In this study, a micromechanics-based method is developed to predict the off-axis strength of unidirectional linear elastic laminae. These composites fail by matrix cracking along a plane parallel to the fiber direction. The stresses in the matrix are calculated using a local stress analysis based on a concentric cylinder model. This model consists of a unique fiber embedded in matrix; both constituents are represented by cylinders. A finite element model is also constructed and the results of the two models compared. The stresses and strains from the concentric cylinder model are averaged over the volume of the matrix and used in a local failure function. This failure function has the form of a reduced and normalized strain energy density function where only transverse and shear terms are considered. The off-axis strength prediction method is validated using data from the literature.

This failure function will be used in the near future for composites with a matrix having nonlinear properties. Experimental tensile tests on steel-cord/rubber laminae and laminates as well as on the nonlinear rubber matrix were performed. Stress-strain behavior and off-axis strength data were obtained. An approach for off-axis strength prediction for these laminae is defined based on a finite element stress analysis. The finite element analysis approach is motivated by the one used for linear composites.