MODE-I DELAMINATION OF ANGLE-PLY EPOXY-GLASS-FIBER LAMINATES EXHIBITING PERMANENT DEFORMATION DURING FRACTURE

An analytical method is described for calculating the mode I fracture toughness of angle-ply composites showing permanent deformation during fracture. This is based on the energy conservation principle and assumes a knowledge of the stress/strain behaviour of the material. The presence of both geometric and material iron-linearities is taken into account. The analysis is verified by comparing the calculated fracture toughness with that estimated from the area under the loading-unloading diagrams. The accuracy of the analysis is further confirmed by the agreement between calculated and experimental crack lengths. The fracture toughness data are also compared with results calculated assuming a linear-elastic and linear-elastic/perfectly-plastic behaviour. Surprisingly good agreement is rioted with the uncorrected form of the linear elastic 'displacement' method whereas the linear-elastic/perfectly-plastic analysis gives lower toughness values.