Environmental degradation of interlaminar shear strength in carbon/epoxy composites

Abstract

The effect of environmental and loading conditions on the degradation of Interlaminar Shear Strength (ILSS) of the carbon-epoxy composite specimens was studied. The hygrothermal conditions capture the synergistic effects of field exposure and extreme temperatures. A short beam shear test (SBST) was performed to determine the Interlaminar Shear Strength (ILSS) of environmentally aged composite specimens in accordance with ASTM D2344-84. Initially, a standard two-dimensional cohesive layer constitutive model was employed in order to simulate the experiment using an in-house FEA code (NOVA-3D). Numerical instabilities, encountered using the standard cohesive layer model, were overcome by incorporating viscoelastic regularization in the constitutive equations of the cohesive layer. This modification also enabled the analysis to continue beyond the point of peak failure load. The model was able to accurately simulate the load vs. displacement behavior of most of the SBST samples aged under various hygrothermal and synergistically applied stress conditions. Further, the effect of displacement rate on the ILSS of specimens was studied using NOVA-3D. The model indicated a strong dependence of viscoelastic cohesive strength on the displacement rate. Regrettably, the predicted rate dependence could not be verified experimentally.