Extended finite element method （XFEM） implementation of the interaction integral methodology for evaluating the stress intensity factors （SIF） of the mixed-mode crack problem is presented. A discontinuous function...Extended finite element method （XFEM） implementation of the interaction integral methodology for evaluating the stress intensity factors （SIF） of the mixed-mode crack problem is presented. A discontinuous function and the near-tip asymptotic function are added to the classic finite element approximation to model the crack behavior. Two-state integral by the superposition of actual and auxiliary fields is derived to calculate the SIFs. Applications of the proposed technique to the inclined centre crack plate with inclined angle from 0° to 90° and slant edge crack plate with slant angle 45°, 67.5° and 90° are presented, and comparisons are made with closed form solutions. The results show that the proposed method is convenient, accurate and computationallv efficient.展开更多
The mechanical size effect of nanostructured,dual-phase CrCoNi medium-entropy alloy(MEA)was investigated by combining in-situ micro-compression testing with post-mortem electron microscopy analysis.The alloy possesses...The mechanical size effect of nanostructured,dual-phase CrCoNi medium-entropy alloy(MEA)was investigated by combining in-situ micro-compression testing with post-mortem electron microscopy analysis.The alloy possesses a superior yield strength up to~4 GPa,primarily due to its hierarchical microstructure including column nanograins,preferred orientation,a high density of planar defects and the presence of the hexagonal close packed(HCP)phase.While the yield strength of the alloy has shown sizeindependency,the deformation behaviour was strongly dependent on the sample size.Specifically,with decreasing the pillar diameters,the dominant deformation mode changed from highly localized and catastrophic shear banding to apparently homogeneous deformation with appreciable plasticity.This transition is believed to be governed by the sizedependent critical stress required for a shear band traversing the pillar and mediated by the competition between shearinduced softening and subsequent hardening mechanisms.In addition,an unexpected phase transformation from HCP to face-centered cubic(FCC)was observed in the highly localized deformation zones,leading to strain softening that contributed to accommodating plasticity.These findings provide insights into the criticality of sample dimensions in influencing mechanical behaviors of nanostructured metallic materials used for nanoelectromechanical systems.展开更多
In this work, a test method was developed to determine the interfacial fracture toughness of the air plasma sprayed （APS） thermal barrier coatings （TBCs） over a wide range of mode mixities. For this mixed-mode tes...In this work, a test method was developed to determine the interfacial fracture toughness of the air plasma sprayed （APS） thermal barrier coatings （TBCs） over a wide range of mode mixities. For this mixed-mode test method, the analytical expres- sions for the energy release rate and stress intensity factors were derived based on the energy theory and the concept of ＂equi- valence＂. The fidelity of these expressions was affirmed by selected finite element analysis. The experimental results showed that the critical energy release rate increased with the increase of the positive mode mixity, which was mainly due to the increase in contact/friction effect and plastic work dissipation with increasing shear mode loading. Furthermore, an elliptical interfacial failure criterion in terms of the stress intensity factors was proposed. The agreement between the experimental results in the literature and those in our work indicated that our test method and the corresponding analytical solutions can well determine the interfaeial fracture toughness of the TBCs over a wide range of mode mixities.展开更多
Transient effects of stress-strain fields in the vicinity of a stationary crack tip under high rate loads are discussed.Exact analytical solutions to near tip stresses are compared to fields prescribed by leading term...Transient effects of stress-strain fields in the vicinity of a stationary crack tip under high rate loads are discussed.Exact analytical solutions to near tip stresses are compared to fields prescribed by leading terms(one or several) of Williams asymptotic expansion.Influence of load application mode,time(or,which is the same,distance from a crack tip) and Poisson's ratio on this discrepancy is extensively examined.Some effects connected with crack tip propagation speed are also discussed.Significant inconsistencies between real(or received in numerical solutions of state equations-e.g.finite element computations) crack tip fields and stress intensity factor(SIF) singular field observed by numerous researchers are explained.The scope of problems where SIF field can be used for correct prediction of dynamic stress-strain fields in the crack tip region is established.Possibility to correctly approximate fields that are not SIF dominated,accounting additional terms of Williams expansion,is studied.展开更多
基金Projects(41172244,41072224) supported by the National Natural Science Foundation of ChinaProject(2009GGJS-037) supported by the Foundation of Youths Key Teacher by the Henan Educational Committee,China
文摘Extended finite element method （XFEM） implementation of the interaction integral methodology for evaluating the stress intensity factors （SIF） of the mixed-mode crack problem is presented. A discontinuous function and the near-tip asymptotic function are added to the classic finite element approximation to model the crack behavior. Two-state integral by the superposition of actual and auxiliary fields is derived to calculate the SIFs. Applications of the proposed technique to the inclined centre crack plate with inclined angle from 0° to 90° and slant edge crack plate with slant angle 45°, 67.5° and 90° are presented, and comparisons are made with closed form solutions. The results show that the proposed method is convenient, accurate and computationallv efficient.
