A simple nonlinear constitutive model based on non-associative plasticity for UD composites: development and calibration using a Modified Arcan Fixture

A simple nonlinear constitutive model based on non-associative plasticity for unidirectional (UD) composites is developed and calibrated using a Modified Arcan Fixture (MAF) and Digital Image Correlation (DIC). The plasticity model accounts for the nonlinear response of unidirectional composites subjected to multiaxial loading, assuming transverse isotropy and negligible plasticity in the fibre direction. The different responses in transverse tension and compression are accounted for by a Drucker?Prager type yield function to include transverse pressure sensitivity. It is shown that using an associative flow rule leads to the prediction of non-physical plastic strain components, whilst the use of a non-associative flow rule resolves the deficiency of the associative model. The non-associative model is calibrated and verified against biaxial test data obtained from glass/epoxy specimens using the MAF, as well as against off-axis test data available in the literature for two additional composite material systems. The nonlinear stress-strain curves for unidirectional composites subjected to multiaxial stress states predicted by the model are in good agreement with all three sets of experimental data, thus demonstrating the predictive capabilities of the proposed model.