Zhengjin Wang

Effect of initial stress on the propagation behavior of Love waves in a layered piezoelectric structure

Abstract The propagation behavior of Love waves in a layered piezoelectric structure with an initial stress is investigated in this article. It involves a thin piezoelectric layer bonded perfectly to an elastic substrate. Solutions of the mechanical displacement and electrical potential function are obtained for the piezoelectric layer and elastic substrate by solving the coupled electromechanical field equations. The phase velocity equations of the Love wave propagation and the stress fields in the layered piezoelectric structure are obtained for electrical open and short cases on the free surface, respectively. The effect of the initial stress on the phase velocity, the stress fields and the coupled electromechanical factor are discussed, respectively. Three sets of piezoelectric layer–elastic substrate systems are considered, i.e. BaTiO3 ceramic layer–borosilicate glass substrate, PZT-5H ceramic layer–borosilicate glass substrate, and PZT-5H ceramic layer–SiO2 glass substrate. It is seen that the phase velocity of the Love wave propagation decreases with the increase of the magnitude of the initial stress. The coupled electromechanical factor increases remarkably, as the magnitude of the initial the stress is greater than 100 MPa. This is useful for the design of acoustic surface wave devices.

Large Deflection of Geometrically Asymmetric Metal Foam Core Sandwich Beam Transversely Loaded by a Flat Punch

The objective of this work is to study the large deflection of geometrically asymmetric metal foam core sandwich beam under transverse loading by a fiat punch. A yield criterion is proposed for geometrically asymmetric metal foam core sandwich structures, and then analytical solution for the large deflection of a fully clamped slender sandwich beam is obtained, in which the interaction of bending and stretching induced by large deflection is considered. Also, finite element (FE) analysis is carried out. Comparisons of the analytical solution with numerical results are presented and good agreements are found. The effects of asymmetric factor, core strength and loading punch size on the structural response of asymmetric sandwich beam are discussed in detail. It is shown that the axial stretching induced by large deflection has significant effect on the load-carrying and energy absorption capacities of geometrically asymmetric sandwich structure, but the effect of asymmetry is negligible as the deflection is larger than the depth of the sandwich beam.

A YIELD CRITERION AND PLASTIC ANALYSIS FOR PHYSICALLY ASYMMETRIC SANDWICH BEAM WITH METAL FOAM CORE

A yield criterion for physically asymmetric sandwich cross-sections is proposed in this paper. Using the yield criterion, analytical solutions for the large deflections of fully clamped asymmetric slender sandwich beams transversely loaded by a flat punch at the midspan are derived considering the core strength effect and interaction of bending and axial stretching. Finite element (FE) method is employed to predict the large deflection behavior of the sandwich beams. Good agreement is achieved between the analytical predictions and FE results. Effects of asymmetric factor, core strength and loading punch size are also discussed. It is demonstrated that core strength and loading punch size have significant influences on the load-carrying and energy absorption capacities of physically asymmetric metal sandwich beams while the asymmetry effect could be neglected when the deflection exceeds sandwich beam depth.

Effect of a biasing electric field on the propagation of antisymmetric Lamb waves in piezoelectric plates

This paper is concerned with the effect of a biasing electric field on the propagation of Lamb waves in a piezoelectric plate. On the basis of three dimensional linear elastic equations and piezoelectric constitutive relations, the differential equations of motion under a biasing electric field are obtained and solved. Due to the symmetry of the plate, there are symmetric and antisymmetric modes with respect to the median plane of the piezoelectric plate. According to the characteristics of symmetric modes (odd potential state) and antisymmetric modes (even potential state), the phase velocity equations of symmetric and antisymmetric modes of Lamb wave propagation are obtained for both electrically open and shorted cases. The effect of a biasing electric field on the phase velocity, electromechanical coupling coefficient, stress field and mechanical displacement of symmetric and antisymmetric Lamb wave modes are discussed in this paper and an accompanying paper respectively. It is shown that the biasing electric field has significant effect on the phase velocity and electromechanical coupling coefficient, the time delay owning to the velocity change is useful for high voltage measurement and temperature compensation, the increase in the electromechanical coupling coefficient can be used to improve the efficiency of transduction.

Indentation of sandwich beams with metal foam core

Abstract The quasi-static indentation behavior of sandwich beams with a metal foam core was investigated. An analytical model was developed to predict the large deflections of indention of the sandwich beams with a metal foam core subjected to a concentrated loading. The interaction of plastic bending and stretching in the local deformation regions of the face sheet was considered in the analytical model. Moreover, the effects of the shear strength of the foam core on the indentation behavior were discussed in detail. The finite element simulations were preformed to validate the theoretical model. Comparisons between the analytical predictions and finite element results were conducted and good agreement was achieved. The results show that the membrane force dominates indentation behavior of the sandwich beams when the maximum deflection exceeds the thickness of the face sheet.