Abstract
In this paper we determine a field of stress, which verifies the Cauchy equations of equilibrium, the conditions of continuity on the surfaces between layers, and boundary conditions, for a sandwich bar, with symmetrical distribution of layers, subject to traction. We have considered the relationships, previously obtained, for a composite bar built of three layers. Using a mediation formula for deformations and stress, we obtained a new formula for calculating the longitudinal elasticity modulus, in the case in which the constituent materials have different coefficients of transversal contraction. We realized the experimental measurements for test samples from polyesteric resin, reinforced with woven of fibers glass, carbon and glass-carbon. Keywords: composite materials, characteristic curve, elasticity modulus