Fiber reinforced polymer (FRP) composites are a heavily sought-after material for light-weighting components in next generation vehicles due to their high specific strength and stiffness. Traditional laminates have relatively weak interlaminar strength and are prone to delamination, and this is especially the case when a delamination crack already exists. Quasi-3D (Q3D) braided composites seek to solve this issue by weaving the bias tows around the axial tows of the adjacent (above and below) plies.The [0°/60°/-60°] UD and Q3D carbon composites are investigated in this study for their relative in-plane isotropy. Mode I and mode II interlaminar fracture toughness tests were conducted on UD and Q3D samples.In mode I experiments, the samples were continuously loaded to full beam split using the double cantilever beam (DCB) method to obtain the fracture toughness throughout the sample. The Q3D composite shows a large increase in fracture toughness once the crack stabilizes and the interlaminar tows become engaged.In mode II testing under end-notch flexural (ENF) test conditions, the Q3D composite shows a significant increase in fracture toughness after a pre-crack has formed and the interlaminar tows have been engaged. The 4ENF test also proves to be a good method for creating a mode II resistance curve that could only be achieved through extensive testing through traditional methods.
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