Two Constitutive Models Based on the Unified Shear Curve to Predict a Nonlinear Response of Fabric Carbon Fibre-Reinforced Plastics in the 2D Stress State

In some case, polymer composites can exhibit a significantly nonlinear deformation behavior. The conventional approach to estimating the strength of a composite structure, in which the material is considered linearly elastic up to failure, can lead to significant errors and overloading. In this work, we examine the effectiveness of two relatively simple models taking into account the nonlinear deformation of the fabric composite with a thermosetting matrix. Both models are based on the assumption that the shear stress–strain curve is independent of the 2D stress state. On the one hand, this significantly simplifies the process of determining model parameters, because only standard tensile and shear tests are used. On the other hand, it is necessary to clearly understand the applicability limits of such models. Verification of deformation models was carried out based on the results of off-axis tensile tests on carbon fabric-reinforced composite specimens as well as composite specimens with the ±15° and ±30° lay-ups of the carbon fabric. Comparison of the calculated and experimental stress–strain curves shows that this approach can be successfully used in the analysis of the nonlinear mechanical behavior of fabric composites made of thermosetting polymers under shear strains up to 5% without significant errors.