SIMPLE APPROXIMATIONS FOR BRIDGED CRACKS IN FIBROUS COMPOSITES

Analytical functions approximating the ratio of the net and the applied stress intensity factors are presented for bridged cracks in fibrous composites. The approximations summarize extensive, accurate numerical calculations for mode I matrix cracks growing in specimens of several common shapes under uniform remote loading. The bridging tractions are assumed to be related to the crack opening displacement by laws appropriate to unidirectional fibers coupled to the matrix by friction. The same approximating functions also represent the ratio of the applied and net stress intensity factor ranges in cyclic loading. The application of the functions to the analysis of monotonic and fatigue crack growth data is illustrated. Consideration of the "bridging length scale" concept reveals the kinds of data required for accurately determining relevant material constants and for testing the validity of the modelling assumptions.