Mode II fatigue delamination of carbon/epoxy laminates using the end-notched flexure test

The fatigue delamination behaviour of carbon/epoxy laminates was investigated through end-notched flexure tests carried out under displacement control. Fatigue tests were conducted at different stress ratios from pre-cracks generated in initial quasi-static tests, which provided fracture toughness values. Crack propagation rates were obtained by a new approach that employed the effective crack method and considered propagation increments of small strain-energy release rate variation. The present results were found to give a more realistic view of the fatigue delamination behaviour by taking either a recently defined strain-energy release rate range or the stress intensity factor range as the main fatigue driving parameter. The analysis took into account the typical power law fits, the influence of the stress ratio and the indication of a possible fatigue threshold. Finally, quasi-static tests conducted from the fatigue pre-crack showed significantly lower initiation critical strain-energy release rates than the ones previously measured.