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In this paper, the L-integral analysis for two nano-sized voids in plane elasticity under uniaxial loading is present. Three surface parameters are considered including the surface tension and two surface Lamé constants. Attention is focused on the mutual influence on the L-integral from both the surface effect at voids' rims and the interacting effect between voids. A close-form expression of L-integral for multiple nano voids is obtained. Comparing with those in macro fracture mechanics, the L-integral shows some different features when the surface effect is taken into account. It is concluded that under tensile loading and due to the mutual influence, the L-integral might be either positive or negative, depending on the loading level. The numerical results show that the surface tension is the dominant one in surface parameters on impacting the L-integral. It is also concluded that the surface effect shields the energy release (positive L-integral value) while enhances the energy absorption (negative L-integral value). The two-state L-integral analysis is performed to clarify the way that the surface effect impacts the L-integral. It is concluded that the contribution to L-integral from the voids' configuration could either be negative or positive, while that from the surface effect is always negative. Besides, the size dependence in the present problem is studied in detail. [ABSTRACT FROM AUTHOR]

This paper provides an explanation for the authors' recent conclusions as why the M-integral could be negative for a nano-void (hole) in elastic materials under tensile, bi-axes tensile, and bi-axes tensile-compress loadings (Hui T, Chen YH, in ASME J Appl Mech 77:021019-1-9, ; 024505-1-5, ). Attention is focused on whether the area of the nano-void under each of four different kinds of loading is contractive when compared to the original geometrical area without loading. The four kinds of loading are as follows: (1) simple tensile loading; (2) bi-axes tensile loading; (3) bi-axes tensile-compression loading; and (4) purely shear loading. It is concluded that, unlike those for a macro/micro hole, the area of the nano-void under relatively lower amplitude of the loadings (1) and (2) is always smaller than the original area of the same void before loading. This reduction in the nano-void area is induced from the surface effect including the surface tension and the surface Lamé constants along the nano-void rim. Thus, these two kinds of loading can either decrease or increase the nano-void area depending on the amplitude of the loading. Under a relatively lower tensile loading, the area contraction occurs but not always corresponding to the negative value of the M-integral, whereas under a relatively higher tensile loading, the area expansion occurs but not always corresponding to the positive value of the M-integral. This again verifies that the positive value of the M-integral does not always correspond to the energy release due to the nano-hole expansion, rather, the area contraction might yield the energy release either. Under bi-axes tensile compression or purely shear loading, this feature disappears. [ABSTRACT FROM AUTHOR]

By considering an isotropic elastic dielectric material as a transversely isotropic piezoelectric material with little piezoelectricity, the interface crack problem in elastic/piezoelectric bimaterials is treated in this paper based on Stroh's complex potential theory (1958) with the impermeable crack model. In order to obtain universal results, Numerical results of the near tip stress field and the electric field for 35 kinds of dissimilar bimaterials constructed by five kinds of elastic dielectric materials, namely Epoxy, Polymer, Al2O3, SiC and Si3N4, and seven kinds of piezoelectric ceramics, namely PZT-4, BaTiO3, PZT-5H, PZT-6B, PZT-7A, P-7, and PZT-PIC151, are presented. It is concluded that all the combinations lead to the same results: in which the first crack tip singularity parameter e does not vanish whereas the second parameter ? always vanishes. From the physical point of view, an interface crack in such a dissimilar material shows a similar oscillating singularity as that in dissimilar elastic bimaterials. Moreover, by using a maximization value technique, the regular inverse square root singularityr-1/2 of the stress and the electric field at the crack tip can be realized, although, theoretically, an interface crack in such bimaterials possesses the well-known oscillating singularityr-1/2± ie. Of great significance is that, in the absence of mechanical loadings, a purely electric loading can induce relative large model I or II stress intensity factor for a interface crack in some elastic/piezoelectric bimaterials, which implies that the electric-induced failure may be realized in such bimaterials. [ABSTRACT FROM AUTHOR]