Free edge stress propagation in composite laminates

Theoretical analyses show how sequences of similar moduli are able to take characteristic unidimensional propagations† † Such a term here indicates a trend in the space of the considered media of repeated characteristic static stresses and/or elastic displacements by damped oscillations. of static stresses and elastic displacements through self-equilibrated sections. The present work constitutes a numerical attempt at solving such theories, paying particular attention to the free edges phenomena which also propagate in a bidimensional way, in composite laminates. Rectangular plates, subjected to longitudinal uniform traction stresses on two sides and free at the remaining sides, made by a symmetric overlap of orthotropic laminae, are schematized by NASTRAN tridimensional elements. The analysis shows how overlaps presenting stress distributions of a magnitude smaller than the traction amount, but loading the adhesive interlaminar film and also causing delaminant effects, exist near the free edges and propagate from them with damped oscillations. On the same plates the effect of centred holes, having sufficiently small diameter not to suffer the effect of the edges, is investigated. Considering the lay up has shown the highest delaminant stresses concentration is at the free sides of the solid plates, in the neighbourhood of the holes bidimensional stress propagations are shown. They show their greatest gradients in radial directions, each are characteristic of a specific stress and different from that of any other. The stress propagation also shows, that in laminates of equal thickness and with identically loaded, delaminant effects, gradients are greater for the holes having smaller diameter, which correspond however to decreasing stresses, so that storing up stress is less likely to cause fatigue in the environment.