Shear Nonlinearity Behaviour of Fibrous Composites under Cyclic Loading

The in-plane shear stress-strain relationship of UD fibre-reinforced composites is a well-known example in which nonline-arity behaviour plays a dominant role while the linear-elastic regime is relatively small. This paper describes a new phe-nomenological damage model for prediction of the shear behaviour. The observed nonlinear behaviour may well be the result of combined effects of nonlinear elasticity، viscosity، plasticity and microscopic damage and some of these processes in the material are irreversible in nature. The model applies to any phase of the cyclic loading، such as loading، unloading، reversed loading، unloading from reversed loading and reloading up to failure. The model has been compared with test results. Excellent agreements between the prediction and experimental results have been observed in all respects. In order to incorporate this nonlinear shear model in a comprehensive material model so that it can be applied in general structural analysis. A material user subroutine UMAT has been written for this model and all results obtained by this user subroutine via commercial finite element code ABAQUS.