Compositionally undulating step-graded Al（Ga）InxAs （x = 0.05-0.52） buffers with the following InP layer were grown by metal-organic chemical vapor deposition （MOCVD） on （001） GaAs with a 15° miscut. The d...Compositionally undulating step-graded Al（Ga）InxAs （x = 0.05-0.52） buffers with the following InP layer were grown by metal-organic chemical vapor deposition （MOCVD） on （001） GaAs with a 15° miscut. The dislocation dis- tribution and tilts of the epilayers were examined using x-ray rocking curve and （004） reciprocal space maps （RSM） along two orthogonal （110） directions. The results suggested that such reverse-graded layers have different effects on a and 13 dislocations. A higher dislocation density was observed along the [ 110] direction and an epilayer tilt of - 1.43° was attained in the [1-10] direction when a reverse-graded layer strategy was employed. However, for conventional step-graded samples, the dislocation density is normally higher along the [1-10] direction.展开更多
Dislocation distribution functions of the edges of mode Ⅲ propagation crack subjected to three types of loads were studied by the methods of the theory of complex variable functions,by which,the problems researched w...Dislocation distribution functions of the edges of mode Ⅲ propagation crack subjected to three types of loads were studied by the methods of the theory of complex variable functions,by which,the problems researched were facilely transformed into Riemann-Hilbert problems and Keldysh-Sedov mixed boundary value problems. Analytical solutions of stresses,displacement and dynamic stress intensity factor were obtained by the measures of the theory of self-similar functions and corresponding differential and integral operation. In terms of the relationship between dislocation distribution functions and displacements,analytical solutions of dislocation distribution functions were obttained,and variational rules of dislocation distribution functions were depicted.展开更多
In this paper,the mutual influence of plastic behaviors between kinked macro-crack and kinked micro-crack is analyzed based on the distributed dislocation technique and the dislocation-free zone model.A novel theoreti...In this paper,the mutual influence of plastic behaviors between kinked macro-crack and kinked micro-crack is analyzed based on the distributed dislocation technique and the dislocation-free zone model.A novel theoretical model for the size of the plastic zone is proposed,where the length of the dislocation array calculated in a specific direction is utilized to characterize the size of the plastic zone at the crack tip.The results demonstrate that,compared with the length of the dislocation array distributed along the crack direction,the length of the dislocation array distributed at a certain specific angle can more accurately characterize the plastic zone at the crack tip.When compared with the results of finite element analysis,the relative error is within 0.2%.Within the theoretical framework of this paper,it is considered that when the dislocation array is set at the crack tip and forms an angle of approximately 25°with respect to the horizontal direction,the calculated length of the dislocation array can effectively characterize the size of the plastic zone.The dislocation density increases with the decrease of the kinking angle of the crack.These results are conducive to predicting the plastic and fracture behaviors of materials containing kinked cracks.展开更多
This paper presents a numerical solution to model multiple cracks in a finite plate of an elastic isotropic material. Both the boundaries and the cracks are modeled by distributed dislocations. This method results in ...This paper presents a numerical solution to model multiple cracks in a finite plate of an elastic isotropic material. Both the boundaries and the cracks are modeled by distributed dislocations. This method results in a system of singular integral equations with Cauchy kernels which can be solved by Gauss-Chebyshev quadrature method. Four examples are provided to assess the capability of this method.展开更多
The fracture behavior of superconducting tapes with central and edge oblique cracks subject to electromagnetic forces is investigated. Maxwell's equations and the critical state-Bean model are used to analytically...The fracture behavior of superconducting tapes with central and edge oblique cracks subject to electromagnetic forces is investigated. Maxwell's equations and the critical state-Bean model are used to analytically determine the magnetic flux density and electromagnetic force distributions in superconducting tapes containing central and edge oblique cracks. The distributed dislocation technique(DDT) transforms the mixed boundary value problem into a Cauchy singular integral equation, which is then solved by the Gauss-Chebyshev quadrature method to determine the stress intensity factors(SIFs).The model's accuracy is validated by comparing the calculated electromagnetic force distribution for the edge oblique crack and the SIFs for both crack types with the existing results. The findings indicate that the current and electromagnetic forces are significantly affected by the crack length and oblique angle. Specifically, for central oblique cracks, a smaller oblique angle enhances the risk of crack propagation, and a higher initial magnetization intensity poses greater danger under field cooling(FC) excitation. In contrast, for edge oblique cracks, a larger angle increases the likelihood of tape fractures. This study provides important insights into the fracture behavior and mechanical failure mechanisms of superconducting tapes with oblique cracks.展开更多
Combining the continuously distributed dislocation technique(DDT)and the von Mises yield criterion,new double-crack and multi-crack models were established.The influences of multi-segment kinked micro-cracks and group...Combining the continuously distributed dislocation technique(DDT)and the von Mises yield criterion,new double-crack and multi-crack models were established.The influences of multi-segment kinked micro-cracks and groups of kinked micro-cracks on the plastic behavior of the macro-crack were investigated.The results show that a smaller kinking angle of the micro-crack enhances its influence on the plastic deformation of the macro-crack,potentially leading to plastic zone fusion.Meanwhile,micro-cracks with smaller kinking angles exert a stronger attracting force on macro-crack growth,facilitating convergence between them.Furthermore,annularly distributed micro-crack groups demonstrate a more pronounced attraction on macro-crack propagation compared to linearly distributed micro-crack groups.The double-crack and multi-crack models established in this paper offer a theoretical framework for analyzing the plastic fracture behavior of metallic materials containing complex kinked cracks.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.61376065)
文摘Compositionally undulating step-graded Al（Ga）InxAs （x = 0.05-0.52） buffers with the following InP layer were grown by metal-organic chemical vapor deposition （MOCVD） on （001） GaAs with a 15° miscut. The dislocation dis- tribution and tilts of the epilayers were examined using x-ray rocking curve and （004） reciprocal space maps （RSM） along two orthogonal （110） directions. The results suggested that such reverse-graded layers have different effects on a and 13 dislocations. A higher dislocation density was observed along the [ 110] direction and an epilayer tilt of - 1.43° was attained in the [1-10] direction when a reverse-graded layer strategy was employed. However, for conventional step-graded samples, the dislocation density is normally higher along the [1-10] direction.
