An investigation into the damage development 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. Two quasi isotropic carbon/epoxy laminates, with stacking sequence [45₂/90 ₂/-45₂/02]_S and [45/90/-45/0]_2S were examined. These were selected on the basis that under quasi-static loading they respectively exhibited delamination dominated and fibre dominated failure modes. Specimens were fatigue loaded at 5Hz with various amplitudes to 1E6 cycles or catastrophic failure, which ever occurred first. For both laminates failure occurred by delamination. A number of tests were interrupted at various points as the stiffness dropped with increasing cycles. The interrupted test specimens were inspected using X-ray Computed Tomography (CT) scanning in order to accurately determine a sequence of damage events leading to failure.