Comparison of Energy Dissipation in the Out-of-Plane and In-Plane Fracture of Paper

A comparison of different delamination tests demonstrates that, when the delamination angle increases from 0º, the total delamination work of paper first decreases and then increases. The decreasing phase is probably caused by a decrease in the work done in the outer plastic zone. At larger angles, the increase arises from bending. Delamination at 0º overestimates the true z-directional fracture energy. The smallest energy occurred at about 90 º, apparently giving the closest estimate. They were approximately equal to in-plane fracture energies normalized with the area of fracture process zone and with the number of fibre layers. This suggests that equal amounts of energy per unit fracture surface dissipate in the out-of-plane and in-plane fractures.