Recent studies indicate that the texture distribution in friction stir welded(FSW)Mg alloys can be tailored and hence improve the joint performance.In this work,a crystal plasticity finite element modeling(CPFEM)was p...Recent studies indicate that the texture distribution in friction stir welded(FSW)Mg alloys can be tailored and hence improve the joint performance.In this work,a crystal plasticity finite element modeling(CPFEM)was performed to understand the effects of texture distribution in stir zone(SZ)on the nonuniform plastic deformation and fracture localization.In total,six kinds of observed or purposely tilted texture distributions were modelled.The"concave-convex"appearance,as commonly observed in the tensile sample,was successfully simulated.It reveals that the mirror-symmetrical distribution of basal planes in the region of easy to activate basal slip(EABS)determined the"concave-convex"appearance in SZ-center.The asymmetrical appearance exchanged on plane A and plane B when the directions of basal planes were switched in the two EABS regions.Furthermore,the asymmetrical feature of plastic deformation was changed with varying the texture distribution in SZ.The"embossed"feature became more obvious in SZ-center first,and then gradually weakened with the c-axis rotated away from the weld plate plane.Severe necking was successfully simulated in SZ-center of FSW-H joint and in SZ-side of FSW-L joint.That might determine the observed fracture morphology.We believe that this simulation study is helpful for further improving the performance of FSW Mg joints.展开更多
A dynamic compression test was performed on α+β dual-phase titanium alloy Ti20C using a split Hopkinson pressure bar.The formation of adiabatic shear bands generated during the compression process was studied by com...A dynamic compression test was performed on α+β dual-phase titanium alloy Ti20C using a split Hopkinson pressure bar.The formation of adiabatic shear bands generated during the compression process was studied by combining the proposed multi-scale crystal plasticity finite element method with experimental measurements.The complex local micro region load was progressively extracted from the simulation results of a macro model and applied to an established three-dimensional multi-grain microstructure model.Subsequently,the evolution histories of the grain shape,size,and orientation inside the adiabatic shear band were quantitatively simulated.The results corresponded closely to the experimental results obtained via transmission electron microscopy and precession electron diffraction.Furthermore,by calculating the grain rotation and temperature rise inside the adiabatic shear band,the microstructural softening and thermal softening effects of typical heavily-deformed α grains were successfully decoupled.The results revealed that the microstructural softening stress was triggered and then stabilized(in general)at a relatively high value.This indicated that the mechanical strength was lowered mainly by the grain orientation evolution or dynamic recrystallization occurring during early plastic deformation.Subsequently,thermal softening increased linearly and became the main softening mechanism.Noticeably,in the final stage,the thermal softening stress accounted for 78.4% of the total softening stress due to the sharp temperature increase,which inevitably leads to the stress collapse and potential failure of the alloy.展开更多
基金the National Key Research and Development Program of China(2016YFB0301102)the National Natural Science Foundation of China(Project No.51871036,51571045and 51421001)。
文摘Recent studies indicate that the texture distribution in friction stir welded(FSW)Mg alloys can be tailored and hence improve the joint performance.In this work,a crystal plasticity finite element modeling(CPFEM)was performed to understand the effects of texture distribution in stir zone(SZ)on the nonuniform plastic deformation and fracture localization.In total,six kinds of observed or purposely tilted texture distributions were modelled.The"concave-convex"appearance,as commonly observed in the tensile sample,was successfully simulated.It reveals that the mirror-symmetrical distribution of basal planes in the region of easy to activate basal slip(EABS)determined the"concave-convex"appearance in SZ-center.The asymmetrical appearance exchanged on plane A and plane B when the directions of basal planes were switched in the two EABS regions.Furthermore,the asymmetrical feature of plastic deformation was changed with varying the texture distribution in SZ.The"embossed"feature became more obvious in SZ-center first,and then gradually weakened with the c-axis rotated away from the weld plate plane.Severe necking was successfully simulated in SZ-center of FSW-H joint and in SZ-side of FSW-L joint.That might determine the observed fracture morphology.We believe that this simulation study is helpful for further improving the performance of FSW Mg joints.
基金financially supported by the National Natural Science Foundation of China(No.51571031)。
文摘A dynamic compression test was performed on α+β dual-phase titanium alloy Ti20C using a split Hopkinson pressure bar.The formation of adiabatic shear bands generated during the compression process was studied by combining the proposed multi-scale crystal plasticity finite element method with experimental measurements.The complex local micro region load was progressively extracted from the simulation results of a macro model and applied to an established three-dimensional multi-grain microstructure model.Subsequently,the evolution histories of the grain shape,size,and orientation inside the adiabatic shear band were quantitatively simulated.The results corresponded closely to the experimental results obtained via transmission electron microscopy and precession electron diffraction.Furthermore,by calculating the grain rotation and temperature rise inside the adiabatic shear band,the microstructural softening and thermal softening effects of typical heavily-deformed α grains were successfully decoupled.The results revealed that the microstructural softening stress was triggered and then stabilized(in general)at a relatively high value.This indicated that the mechanical strength was lowered mainly by the grain orientation evolution or dynamic recrystallization occurring during early plastic deformation.Subsequently,thermal softening increased linearly and became the main softening mechanism.Noticeably,in the final stage,the thermal softening stress accounted for 78.4% of the total softening stress due to the sharp temperature increase,which inevitably leads to the stress collapse and potential failure of the alloy.
