Material and structural response of polymer-matrix fibre-reinforced composites

This paper presents a pressure-dependent three-dimensional constitutive law to predict failure for laminated composites. The nonlinear constitutive response in shear and in the transverse and through-the-thickness directions, which is measured experimentally, is incorporated directly into the model. In addition, secant stiffnesses are dependent on the state of hydrostatic pressure and on the general state of strain. The failure criteria distinguish between matrix failure, fibre kinking and fibre tensile failure. In-situ strengths are used for matrix failure. Propagation of failure takes into consideration the fracture energy associated with each failure mode and, for matrix failure, the accumulation of cracks in the plies. A detailed discussion is undertaken of the mismatch between the available experimental data and the physical properties required to characterise the constitutive response up to final failure. The model is employed to make blind predictions of the triaxial failure envelopes and stress–strain curves of all 12 test cases provided by the organisers of the second World-Wide Failure Exercise.