Fibre/matrix stress transfer through a discrete interphase: 2. High volume fraction systems

The effect of plasticity on the reinforcing efficiency of a broken fibre, and the magnitude of the strain concentration experienced by the surrounding fibres, has been assessed by the use of a 3-dimensional finite-element model. It was found that the occurrence of plasticity in the matrix markedly reduced the strain concentration in fibres adjacent to a fibre fracture. The effect of increasing the fibre volume fraction on the level of strain concentration was examined and it was found that when deformation was elastic, at low applied strain, a higher fibre volume fraction led to an increase in the strain concentration. However, when plastic deformation occurred, the strain concentration factor was significantly lower and increasing the fibre volume fraction had a negligible effect. The influences of soft or stiff interphases between fibre and matrix were also studied and, during elastic deformation, these were found to be largely insignificant in determining the stress transfer processes, for the interphase thickness studied. At higher strains, the occurrence of plastic deformation in either the matrix or interphase was found to dominate the strain-transfer process and, therefore, the strain concentration. The reasons behind these dependencies are discussed and their effect on the failure of bulk composites considered.