A modified ultimate failure criterion and material degradation scheme in bridging model prediction for biaxial strength of laminates

The first worldwide failure exercise (WWFE-I) indicated that the bridging micromechanics model exhibited a unique feature in calculating internal thermal stresses in the constituent fiber and resin materials of a laminated composite. Once applied to laminate strength prediction, however, the model only gave moderate correlation with the experiments. In this article, a material degradation scheme and a modified ultimate failure criterion for laminates are incorporated into the bridging model to improve its predictive capacity. Pure resin inter-layers are also introduced to simulate the effect of interfaces in between the lamina plies. With these modifications, much more accurate predictions have been obtained for the majority of the exercise problems, especially for the ultimate strengths and deformations of the multi-directional laminates. The correlation of the present theory predictions with the experiments is even better than that of any other theory predictions made in the exercise.