CRACK BRIDGING MODELS FOR FIBER COMPOSITES WITH SLIP-DEPENDENT INTERFACES

A THEORETICAL STUDY is made of the role of slip-dependent interfaces in fracture of fiber reinforced composites. The fiber-matrix interface is characterized by the interfacial sliding stress tau which is a function of the position in the sliding zone owing to asperity wear and damage to fiber coatings. Three interface models are proposed to correlate tau with the interfacial sliding displacement DELTA: (1) tau linearly increases with DELTA; (2) tau linearly decreases with DELTA; and (3) tau exponentially decreases with DELTA. Crack bridging traction laws are derived based on a fiber pull-out analysis coupled with the interface models. Systematic calculations are carried out for the stress distribution in the bridging zone and crack tip stress intensity using the linear hardening interface model. It is found that slip-dependent interface properties may have a strong effect on fiber fracture, while the effect on matrix cracking is relatively small. It is also found that the influence of interface damage is coupled with the applied load: the larger the applied load, the stronger the effect. The implications of these findings for fatigue cracking of fiber composites are briefly discussed.