A 3-D finite deformation anisotropic visco-plasticity model for fiber composites

A 3-D finite deformation anisotropic visco-plasticity model is presented fo r fiber composites in total Lagrangian co-ordinates. The plastic potential function is given by a quadratic function in stresses in the local co-ordin ates system of the lamina. The model is used to derive the anisotropic plas tic constitutive relation of a woven composite made of S-2 glass fibers emb edded in polyester resin with approximately 60% by weight of fibers. The co efficients of the constitutive model are experimentally determined through off-axis tension tests and out-of-plane shear tests. Off-axis tension tests are carried out by varying the angle between the fiber orientation and loa ding direction. The measured stress-strain curves are used to derive a mast er effective stress-effective plastic strain curve, which is described by t wo power laws. A modified Arcan fixture is used to carry out pure shear tes ts to determine the out-of-plane shear coefficient. Compression tests are c arried out to establish the material compressive response in the plane of t he lamina and along the fiber direction. The anisotropic plasticity model i s integrated into the in-house finite element code FEAP98. Numerical analys es are carried out for the off-axis tension tests and compression tests. Th ese analyses show that the model reasonably predicts the constitutive respo nse of woven GRP composites in confirmation with the experimental data. The model further incorporates strain rate and temperature dependence on the a nisotropic plastic flow constitutive law. Ballistic penetration simulations are carried out using the integrated code, The velocity at the back surfac e of the composite target, obtained by analyses, is compared with the data measured experimentally using interferometry. Insight into the failure proc ess is obtained through analysis of different energy dissipation mechanisms .