Material parameters for pressure-dependent yielding of unidirectional fiber-reinforced polymeric composites

We study elasto-plastic deformations of unidirectional fiber reinforced polymeric composites (UFPCs) with fibers assumed to deform elastically and the matrix elasto-plastically. The matrix’s and hence composite’s plastic deformations are analyzed by using both the pressure-independent von Mises yield surface and the pressure-dependent Drucker–Prager yield surface and the associated flow rules. In both cases the strain hardening of the matrix is considered and values of material parameters for the matrix are obtained by computing the effective stress versus the effective plastic strain curves from experimental uniaxial stress–strain curves. Values of parameters in the yield surface for the UFPC in terms of those of the matrix and the volume fraction of fibers are found by using a micromechanics approach. Wherever possible, the computed results are compared with the corresponding experimental findings available in the literature. Significant contributions of the work include providing a methodology for determining values of elasto-plastic material parameters for a UFPC from those of its constituents and their volume fractions, and giving expressions in terms of volume fractions of fibers for material parameters appearing in the yield surface of the composite.