Characterisation and modelling of the notched tensile fracture of woven quasi-isotropic GFRP laminates

Damage growth and fracture at circular holes in quasi-isotropic laminates, assembled from four layers of woven glass fabric, loaded in tension has been studied. A comprehensive notch-edge damage analysis was performed by a combination of recording tests on video, plan-view photography and a de-ply technique, enabling a layer-by-layer analysis. It was shown that the notch-edge damage initiation and propagation comprised matrix cracking, fracture of the 0° tows, delamination and longitudinal splitting. The tows in the fabric layers oriented at 45° within the damage zone remained intact up to the maximum load in a tensile test. The well-known semi-empirical point-stress and average-stress criteria resulted in accurate notched strength predictions with the average-stress criterion being better than the point-stress criterion. A recently developed critical damage growth model, requiring as input parameters the unnotched strength and fracture toughness of the laminate which were measured from independent experiments, yielded accurate notched strength predictions (to better than 10%), while being very easy to implement. Predicted damage zone lengths from the critical damage growth model generally agreed well with experimental observations.