Damage and fracture mechanics analysis of G-11 woven glass-epoxy laminates at cryogenic temperatures

We discuss the cryogenic damage and fracture behaviors of G-11 woven glass-epoxy laminates. In conjunction with the cryogenic fracture toughness test, a two-dimensional finite element analysis was conducted to predict the fracture and deformation for models of the compact tension specimens. Effective elastic moduli were determined under the assumption of uniform strain inside the representative volume element. Hoffman's criterion was selected as the criterion for damage accumulation induced by fiber breakage and matrix cracking was detected by the maximum strain criterion. The strain energy method was adopted to calculate strain energy release rate which leads to determination of stress intensity factor. In order to verify the model, correlations between experimental and analytical results were made, in terms of the load-displacement response and the extent of damage growth. At room temperature and 77 K, good agreements were found between the calculations and the experimental data. The predictions showed that the fracture behavior was influenced by temperature rises associated with individual damage events at 4 K. An apparent fracture toughness, K_i, was calculated for each specimen using the load, P_i, at which a significant change of slope in the damage zone size versus load curve was observed. The K_i value was independent of notch length but increased with specimen size.