Abstract
In this paper, we determined a state of stress, which verifies the Cauchy equations of equilibrium, the conditions of continuity on the surfaces between layers and boundary conditions for a sandwich beam subjected to tensile test. We customized the relations, previously obtained, for a composite beam consisting of two layers. Using a mediation formula for strain and stress, we obtained a new formula for the calculus of the longitudinal modulus of elasticity, when the constituent materials have different Poisson ratios. Considering the maximum stress reached in the layers, we determined a formula, which helps us to determine the order in which the two layers will break. We did experimental measurements for test samples made from polyesteric resin, reinforced with fiber glass fabric, carbon and carbon-kevlar. Keywords: composite materials, characteristic curve, elasticity modulus