Mixed mode I/II interlaminar initiation fracture toughness of a secondary bonded pultrusion composite laminate

Quasi-static fracture toughness tests were carried out on four types of beam specimens in order to determine the mixed mode I/II initiation fracture toughness of a secondary bonded laminate composed of uni-directional pultrusion composite plies. The tests included the double cantilever beam (DCB) test for pure mode I; the mixed mode end loaded split (MMELS) test for a mode I dominant mixed mode I/II ratio; the mixed mode bending (MMB) test for a mode II dominant mixed mode I/II ratio; and the calibrated end loaded split (C-ELS) test for pure mode II. Following the tests, the fracture surfaces were examined and related to the test behavior of each specimen. The results of the fracture toughness tests were used to establish a mixed mode I/II initiation fracture toughness criterion. Several criteria were examined.