Influence of the Stacking Sequence and Load Direction on the Fatigue Behaviour of Quasi-isotropic Graphite/Peek Laminates

Abstract

Fatigue behaviour of graphite/PEEK quasi-isotropic symmetric laminates, subjected to tension-tension loading with fatigue ratio R = 0·1, has been extensively analysed. Two stacking sequences were considered, i.e. [45/90/–45/0] and [0/45/–45/90] and two load, and specimen, directions 0° and 22·5°. Results reveal no significant differences, in the S-fog N plane, between the two sequences. A relevant different behaviour however is observed varying the load direction. For specimens at 22·5°, data show a decrease in fatigue strength with respect to the 0° direction, that can reach 19% at 100000 cycles. During the tests the hysteresis cycle was continuously recorded and processed to follow damage progression. The final loss of stiffness seems to have no clear relation with the load direction. For the final maximum strain the hypotheses of independence on the number of cycles formulated by some authors was checked.