Papers by Author: Bao Lin Wang

Abstract: In this paper, we analyze the influence of surface effects including residual surface stress, surface piezoelectric and surface elasticity on the buckling behavior of piezoelectric nanobeams by using the Timoshenko beam theory and surface piezoelectricity model. The critical electric potential for buckling of piezoelectric nanobeams with different boundary condition is obtained analytically. From the results, it is found that the surface piezoelectric reduces the critical electric potential. However, a positive residual surface stress increases the critical electric potential. In addition, the shear deformation reduces the critical electric potential, and the influence of shear deformation become more significant for a stubby piezoelectric nanobeam.

Abstract: SiC whisker-reinforced ZrB2 matrix ultra-high temperature ceramic were prepared at 2000°C for 1 h under 30MPa by hot pressing and the effects of whisker on flexural strength and fracture toughness of the composites was examined. The flexural strength and fracture toughness are 510±25MPa and 4.05±0.20MPa⋅m1/2 at room temperature, respectively. Comparing with the SiC particles-reinforced ZrB2 ceramic, no significant increase in both strength and toughness was observed. The microstructure of the composite showed that the SiC whisker was destroyed because the SiC whisker degraded due to rapid atom diffusivity at high temperature. The results suggested that some related parameters such as the lower hot-pressing temperature, a short sintering time should be controlled in order to obtain SiC whiskerreinforced ZrB2 composite with high properties.

Abstract: In this study, an anti-plane crack in a functionally graded magnetoelectroelastic materials is investigated. It is assumed that the material properties such as elastic stiffness c44(y), piezoelectric coefficient e15(y), dielectric constant ε11(y), piezomagnetic coefficient α15(y), magnetoelectric coupling coefficient μ11(y) and magnetic permeability υ11(y) vary one-dimensionally on the ycoordinate with a series of functions f(y).An asymptotic analysis is done and the problem is solved by means of singular integral equation technique. The influence of the material inhomogeneity on crack tip stress, electric displacement and magnetic induction intensity factors are studied. The results are considered to reveal the effect of material inhomogeneity and geometry of the crack on the field intensity factors.

Abstract: This paper investigates a moving crack in a nonhomogeneous piezoelectric material (NPM) plate. The mechanical and electrical properties of the plate are considered for a class of functional forms for which closed-form expressions for the moving crack tip electromechanical fields are obtained. Effect of material non-homogeneity and crack moving velocity on the crack tip fields are discussed. The crack moving velocity can increase or decrease the stress intensity factor. The cleavage stress, τθz, however, is always an increasing function of crack moving velocity.

Abstract: Two ZrB2-based composites were fabricated by hot-pressing with vacuum. ZrB2+20vol%SiC and ZrB2+20vol%SiC+8vol%TiB2 were selected as the starting compositions. The microstructures and phase constitutions of the composites were investigated and compared to these of monolithic ZrB2 material. For the ZrB2-based composites, with the addition of SiC particles, the excessive growth of ZrB2 materials is restricted and grain structure is refined. Meanwhile the fracture modes are changed, namely, from transgranular to mixed inter/transgranular. Strengthening mechanism is grain refining and the toughening mechanism is crack deflection, crack branching and grain refining. The role of TiB2 as an addition to the ZrB2 matrix was also examined and discussed.

Abstract: A periodic array of cracks in a functionally graded material under transient mechanical loading is investigated. Anti-plane shear loading condition is considered. A singular integral equation is derived, in which the crack surface displacement is the unknown function. Numerical results are obtained to illustrate the variations of the stress intensity factors as a function of the crack periodicity for different values of the material nonhomogeneity, either at the transient state or at the steady state. The material non-homogeneity can increase or reduce the stress intensity factors. Comparing with the single crack solution, it can be shown that multiple cracking can reduce the stress intensity factor significantly.

Abstract: This paper solves the penny-shaped crack configuration in transversely isotropic solids with coupled magneto-electro-elastic properties. The crack plane is coincident with the plane of symmetry such that the resulting elastic, electric and magnetic fields are axially symmetric. The mechanical, electrical and magnetical loads are considered separately. Closed-form expressions for the stresses, electric displacements, and magnetic inductions near the crack frontier are given.