Large-scale bridging in composites: R-curves and bridging laws

Large-scale bridging was studied experimentally in a unidirectional carbon fibre/epoxy matrix composite material. For intralaminar cracks a significant increase in the crack growth resistance occurred with increasing crack extension. The increase in the crack growth resistance was attributed to fibre cross-over bridging. The R-curve behaviour, i.e. the relationship between crack growth resistance and crack extension depended on specimen geometry. Therefore, R-curves are not material properties when large-scale bridging occurs. The bridging law (the relationship between the local crack opening delta and the local bridging traction a) was measured. The bridging law was found to be independent of specimen geometry. A bridging law can therefore be used as a material property in composites with large-scale bridging. The bridging stress was related to the crack opening as sigma proportional to delta(-1/2). (C) 1998 Published by Elsevier Science Ltd. All rights reserved.