Evaluation of the interlaminar fracture toughness on composite materials using DCB test on symmetric and unsymmetric configurations

A procedure to measure the interlaminar fracture toughness of a composite material is proposed in this work. This property is evaluated using the DCB test, the new formulation developed being applicable to small thicknesses and nonsymmetric configurations. The GC evaluation proposed in this paper does not require to know the evolution of the crack length with the load. This fact facilitates the performance of the test and allows complex situations (crack jumps, tests at high temperature,...) to be taken under consideration. An experimental campaign has been carried out on four different configurations, three symmetric (2 + 2, 4 + 4 and 8 + 8 layers) and one nonsymmetric (4 + 8 layers). The results show that, when they are appropriately treated, the values obtained are independent of the number of layers of the adherents and even of the symmetry of the joint, validating the use of the DCB test on nonstandardized coupons.