Micro-failure prediction of the strength of composite materials under combined loading

Micro-failure criteria which were previously proposed for the prediction of strength and fatigue failure of composite materials are generalized for capturing the trend of the increase in shear strength with moderate transverse normal compressive stress. The generalization involves the introduction of the Coulomb frictional law, which follows from physical considerations, to accommodate this trend. Comparisons of the predicted failure of carbon/epoxy and glass/epoxy laminae under combined transverse normal and shear stress with measured data, support the validity of the proposed micromechanical approach.