Combining Elastic Brittle Damage with Plasticity to Model the Non-linear Behavior of Fiber Reinforced Laminates

The present work is concerned with modeling the non-linear behavior of continuous fiber reinforced laminates with a special emphasis on loading conditions that lead to high ply shear stresses. Typically, the modeling of non-linear laminate behavior focuses on damage mechanics approaches and assumes that the non-linearity is caused by brittle matrix cracking. Based on the correlation of experimental data and modeling results, this assumption seems to hold true for load cases in which layers experience mainly tensile stresses. Under shear dominated loads, however, it has been found that the agreement between tests and model predictions is less satisfactory. Additionally, considerable permanent strains develop under such loading conditions that cannot be explained by brittle mechanisms alone. Here, a model is presented that combines damage mechanics with a plasticity law to capture both degradation of stiffness due to cracking and residual strains accumulated under shear loads. It is assumed that damage starts to develop close to the first ply failure load and any non-linear behavior prior to the onset of damage is attributed to plastic shear strains. Predictions of the model are compared to experimental data and are shown to give improved correlation to experiments under shear dominated loading. By taking residual stresses into account, the model is also able to explain discrepancies in the shear behavior derived from two different test methods. Furthermore, the combined damage/plasticity model captures the accumulation of residual strains, the non-linear behavior observed in uniaxial transverse compression tests, and the influence of transverse normal stress on the non-linear shear behavior reported in the literature.