On matrix crack saturation in composite laminates

This paper presents a comparative experimental investigation on matrix crack saturation in the constrained laminae of glass-fibre resin composite laminates. Fatigue tests under load and strain control were conducted on [+/- theta/90(3)](S) and [0/ +/- theta(4)/0](T) laminates, respectively. The crack density was periodically measured by using digital image method and optical microscope examination during fatigue tests, to determine crack saturation. It is found that matrix crack saturation occurs in all laminates of different lay-ups under both stress and strain control cyclic loading. The crack density at saturation in the constrained plies is dependent on the cyclic loading type, the off-axis angle of the laminates, as well as the constraining ply. Based on the strain energy release rate, a crack saturation criterion is developed and the experimental findings are qualitatively analysed. (C) 2003 Elsevier Science Ltd. All rights reserved.