Experimental investigation on the fracture toughness of Z-pins reinforced composite laminates

The fracture toughness experiments of Z-pin reinforced composite laminates were carried out. Pull-out test of Z-pins of different diameters（0.28, 0.52, 0.80mm）embedded into unidirectional laminate coupons was conducted to measure the curves of Z-pin bridging force versus pull-out displacement. Then, the mode Ⅰ and mode Ⅱ fracture toughness of Z-pinned laminates and unpinned laminates were tested respectively using the double-cantilever-beam (DCB) method and three point edge-notched-flexure (ENF) methods. Comparison was made for the measured mode Ⅰ and mode Ⅱ strain energy release rates between two types of laminates. Strain energy release rates G_ⅠC and G_ⅡC of Z-pin reinforced laminates are higher from 83% to 1110% and from 23% to 438% than those of unpinned laminates respectively. Moreover, the test results denote that enlarging the Z-pin distributive density is more effective to reinforce structural strain energy release rate than enlarging Z-pin diameter at the same volume fraction.