A fracture-mechanics model of the microbond test with interface friction

The microbond test is commonly used to measure the toughness of fiber/matri x interfaces. However, interfacial friction tends to stabilize the crack an d increase the peak load as compared to a friction-free crack with the same interface toughness. Nevertheless, for a constant friction shear stress bo th the interface toughness and friction stress can be approximately determi ned from load vs. crack length or load vs. displacement hysteresis curves ( including energy dissipation, residual displacement or compliance measureme nts). A friction-free crack is used as a reference solution, and friction i s taken into account in the reduced crack-tip fiber load and debonded fiber elongation. When expressed in terms of these two quantities, the energy re lease rate and fiber end displacement are almost independent of the amount of friction. The approximation involved is verified by a finite-element ana lysis. (C) 1999 Elsevier Science Ltd. All rights reserved.