Effect of the thickness on the fracturing behavior of discontinuous fiber composite structures

In this study, we investigate experimentally and numerically the mode I intra-laminar fracture and size effect of Discontinuous Fiber Composites (DFCs) as a function of the structure thickness. Fracture tests on geometrically-scaled Single Edge Notch Tension (SENT) specimens show a notable size effect on the nominal strength of DFCs. By integrating equivalent fracture mechanics and stochastic finite element modeling we estimate, for the first time, the fracture energy and the effective size of the Fracture Process Zone (FPZ) as a function of the thickness of the DFC structure. From the integrated analysis, it is found that the fracture energy depends significantly on the structure thickness. It is shown to increase gradually with increasing thickness, t, and to saturate for t >= 3 mm to a value of 57.77 N/mm, which is 4.81 times larger than a typical aluminum alloy. For thicknesses lower than 1.1 mm, corresponding to an average number of platelets through the thickness of roughly 8, it was found that the fracturing process can often be triggered by weak spots in the structure rather than the stress-free notch.