explained in terms of plastic deformation and strain hardening interaction between weld metal and base material.
Jeong Whan Yoon - One of the best experts on this subject based on the ideXlab platform.
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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...
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Modeling of shear ductile fracture considering a changeable cut-off value for Stress Triaxiality
2013Co-Authors: Yanshan Lou, Jeong Whan Yoon, Hoon HuhAbstract: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 the proposed ductile fracture criterion
