Résumé

The resistance to delamination of unidirectional fibre reinforced laminates increases with crack growth due to large scale bridging. This toughening mechanism, which is reflected by the increasing resistance curves, is subject to size effects. In this work, the influence of the ply thickness on the energy release rate (ERR) in mode I delamination of unidirectional carbon-epoxy laminates is characterized. Three ply thicknesses are considered from thin-ply (0.030 g/m2) to thick-ply (0.150 g/m2). While the ERR at onset of crack propagation do not depend on the ply thickness, the plateau level varies considerably. This effect is attributed to the change of homogeneity of the microstructure, which affects the amount of bridging fibres. Due to the tow spreading procedure used during the production of the prepregs, resin rich regions are present in thick ply laminates, while the fibre distribution is more homogeneous in thin-ply laminates. The heterogeneity of the microstructure increases the probability to have bundles of fibres trapped between the crack faces and eventually leads to higher bridging energy and higher ERR plateau.

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