Size effect in transverse compressive strength of composites analyzed by the fixed crack model

Presented in this study is a numerical analysis of the size effect in the transverse compressive strength of unidirectional (UD) composites by employing the fixed crack model. The model is calibrated and verified using available coupon level test data on transverse compression of a carbon-epoxy T700/MTM57 unidirectional composite. Then, it is used to predict the failure of geometrically scaled notched specimens of different sizes, each subjected to transverse compression. Two different notch orientations are considered. All specimens are predicted to fail in a geometrically similar fashion by an inclined shear crack starting from the notch tip. The predicted size effect in the nominal strength is fitted well by Bažant's size effect law and is consistent with the estimated size of the fracture process zone. Thus, the results provide strong evidence for the applicability of quasi-brittle fracture mechanics in propagating transverse compressive failures in UD composites. Moreover, a strong anisotropy in the fracturing behavior, as well as the degree of quasi-brittleness, is demonstrated. Therefore, the findings emphasize the need for characterization of these effects via suitable experiments.