Effect of matrix damage on compressive strength in the fiber direction for laminated composites

An original experimental method is proposed to characterize the influence of matrix damage on the compressive strength of laminated composites in the fiber direction using tubes. These composite tubes have a dumbbell-shaped geometry so that rupture occurs in the specimen center without stress concentration. They can be constituted of unidirectional or woven plies aligned with the axial direction. First, a torsional cyclic load is applied in order to damage the matrix. This damage is measured at the tube scale via the reduction in shear modulus. Second, a compressive load is applied up to failure for various damage levels. The method is applied to a woven carbon/epoxy material. Results show that the matrix damage affects significantly the compressive strength in the fiber direction. It is yet observed that longitudinal stiffness is not modified by damage. Finally, a simple model is proposed to describe this decrease of strength vs. matrix damage.