Stress concentration factor in matrix of a composite reinforced with transversely isotropic fibers

The stress concentration factor in the matrix of a fibrous composite reinforced with transversely isotropic fibers is determined upon constituent elastic properties as well as the fiber volume fraction available before fabrication of the composite. The matrix in situ transverse strengths are then defined from its original counterparts divided by the stress concentration factor, which are further used together with the other original constituent property parameters for calculating strengths of the composite in terms of the bridging model. The thus obtained strength envelopes of several unidirectional composites subjected to combined bi-axial loads are compared with independently measured results. Favorable correlation indicates that a composite ultimate strength can be reasonably well estimated without using any experimental data of the composite itself. The article clearly shows that an accurate prediction for a composite strength must take all of the three influencing factors, i.e. stress concentration, matrix inelasticity, and thermal residual stresses, into account. It is further demonstrated in the article that the stress concentration factor with transversely isotropic fibers involved can be sufficiently accurately approximated by a much simpler stress concentration factor formula derived upon isotropic fiber reinforcement.