AN ASYMPTOTIC ANALYSIS OF METHODS FOR PREDICTING THE FRACTURE TOUGHNESS OF MULTIAXIAL CARBON FIBER COMPOSITE LAMINATES USING THE ELASTIC CONSTANTS OF THE 0° PLIES

Carbon fiber composite laminates are an important alternative to metal in many mechanical structural applications. Carbon fiber composite laminates usually have multidirectional plies with different angles. In this study, a simple analytical model is derived to predict the notch strength of these multidirectional plies from the unidirectional strength of the 0 degrees ply. The first method considers the orthogonal analysis of the forces introduced in each ply at the Cartesian coordinates in each of the 2 axes with their direction, and then calculates the resulting forces. The second method considers the percentage of layers inside the laminates and then orthogonally analyzes the induced forces on the entire laminate sheets. The resulting stress induced by these forces is calculated according to the theory of maximum failure shear or principal stress. In addition, the fracture toughness G(IC) was predicted based on the strength of the unnotched laminates calculated by previous methods. In addition, the size effect of the open-hole specimen was measured based on the predicted fracture toughness and strength of the unnotched laminates. The model was compared with available experimental and other published models. The optimum values for the two methods of fracture toughness were determined. The average percent accuracy of size effect prediction based on the first method is 3.24%, while it is 6.82% for the second method.