Prediction of creep rupture in unidirectional composite: Creep rupture model with interfacial debonding and its propagation

This paper describes a creep rupture model that takes into account the interfacial debonding and its propagation around broken fibers in unidirectional fiber-reinforced polymers. The interfacial debonding is accompanied by fiber breaks under a longitudinal tensile load, and the interfacial debonding length depends on both the fiber stress at the moment of the fiber breaks and the properties of the interfacial adhesion. In this paper, the interfacial debonding length, its propagation as a function of time, the probability of fiber breaks and an interfacial shear stress are investigated by fragmentation tests with a single glass fiber embedded in each vinylester resin specimen. Subsequently, it was found that a relationship between the fiber strength and the fiber effective length, the length of the debonding length and stress recovery length subtracted from one fiber length, was log linear, and that the larger the fiber stress, the longer was the interfacial debonding length. Next, creep tests were performed to investigate the creep constants of the vinylester resin, and interfacial debonding propagation tests were also performed to identify the interfacial debondingpropagation behavior as a function of time using single fiber composites subjected to constant strains. We modified the creep rupture model by taking into account the interfacial debonding length, which has a time-dependent characteristic, into a conventional Curtin-McLean creep rupture model. It was found that the predicted creep rupture time of the modified model was shorter than that of the conventional model and that there was no threshold creep stress in the modified model unlike in the conventional model because the interfacial debonding propagation makes the prediction creep rupture time lower as time progresses.