A crystal plasticity finite element(CPFE)model was established and 2D simulations were carried out to study the relationship between microvoids and the microplasticity deformation behavior of the dual-phase titanium a...A crystal plasticity finite element(CPFE)model was established and 2D simulations were carried out to study the relationship between microvoids and the microplasticity deformation behavior of the dual-phase titanium alloy under high cyclic loading.Results show that geometrically necessary dislocations(GND)tend to accumulate around the microvoids,leading to an increment of average GND density.The influence of curvature in the tip plastic zone(TPZ)on GND density is greater than that of the size of the microvoid.As the curvature in TPZ and the size of the microvoid increase,the cumulative shear strain(CSS)in the primaryα,secondaryα,andβphases increases.Shear deformation in the prismatic slip system is dominant in the primaryαphase.As the distance between the microvoids increases,the interactive influence of the microvoids on the cumulative shear strain decreases.展开更多
Based on the bulk free energy density and the degenerate mobility constructed by the quartic double-well potential function,a phase field model is established to simulate the evolution of intragranular microvoids due ...Based on the bulk free energy density and the degenerate mobility constructed by the quartic double-well potential function,a phase field model is established to simulate the evolution of intragranular microvoids due to surface diffusion in a stress field.The corresponding phase field governing equations are derived.The evolution of elliptical microvoids with different stressesΛ,aspect ratiosβand linewidths hˉis calculated using the mesh adaptation finite element method and the reliability of the procedure is verified.The results show that there exist critical values of the stressΛc,the aspect ratioβc and the linewidth hˉc of intragranular microvoids under equivalent biaxial tensile stress.When Λ≥Λ_(c),β≥β_(c) or h≤h_(c),the elliptical microvoids are instable with an extending crack tip.WhenΛ<Λ_(c),β<β_(c) or hˉ>h_(c),the elliptical microvoids gradually cylindricalize and remain a stable shape.The instability time decreases with increasing the stress or the aspect ratio,while increases with increasing the linewidth.In addition,for the interconnects containing two elliptical voids not far apart,the stress will promote the merging of the voids.展开更多
The combined effects of void size and void shape on the void growth are studied by using the classical spectrum method. An infinite solid containing an isolated prolate spheroidal void is considered to depict the void...The combined effects of void size and void shape on the void growth are studied by using the classical spectrum method. An infinite solid containing an isolated prolate spheroidal void is considered to depict the void shape effect and the Fleck-Hutchinson phenomenological strain gradient plasticity theory is employed to capture the size effects. It is found that the combined effects of void size and void shape are mainly controlled by the remote stress triaxiality. Based on this, a new size-dependent void growth model similar to the Rice-Tracey model is proposed and an important conclusion about the size-dependent void growth is drawn： the growth rate of the void with radius smaller than a critical radius rc may be ignored. It is interesting that rc. is a material constant independent of the initial void shape and the remote stress triaxiality.展开更多
In this paper,morphological structure,thermodynamic compatibility and relationship be-tween porosities and blend ratios of the wet coagulated PU/PVA sheets were studied by meansof observation of scanning electronic mi...In this paper,morphological structure,thermodynamic compatibility and relationship be-tween porosities and blend ratios of the wet coagulated PU/PVA sheets were studied by meansof observation of scanning electronic micrographies,tests of dynamic mechanical properties,moisture regain and vapor permeability.Furthermore,the formation of microvoids at interfacesof separated phases was discussed and a microvoid formation mechanism at phase interfaces ofhydrophobic-hydrophilic blends was suggested and compared with that ofhydrophobic-hydrophobic blends.展开更多
The statistical evolution of microvoids under high stress triaxiality is investigated. Based on the expression for the void growth rate in a power-law viscous matrix and the balance law of microvoids’ number, the evo...The statistical evolution of microvoids under high stress triaxiality is investigated. Based on the expression for the void growth rate in a power-law viscous matrix and the balance law of microvoids’ number, the evolution of microvoids’ number density under dynamic loading is studied. Thus, the si2E distribution functions of microvoids are found from the theoretical analysis, and the effect of strain rate-sensitivity of the matrix on the evolution of microvoids is examined. The present theoretical analysis may provide a reasonable explanation for the experimental phenomena observed by previous researchers.展开更多
Spallation, rupture under impulsive tensile loading, is a dynamic failure process involving the collective evolution and accumulation of enormous microdamage in solids. In contrast to traditional alloys, the spallatio...Spallation, rupture under impulsive tensile loading, is a dynamic failure process involving the collective evolution and accumulation of enormous microdamage in solids. In contrast to traditional alloys, the spallation mechanism in medium entropy alloys, the recently emerged multiprinciple and chemically disordered alloys, is poorly understood. Here we conduct molecular dynamics simulations and first principle calculations to investigate the effects of impact velocities and the local chemical order on spallation microvoid nucleation in a CrCoNi medium entropy alloy under shock wave loading. As the impact velocity increases, the microvoid nucleation site exhibits a transition from the grain boundaries to the grains to release redundant imposed energy. During the intragranular nucleation process, microvoids nucleate in the poor-Cr region with a large local nonaffine deformation, which is attributed to the weak metallic bonds in this position with sparse free electrons. For intergranular nucleation, a Franke-like dislocation source forms through the dislocation reaction, leading to enormous dislocations piling up in a narrow twin stripe, which markedly increases the local stored energy and promotes microvoid nucleation. These results shed light on the mechanism of spallation in chemically complexed medium entropy alloys.展开更多
基金the National Key Research and Development Program of China(No.2021YFB3702603).