基金Sponsored by the Postdoctoral Science Fundation of China (Grant No. 200303337 )the National Natural Science Foundation of China (Grant No.30205035)
文摘Dislocation distribution functions of the edges of mode Ⅲ propagation crack subjected to three types of loads were studied by the methods of the theory of complex variable functions,by which,the problems researched were facilely transformed into Riemann-Hilbert problems and Keldysh-Sedov mixed boundary value problems. Analytical solutions of stresses,displacement and dynamic stress intensity factor were obtained by the measures of the theory of self-similar functions and corresponding differential and integral operation. In terms of the relationship between dislocation distribution functions and displacements,analytical solutions of dislocation distribution functions were obttained,and variational rules of dislocation distribution functions were depicted.
基金supported by the National Natural Science Foundation of China(Grant No.12393782).
文摘In this paper,the mutual influence of plastic behaviors between kinked macro-crack and kinked micro-crack is analyzed based on the distributed dislocation technique and the dislocation-free zone model.A novel theoretical model for the size of the plastic zone is proposed,where the length of the dislocation array calculated in a specific direction is utilized to characterize the size of the plastic zone at the crack tip.The results demonstrate that,compared with the length of the dislocation array distributed along the crack direction,the length of the dislocation array distributed at a certain specific angle can more accurately characterize the plastic zone at the crack tip.When compared with the results of finite element analysis,the relative error is within 0.2%.Within the theoretical framework of this paper,it is considered that when the dislocation array is set at the crack tip and forms an angle of approximately 25°with respect to the horizontal direction,the calculated length of the dislocation array can effectively characterize the size of the plastic zone.The dislocation density increases with the decrease of the kinking angle of the crack.These results are conducive to predicting the plastic and fracture behaviors of materials containing kinked cracks.
基金supported by National Natural Science Foundation of China(No.51174162)
文摘This paper presents a numerical solution to model multiple cracks in a finite plate of an elastic isotropic material. Both the boundaries and the cracks are modeled by distributed dislocations. This method results in a system of singular integral equations with Cauchy kernels which can be solved by Gauss-Chebyshev quadrature method. Four examples are provided to assess the capability of this method.
基金Project supported by the National Natural Science Foundation of China (Nos. 12232005 and 12072101)the Ningxia Natural Science Foundation of China (No. 2024AAC04004)。
文摘The fracture behavior of superconducting tapes with central and edge oblique cracks subject to electromagnetic forces is investigated. Maxwell's equations and the critical state-Bean model are used to analytically determine the magnetic flux density and electromagnetic force distributions in superconducting tapes containing central and edge oblique cracks. The distributed dislocation technique(DDT) transforms the mixed boundary value problem into a Cauchy singular integral equation, which is then solved by the Gauss-Chebyshev quadrature method to determine the stress intensity factors(SIFs).The model's accuracy is validated by comparing the calculated electromagnetic force distribution for the edge oblique crack and the SIFs for both crack types with the existing results. The findings indicate that the current and electromagnetic forces are significantly affected by the crack length and oblique angle. Specifically, for central oblique cracks, a smaller oblique angle enhances the risk of crack propagation, and a higher initial magnetization intensity poses greater danger under field cooling(FC) excitation. In contrast, for edge oblique cracks, a larger angle increases the likelihood of tape fractures. This study provides important insights into the fracture behavior and mechanical failure mechanisms of superconducting tapes with oblique cracks.
基金supported by the National Natural Science Foundation of China(Grant No.12393782).
文摘Combining the continuously distributed dislocation technique(DDT)and the von Mises yield criterion,new double-crack and multi-crack models were established.The influences of multi-segment kinked micro-cracks and groups of kinked micro-cracks on the plastic behavior of the macro-crack were investigated.The results show that a smaller kinking angle of the micro-crack enhances its influence on the plastic deformation of the macro-crack,potentially leading to plastic zone fusion.Meanwhile,micro-cracks with smaller kinking angles exert a stronger attracting force on macro-crack growth,facilitating convergence between them.Furthermore,annularly distributed micro-crack groups demonstrate a more pronounced attraction on macro-crack propagation compared to linearly distributed micro-crack groups.The double-crack and multi-crack models established in this paper offer a theoretical framework for analyzing the plastic fracture behavior of metallic materials containing complex kinked cracks.
