PROBABILISTIC INITIAL FAILURE STRENGTH OF HYBRID AND NON-HYBRID LAMINATES.

The initial failure strength or strain at the failure of low elongation layers is analysed by the statistical approach based upon the weakest link model. First ply failure is adopted as a criterion for the initial failure of the laminate. An expression for determining the first ply failure strength has been derived and this expression can be reduced to a volumetric relation as a special case. It is also shown that the initial failure strength or strain is greater in composites composed of low elongation and high elongation materials than in the pure low elongation composite. This is the result of the 'size effect', that is the failure probability is lower in the composite with the smaller size of low elongation material. A good agreement between the theoretical and experimental results is achieved.