Effect of Fiber Bridging on Growth Behavior of Mode I Interlaminar Fatigue Cracks in High Strength GFRP

Abstract

The mode I crack growth behavior from delamination was investigated with two kinds of laminates, UD laminates (made of unidirectional laminates) and C laminates (made of unidirectional laminates and cloth laminates), of high strength glass fiber reinforced plastics (GFRP). Crack growth tests were carried out by double cantilever beam specimens under cyclic and monotonic loadings. The fracture toughness at the onset of crack propagation, CIc., was not influenced by the lot of laminates and nearly equal for UD laminates and C laminates. On the other hand, the increase of the fracture toughness with crack extension, GIR, was very much dependent on the lot, and the value for C laminates was much higher than that of UD laminates. Under cyclic loading with a stress ratio of R=0.1, the fatigue crack propagation rate expressed in terms of a power function of the maximum crack-tip value, GI tipmax, of the energy release rate was nearly identical in UD and C laminates. The increase of the bridging component of the energy release rate, GIbridgemax /GI max, with crack extension was dependent on the lot and the kind of laminates. Fractographic observation of UD laminates showed mode II crack propagation on the surface of fibers, while mode I crack propagation in resin. In C laminates, crack propagation path was on the interface of cloth laminates and fiber bridging caused by fibers of cloth laminates.