Statistical analysis of multiple fracture in 0°/90°/0° glass fibre/epoxy resin laminates

Measurements of the distributions of crack spacings developed in the 90° ply of 0°/90°/0° glass fibre/epoxy resin laminates under tensile loading show that the ply has a variable strength. As a consequence the strain at which cracking begins is very dependent on the specimen length. The observed distributions of crack spacing are not consistent with the assumption of a uniform strength for the 90° ply. A statistical model provides a good description of the cracking behaviour particularly when the cracks are widely spaced. Magnification of the stress in the matrix between the relatively stiff glass fibres leads to debonding which is observed as a reversible “stress-whitening.” The distributions reveal a lower probability of crack formation in the under-stressed region close to the existing cracks and provide estimates of the size of this region. The method of analysis can be applied to many systems which exhibit multiple fracture.