GEOMETRICALLY NONLINEAR STRESS DEFLECTION RELATIONS FOR THIN-FILM SUBSTRATE SYSTEMS

A previously developed geometrically nonlinear stress-curvature relati on is expanded in this paper to allow for a less restrictive approxima tion of the midplane strains in a thin film/substrate system. The prev ious analysis is based on a minimization of the total strain energy an d predicts a bifurcation in shape as the magnitude of intrinsic film s tress increases. It is reviewed here and three new cases are presented . Expanding the approximating polynomials for the normal midplane stra ins epsilon(x)0 and epsilon(y)0, has a small effect on the solution. H owever, allowing the midplane shear strain, gamma(xy)0, to be nonzero has a pronounced effect on the solution, particularly in the stress re gion near the bifurcation point.