Characteristics of the stress relaxation in the thinned two-phase multilayer materials

In the two-phase multilayer bulk material, strong inner stress field may ex ist if the thermal expansion coefficient of one phase is distinctly differe nt from that of another phase. When a sample is thinned in cross section of the bulk material for studying by transmission electron microscopy (TEM), stress relaxation will occur in the sample. Thus, stress and strain states in the sample are different from that in the bulk material. In this paper, the finite element method was employed to analyze the characteristics about stress relaxation in the sample when the sample was separated from the bul k material. Results show that: larger residual stresses still remain near t he interface; the shear stress field is formed at the local interface regio n near the free surface, and; stresses change drastically near the intersec tion of interface and free surface. When the ratio of the sample thickness to the layer thickness is small, the stress sigma(zz) (perpendicular to the sample surface) relaxes throughout the sample thickness in the region remo te from the interface, and this stress remains only near the interface. Whe n the ratio of the sample thickness to the layer thickness is large, stress relaxation occurs only near the free surface. (C) 1999 Elsevier Science S. A. All rights reserved.