Interlaminar fracture toughness of a graphite/epoxy multidirectional composite

In this paper, an experimental investigation on interlaminar fracture behavior and fracture toughness of a graphite/epoxy multidirectional composite laminate is presented using end-notched flexure specimens. The 0/0 interfaces are considered. The interlaminar fracture toughness is obtained and compared using three data reduction methods, i.e., the area method, classical laminated plate theory, and finite element analysis. Results show that the toughness value depends on the data reduction method used. Two different crack-length-to-span ratios are chosen to study how the stable or unstable crack extension influences the toughness measurement. It is observed that the toughness obtained from the tests of stable crack extension is appreciably higher than that from the tests of unstable crack extension. It is also seen that friction resulting from contact of crack surfaces greatly affects the measured roughness in the case of stable crack extension. In addition, effects of the specimen geometry and fiber orientation on the interlaminar fracture toughness are also evaluated. [S0094-4289(00)02804-8].