Intralaminar fracture toughness of a cross-ply laminate and its constituent sub-laminates

The intralaminar mode I fracture toughness values for a M55J/M18 carbon/epo xy cross-ply laminate [0 degrees /90 degrees](15) (alternate 0 and 90 degre es layers) and its constituent sub-laminates, namely the [0 degrees](30) an d [90 degrees](30) laminates are theoretically evaluated on the basis of a modified crack-closure integral (MCCI) method corresponding to the fracture loads obtained by testing C(T) specimens. A simple relationship between th e intralaminar fracture toughness at the specimen level of a cross ply and its constituent sub-laminates is presented. Test data for fracture loads an d crack-opening displacements at the opposite end (far end) to the crack ti p of the three types of C(T) specimens are obtained. A comparison of fractu re toughness values K-1c and crack-opening displacements obtained from test s with theoretical predictions by finite-element analysis shows good agreem ent for the type of laminates considered. Comparison of the analytically de termined K-1c of the cross-ply C(T) specimen based on the new relationship using the respective values of K-1c of its constituent C(T) specimens shows good agreement with test data. (C) 2001 Elsevier Science Ltd. All rights r eserved.