An investigation into the damage development and residual strengths of open-hole specimens in fatigue

An extensive experimental program was carried out to investigate and understand the sequence of damage development throughout the life of open-hole composite laminates loaded in tension tension fatigue. Quasi-isotropic carbon/epoxy laminates, with stacking sequence [45(2)/90(2)/-45(2)/0(2)](s), [45/90/-45/0](2s) and [45/90/-45/0](4s) were examined. These were selected on the basis that under quasi-static loading the [45(2)/90(2)/-45(2)/0(2)](s) configuration exhibited a delamination dominated mode of failure whilst the [45/90/-45/0](2s) and [45/90/-45/0](4s) configurations showed a fibre dominated failure mode, previously described as "pull-out" and "brittle" respectively. Specimens were fatigue loaded to 1 x 10(6) cycles or catastrophic failure, which ever occurred first. A number of tests were interrupted at various points as the stiffness dropped with increasing cycles, which were inspected using X-ray computed tomography (CT) scanning. A static residual strength program was carried out for run-out specimens of each configuration. (C) 2014 Elsevier Ltd. All rights reserved.