Universidade do Porto

The aerospace industry is committed to improve the performance of aircraft whilst reducing emissions and weight. Such a goal can be achieved by the use of composite materials. The design procedure used for advanced composite structures relies on a 'building-block ' approach, where a large number of experimental tests are performed. The use of advanced analytical or numerical models in the prediction of the mechanical behavior of composite structures can significantly reduce the cost of such structures. Strength-based failure criteria are commonly used to predict failure in composite materials. A large number of continuum-based criteria have been derived to relate stresses and experimental measures of material strength to the onset of failure [1]-[2]. Failure criteria predict the onset of the several damage mechanisms occurring in composites and, depending on the material, geometry and loading conditions, may also predict structural collapse. For composite structures that can accumulate damage before structural collapse the sole use of failure criteria is not sufficient to predict ultimate failure. Simplified models, such as the ply discount method, can be used to predict ultimate failure, but cannot represent with satisfactory accuracy the progressive reduction of the stiffness of a laminate as a result of the accumulation of matrix cracks