Due to the nonlinearity of breathing crack, cracked structure under excitation of a single frequency always generates higher harmonic components. In this paper, operational deflection shape (ODS) at excitation frequen...Due to the nonlinearity of breathing crack, cracked structure under excitation of a single frequency always generates higher harmonic components. In this paper, operational deflection shape (ODS) at excitation frequency and its higher harmonic components are used to map the deflection pattern of cracked structure. While ODS is sensitive to local variation of structure in nature, a new concept named transmissibility of operational deflection shape (TODS) has been defined for crack localization using beam-like structure. The transmissibility indicates the energy transfer from basic frequency to higher frequency. Then, Teager energy operator (TEO) is employed as a singularity detector to reveal and characterize the features of TODS. Numerical and experimental analysis in cantilever beam show that TODS has strong sensitivity to crack and can locate the crack correctly.展开更多
Interfaces play a crucial role in influencing the mechanical properties of Mg alloys.For Mg-Li dual-phase alloy,the type of interfaces is complex,which includes both grain boundary and phase boundary,and the influence...Interfaces play a crucial role in influencing the mechanical properties of Mg alloys.For Mg-Li dual-phase alloy,the type of interfaces is complex,which includes both grain boundary and phase boundary,and the influence of such interfaces on the damage nucleation is yet to be explored.In this paper,in-situ scanning electron microscopy(SEM)based measurements were carried out to investigate the meso-scale damage nucleation mechanisms of the Mg-6Li dual-phase alloy.Results show that 94.8%of cracks are nucleated at the α-Mg grain boundary in the post-uniform elongation stage,while 5.2%are at phase boundary and almost no crack at the β-Li grain boundary.The initiation of α-Mg grain boundary cracks is attributed to strain incompatibility,which induces micro-strain localization,and then causes grain boundary sliding(GBS)and crack nucleation.Deformation compatibility analysis reveals that the geometric compatibility factor(Mk)can be used to predict the nucleation of α-Mg grain boundary crack.When Mk is lower than 0.075,α-Mg grain boundary cracks tend to form.Few cracks are generated at the phase boundary is due to the mild strain partitioning between α-Mg phase and β-Li phase and may also be partly attributed to multiple slip systems in body-centered cubic(BCC)-structured β-Li phase,which can accommodate well with the deformation of adjacent α-Mg phase.展开更多
The interface wave traveling along the bound- ary of two materials has been studied for nearly a century. However, experiments, engineering applications, and interface wave applications to the non-destructive inspec- ...The interface wave traveling along the bound- ary of two materials has been studied for nearly a century. However, experiments, engineering applications, and interface wave applications to the non-destructive inspec- tion of interlaminar composite have developed slowly. In this research, an experiment that applies Stoneley waves （a type of interfacial wave between two solid half-spaces） is implemented to detect the damage in a multilayer structure. The feasibility of this method is also verified. First, the wave velocity and wave structure of Stoneley waves at a perfectly bonded aluminum-steel interface are obtained by solving the Stoneley wave dispersion equation of two elastic half-spaces. Thereafter, an experiment is conducted to measure the Stoneley wave velocity of an aluminum- steel laminated beam and to locate interlaminar cracks by referring to the Stoneley wave velocity and echo wave time. Results indicate that the location error is less than 2%. Therefore, Stoneley waves show great potential as a non-destructive inspection method of a multilayer structure.展开更多
Flow localization, which is an importantmode of deformation in engineering materi-als, has been the interesting subject ofa number of experimental observationsand theoretical investigations in recentyears. However, t... Flow localization, which is an importantmode of deformation in engineering materi-als, has been the interesting subject ofa number of experimental observationsand theoretical investigations in recentyears. However, the basic mechanism ofthe phenomena is not well understood atpresent. In a tensile test, the initiationand growth of a shear band are often simul-taneous. Therefore, it is rather difficult展开更多
Crystallographic plasticity was applied to study the initiation of micro cracks on the smooth surface of polycrystalline under uniform applied stress. Even under the uniform external stress, due to the different cryst...Crystallographic plasticity was applied to study the initiation of micro cracks on the smooth surface of polycrystalline under uniform applied stress. Even under the uniform external stress, due to the different crystallographic orientations of the grains in the polycrystalline, there is un-uniform stress distribution and the deformation is also not uniform. Under the fatigue loading, the roughness increases with the number of fatigue, and deformation will localize in some places, where micro cracks form.展开更多
文摘Due to the nonlinearity of breathing crack, cracked structure under excitation of a single frequency always generates higher harmonic components. In this paper, operational deflection shape (ODS) at excitation frequency and its higher harmonic components are used to map the deflection pattern of cracked structure. While ODS is sensitive to local variation of structure in nature, a new concept named transmissibility of operational deflection shape (TODS) has been defined for crack localization using beam-like structure. The transmissibility indicates the energy transfer from basic frequency to higher frequency. Then, Teager energy operator (TEO) is employed as a singularity detector to reveal and characterize the features of TODS. Numerical and experimental analysis in cantilever beam show that TODS has strong sensitivity to crack and can locate the crack correctly.
