The influence of debonding damage on fracture toughness and crack-tip field in glass-particle-reinforced Nylon 66 composites

This paper deals with the influence of the debonding damage between particl es and matrix on fracture toughness and crack-tip field of particle-reinfor ced composites. Tensile strength and fracture toughness were examined on se ven kinds of glass-particle-reinforced Nylon 66 composites in which the vol ume fraction of glass particles and the interface treatment between particl es and matrix were changed. Although the main damage mode is the debonding damage between particles and matrix in both interface-treated and untreated composites, in the interface-treated composite the debonding damage is har d to occur because of high interfacial strength. The interface-treated comp osites are superior in tensile strength, and inferior in fracture toughness to the interface-untreated composite. In order to explain the influence of the debonding damage on the fracture toughness, numerical analysis of a cr ack-tip field was carried out on both composites by using a finite-element method which was developed on the basis of an incremental damage theory of particle-reinforced composites. The damage development around a crack-tip d epends on the interfacial strength between particle and matrix and the part icle volume fraction. It is found that the debonding damage reduces the str ess level around the crack-tip and acts as the toughening mechanism. The me chanical performance of particle-reinforced composites is obtained as the r esults of the competitive effects of the intact hard particles and the debo nding damage. (C) 2001 Elsevier Science Ltd. All rights reserved.