Differential Expansion in Elastic Laminates

Relative movements of different components in a composite structure are partially restrained by the mutual interaction of the components and therefore develop secondary stresses in the structure. Differential expansion in elastic laminates gives rise to shear and normal stresses across the interface between the layers, chiefly confined to a certain length near the free ends. These stresses can be estimated with sufficient accuracy by using the finite element technique. The relative thicknesses of the layers and their elastic properties have a great influence on the magnitude and the distribution of these interface stresses. The shear stress tends to be more concentrated to a point near the free end if the layers are equally stiff. Longitudinal stress and the curvature remain unchanged beyond the end zones and can be determined by the theory of simple bending of beams.