基金National Natural Science Foundation of China(Nos.52005412,52305506 and U2241231)Fundamental Research Funds for the Central Universities(No.D5000230081).
文摘Interfaces play a crucial role in influencing the mechanical properties of Mg alloys.For Mg-Li dual-phase alloy,the type of interfaces is complex,which includes both grain boundary and phase boundary,and the influence of such interfaces on the damage nucleation is yet to be explored.In this paper,in-situ scanning electron microscopy(SEM)based measurements were carried out to investigate the meso-scale damage nucleation mechanisms of the Mg-6Li dual-phase alloy.Results show that 94.8%of cracks are nucleated at the α-Mg grain boundary in the post-uniform elongation stage,while 5.2%are at phase boundary and almost no crack at the β-Li grain boundary.The initiation of α-Mg grain boundary cracks is attributed to strain incompatibility,which induces micro-strain localization,and then causes grain boundary sliding(GBS)and crack nucleation.Deformation compatibility analysis reveals that the geometric compatibility factor(Mk)can be used to predict the nucleation of α-Mg grain boundary crack.When Mk is lower than 0.075,α-Mg grain boundary cracks tend to form.Few cracks are generated at the phase boundary is due to the mild strain partitioning between α-Mg phase and β-Li phase and may also be partly attributed to multiple slip systems in body-centered cubic(BCC)-structured β-Li phase,which can accommodate well with the deformation of adjacent α-Mg phase.
基金This work was supported by the National Natural Science Foundation of China （Grant No. 51475356）.
文摘The interface wave traveling along the bound- ary of two materials has been studied for nearly a century. However, experiments, engineering applications, and interface wave applications to the non-destructive inspec- tion of interlaminar composite have developed slowly. In this research, an experiment that applies Stoneley waves （a type of interfacial wave between two solid half-spaces） is implemented to detect the damage in a multilayer structure. The feasibility of this method is also verified. First, the wave velocity and wave structure of Stoneley waves at a perfectly bonded aluminum-steel interface are obtained by solving the Stoneley wave dispersion equation of two elastic half-spaces. Thereafter, an experiment is conducted to measure the Stoneley wave velocity of an aluminum- steel laminated beam and to locate interlaminar cracks by referring to the Stoneley wave velocity and echo wave time. Results indicate that the location error is less than 2%. Therefore, Stoneley waves show great potential as a non-destructive inspection method of a multilayer structure.
文摘 Flow localization, which is an importantmode of deformation in engineering materi-als, has been the interesting subject ofa number of experimental observationsand theoretical investigations in recentyears. However, the basic mechanism ofthe phenomena is not well understood atpresent. In a tensile test, the initiationand growth of a shear band are often simul-taneous. Therefore, it is rather difficult
文摘Crystallographic plasticity was applied to study the initiation of micro cracks on the smooth surface of polycrystalline under uniform applied stress. Even under the uniform external stress, due to the different crystallographic orientations of the grains in the polycrystalline, there is un-uniform stress distribution and the deformation is also not uniform. Under the fatigue loading, the roughness increases with the number of fatigue, and deformation will localize in some places, where micro cracks form.