基金supported by the Australian Research Council Discovery Projects Grantpartly supported by the Fundamental Research Funds for the Central Universities(SWU118105)+1 种基金the financial support from Australia Research Council(DE170100053)the Robinson Fellowship Scheme of the University of Sydney(G200726)。
文摘The mechanical size effect of nanostructured,dual-phase CrCoNi medium-entropy alloy(MEA)was investigated by combining in-situ micro-compression testing with post-mortem electron microscopy analysis.The alloy possesses a superior yield strength up to~4 GPa,primarily due to its hierarchical microstructure including column nanograins,preferred orientation,a high density of planar defects and the presence of the hexagonal close packed(HCP)phase.While the yield strength of the alloy has shown sizeindependency,the deformation behaviour was strongly dependent on the sample size.Specifically,with decreasing the pillar diameters,the dominant deformation mode changed from highly localized and catastrophic shear banding to apparently homogeneous deformation with appreciable plasticity.This transition is believed to be governed by the sizedependent critical stress required for a shear band traversing the pillar and mediated by the competition between shearinduced softening and subsequent hardening mechanisms.In addition,an unexpected phase transformation from HCP to face-centered cubic(FCC)was observed in the highly localized deformation zones,leading to strain softening that contributed to accommodating plasticity.These findings provide insights into the criticality of sample dimensions in influencing mechanical behaviors of nanostructured metallic materials used for nanoelectromechanical systems.
基金supports from the National Natural Science Foundation of China(No. 10872105 and No. 51071094)
文摘In this work, a test method was developed to determine the interfacial fracture toughness of the air plasma sprayed （APS） thermal barrier coatings （TBCs） over a wide range of mode mixities. For this mixed-mode test method, the analytical expres- sions for the energy release rate and stress intensity factors were derived based on the energy theory and the concept of ＂equi- valence＂. The fidelity of these expressions was affirmed by selected finite element analysis. The experimental results showed that the critical energy release rate increased with the increase of the positive mode mixity, which was mainly due to the increase in contact/friction effect and plastic work dissipation with increasing shear mode loading. Furthermore, an elliptical interfacial failure criterion in terms of the stress intensity factors was proposed. The agreement between the experimental results in the literature and those in our work indicated that our test method and the corresponding analytical solutions can well determine the interfaeial fracture toughness of the TBCs over a wide range of mode mixities.
基金supported by RFBR research grants, Russian Federal programs and academic programs of the Russian Academy of Sciences
文摘Transient effects of stress-strain fields in the vicinity of a stationary crack tip under high rate loads are discussed.Exact analytical solutions to near tip stresses are compared to fields prescribed by leading terms(one or several) of Williams asymptotic expansion.Influence of load application mode,time(or,which is the same,distance from a crack tip) and Poisson's ratio on this discrepancy is extensively examined.Some effects connected with crack tip propagation speed are also discussed.Significant inconsistencies between real(or received in numerical solutions of state equations-e.g.finite element computations) crack tip fields and stress intensity factor(SIF) singular field observed by numerous researchers are explained.The scope of problems where SIF field can be used for correct prediction of dynamic stress-strain fields in the crack tip region is established.Possibility to correctly approximate fields that are not SIF dominated,accounting additional terms of Williams expansion,is studied.