文摘A crystal plasticity finite element(CPFE)model was established and 2D simulations were carried out to study the relationship between microvoids and the microplasticity deformation behavior of the dual-phase titanium alloy under high cyclic loading.Results show that geometrically necessary dislocations(GND)tend to accumulate around the microvoids,leading to an increment of average GND density.The influence of curvature in the tip plastic zone(TPZ)on GND density is greater than that of the size of the microvoid.As the curvature in TPZ and the size of the microvoid increase,the cumulative shear strain(CSS)in the primaryα,secondaryα,andβphases increases.Shear deformation in the prismatic slip system is dominant in the primaryαphase.As the distance between the microvoids increases,the interactive influence of the microvoids on the cumulative shear strain decreases.
基金supported by the Natural Science Foundation of Jiangsu Province of China (No. BK20141407)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘Based on the bulk free energy density and the degenerate mobility constructed by the quartic double-well potential function,a phase field model is established to simulate the evolution of intragranular microvoids due to surface diffusion in a stress field.The corresponding phase field governing equations are derived.The evolution of elliptical microvoids with different stressesΛ,aspect ratiosβand linewidths hˉis calculated using the mesh adaptation finite element method and the reliability of the procedure is verified.The results show that there exist critical values of the stressΛc,the aspect ratioβc and the linewidth hˉc of intragranular microvoids under equivalent biaxial tensile stress.When Λ≥Λ_(c),β≥β_(c) or h≤h_(c),the elliptical microvoids are instable with an extending crack tip.WhenΛ<Λ_(c),β<β_(c) or hˉ>h_(c),the elliptical microvoids gradually cylindricalize and remain a stable shape.The instability time decreases with increasing the stress or the aspect ratio,while increases with increasing the linewidth.In addition,for the interconnects containing two elliptical voids not far apart,the stress will promote the merging of the voids.
基金The project supported by the National Natural Science Foundation of China(A10102006)the New Century Excellent Talents in Universities of China.
文摘The combined effects of void size and void shape on the void growth are studied by using the classical spectrum method. An infinite solid containing an isolated prolate spheroidal void is considered to depict the void shape effect and the Fleck-Hutchinson phenomenological strain gradient plasticity theory is employed to capture the size effects. It is found that the combined effects of void size and void shape are mainly controlled by the remote stress triaxiality. Based on this, a new size-dependent void growth model similar to the Rice-Tracey model is proposed and an important conclusion about the size-dependent void growth is drawn： the growth rate of the void with radius smaller than a critical radius rc may be ignored. It is interesting that rc. is a material constant independent of the initial void shape and the remote stress triaxiality.
文摘In this paper,morphological structure,thermodynamic compatibility and relationship be-tween porosities and blend ratios of the wet coagulated PU/PVA sheets were studied by meansof observation of scanning electronic micrographies,tests of dynamic mechanical properties,moisture regain and vapor permeability.Furthermore,the formation of microvoids at interfacesof separated phases was discussed and a microvoid formation mechanism at phase interfaces ofhydrophobic-hydrophilic blends was suggested and compared with that ofhydrophobic-hydrophobic blends.
基金Laboratory for Nonlinear Mechanics of Continuous Media(Institute of Mechanics,Chinese Academy of Sciences)Doctoral Program Foundation of the State Education Commission of China.
文摘The statistical evolution of microvoids under high stress triaxiality is investigated. Based on the expression for the void growth rate in a power-law viscous matrix and the balance law of microvoids’ number, the evolution of microvoids’ number density under dynamic loading is studied. Thus, the si2E distribution functions of microvoids are found from the theoretical analysis, and the effect of strain rate-sensitivity of the matrix on the evolution of microvoids is examined. The present theoretical analysis may provide a reasonable explanation for the experimental phenomena observed by previous researchers.
基金supported by the National Key Research and Development Program of China (Grant No. 2017YFB0702003)the National Natural Science Foundation of China (NSFC) (Grant Nos. 11790292, 11972346 and 11672316)+3 种基金the NSFC Basic Science Center Program for “Multiscale Problems in Nonlinear Mechanics” (Grant No. 11988102)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDB22040302 and XDB22040303)the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (Grant No. QYZDJSSWJSC011)the Science Challenge Project (Grant No. TZ2018001)。
文摘Spallation, rupture under impulsive tensile loading, is a dynamic failure process involving the collective evolution and accumulation of enormous microdamage in solids. In contrast to traditional alloys, the spallation mechanism in medium entropy alloys, the recently emerged multiprinciple and chemically disordered alloys, is poorly understood. Here we conduct molecular dynamics simulations and first principle calculations to investigate the effects of impact velocities and the local chemical order on spallation microvoid nucleation in a CrCoNi medium entropy alloy under shock wave loading. As the impact velocity increases, the microvoid nucleation site exhibits a transition from the grain boundaries to the grains to release redundant imposed energy. During the intragranular nucleation process, microvoids nucleate in the poor-Cr region with a large local nonaffine deformation, which is attributed to the weak metallic bonds in this position with sparse free electrons. For intergranular nucleation, a Franke-like dislocation source forms through the dislocation reaction, leading to enormous dislocations piling up in a narrow twin stripe, which markedly increases the local stored energy and promotes microvoid nucleation. These results shed light on the mechanism of spallation in chemically complexed medium entropy alloys.
