THICKNESS EFFECT OF DCB SPECIMEN ON INTERLAMINAR FRACTURE TOUGHNESS IN CARBON/EPOXY COMPOSITES

In this work, the influence of specimen thickness on interlaminar fracture toughness in delamination of unidirectional carbon/epoxy laminates is presented. Specimens of three different thicknesses: 3.99, 5.27 and 6.65 mm are tested under the quasi-static condition to measure interlaminar fracture toughness GIc, in terms of strain energy release rate. It is found that higher fracture toughness values are obtained from thinner DCB specimens. While the GIc initiation values are dependent on the specimen thickness, whereas the propagation values of GIc increased continuously with crack length. Analysis of test specimens in mode I fracture is made by using three data reduction schemes based on modified beam theory, a compliance calibration method, and a modified compliance calibration method. Fiber bridging is also identified during experiments which lead to higher GIc in thin specimens.