LARGE-SCALE BRIDGING IN COMPOSITES - R-CURVES AND BRIDGING LAWS

Large-scale bridging was studied experimentally in a unidirectional ca rbon fibre/epoxy matrix composite material. For intralaminar cracks a significant increase in the crack growth resistance occurred with incr easing crack extension. The increase in the crack growth resistance wa s 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 pr operties when large-scale bridging occurs. The bridging law (the relat ionship between the local crack opening delta and the local bridging t raction a) was measured. The bridging law was found to be independent of specimen geometry. A bridging law can therefore be used as a materi al property in composites with large-scale bridging. The bridging stre ss was related to the crack opening as sigma proportional to delta(-1/ 2). (C) 1998 Published by Elsevier Science Ltd. All rights reserved.