Abstract
The near-threshold growth of delamination fatigue cracks under different stress ratios was investigated with unidirectional laminates made from ICI APC-2(AS4/PEEK). Tests of mode I delamination fatigue crack propagation were carried out by using double cantilever beam specimens. The crack growth rate decreased with crack extension under the constant maximum energy release rate (Gmax-constant) test. The true growth law which is not affected by fiber bridging was obtained by the growth rate at zero-increment of the crack length from a series of Gmax-constant fatigue test. Then, the increase of the crack growth resistance caused by fiber bridging was evaluated. Although the saturated level of this increase was almost the same for both the fatigue and static tests, the length of the saturation for this increase was much longer for the fatigue test than that for the static test. The differences of the crack growth behavior and the stress ratio dependency between the Gmax-constant test and the conventional Gmax-decreasing test were discussed on the basis of the mechanism consideration.
