Criterion for the final failure of a pin joint with bearing damage in CFRP laminates under cyclic tensile loading

A mechanically fastened joint in Carbon Fiber Reinforced Plastic (CFRP) laminates is widely used due to its advantages in inspection, replacement and reliability, even though it has disadvantages in stress concentration. It should be designed to have the bearing failure mode because its strength is high and it fails non-catastrophically. It was derived that in the static loading, the critical damage yielding shear matrix crack was kink and the critical condition to the final failure was the appearance of kink in every inner 0° layer. Here it is shown that in the fatigue loading the critical damage that yields shear matrix crack is almost always kink-like damage along the collapse front. Next, the non-elastic elongation of a hole at the maximum load is focused on and its capability is figured out for various stacking sequences. The critical value U_NE,F ^*, which is a non-elastic elongation subtracted by the initial rapid increase depending on the stochastic conditions such as the smoothness of hole surface and the force alignment, is around 35μm and independent of the maximum load and frequency. The critical condition to the final fatigue failure at U_NE,F ^* is roughly the appearance of the kink-like damage in the most of inner 0° layers.