Papers by Author: Shou Wen Yu

Abstract: A crack problem in a micropolar piezoelectric solid is considered. By using simplified constitutive relations, the problem can be reduced to the solution of a set of Cauchy singular integral equations with the help of Fourier integral transform technique. Numerical results for stress intensity factors, couple stress intensity factors and electric displacement intensity factors show that micropolar theory can be expected to explain certain size effects in piezoelectric solids.

Abstract: An axisymmetric problem of interaction of a rigid rotating flat ended punch with a transversely isotropic linear piezoelectric half-space is considered. The contact zone consists of an inner circular adhesion region surrounded by an outer annular slip region with Coulomb friction. Beyond the contact region, the surface of the piezoelectric half-space is free from load. With the aid of the Hankel integral transform, this mixed boundary value problem is formulated as a system of dual integral equations. By solving the dual integral equations, analytical expressions for the tangential stress and displacement, and normal electric displacement on the surface of the piezoelectric half-space are obtained. An explicit relationship between the radius of the adhesion region, the angle of the rotation of the punch, material parameters, and the applied loads is presented. The obtained results are useful for characterization of piezoelectric materials by micro-indentation and micro-friction techniques.

Abstract: In the present paper, continuum fracture mechanics is used to analyze the Smart-Cut process, a recently established ion cut technology which enables highly efficient fabrication of various silicon-on-insulator (SOI) wafers of very high uniformity in thickness. Using integral transform and Cauchy singular integral equation methods, the mode-I and mode-II stress intensity factors, energy release rate and crack opening displacements are derived in order to examine several important fracture mechanisms involved in the Smart-Cut process. The effects of defect interaction and stiffening wafer on defect growth are investigated. The numerical results indicate that a stiffener/handle wafer can effectively prevent the donor wafer from blistering and exfoliation, but it slows down the defect growth by decreasing the magnitudes of SIFs. Defect interaction also plays an important role in the splitting process of SOI wafers, but its contribution depends strongly on the size, interval and internal pressure of defects. Finally, an analytical formula is derived to estimate the implantation dose required for splitting a SOI wafer.

Abstract: In this paper, a phenomenological, nonlinear constitutive relation of ferroelectric ceramics is established by considering the fact that domain switching happens gradually with the external loading. A simplified gradual switching model is suggested and implemented into the constitutive law of ferroelectric materials. The volume fraction of domain switching is used as the internal variable in the model, and its evolution equation with mechanical/electrical loading is given. Comparison with experimental results shows that this simple constitutive model can predict the nonlinear hysteresis responses of ferroelectric materials.

Abstract: It is still an open problem how the thermal effect influences the fracture behavior of piezoelectric materials especially under cycling electrical loading. Experimental observations have found that the fracture toughness of piezoelectric solids under electric loading may be greatly different from that under mechanical loading. A pronounced rise of temperature may be caused either by mechanical or by electric loading. In this paper, the thermal effects and energy dissipation mechanism in cracked piezoelectric materials under cyclic-electric-loading have been studied. The temperature rise is derived under the assumption of decoupling between thermal and electromechanical fields and the influences of frequency and the shape of electric wave on the temperature rise are quantitatively analyzed.