Influence of matrix plasticity on local stress concentrations near loaded fiber breaks

In this study, stress concentrations near loaded and initial fiber breaks are analyzed for unidirectional composites with matrix yielding and interfacial sliding. To this end, by performing detailed 3D finite element analysis, it is demonstrated that significant nonproportional stressing occurs in the matrix near loaded fiber breaks in contrast to initial breaks, and that the nonproportional stressing induces almost elastic shear deformation in the matrix outside the first nearest-neighbor fibers of loaded fiber breaks. Then, the 3D shear-lag analytical solution derived by the present authors is modified to be applicable to low fiber volume fractions and is employed to dicuss how the nonproportional stressing in the matrix influences the stress concentrations near loaded fiber breaks. The 3D analytical solution is shown to be applicable to loaded, as well as initial, fiber breaks, if the matrix shear modulus in the solution is prescribed by taking account of the nonproportional stressing. It is thus concluded that the nonproportional stressing in the matrix may considerably lower the stress concentrations near loaded fiber breaks.