Crack Initiation and Propagation in Model Cord-Rubber Composites

The present study suggests that the development of penny-shaped cracks at cord ends is the first stage of fatigue failure of cord-rubber composites. An approximate theory for calculating the strain-energy release rate (tearing energy) for the propagation of penny-shaped cracks and predicting the life of model composites has been outlined. The basic premise of this theory is that the rate of propagation of these penny-shaped cracks is governed by the usual crack-growth characteristics of rubber vulcanizates customarily determined using simple test pieces such as the pure-shear test piece. Fatigue studies on two model composites show experiment and theory to be in semiquantitative agreement. Breidenbach and Lake have already established the relationship between the crack-growth characteristics of the rubber material to interply crack propagation, a later stage in the fatigue failure of cord-rubber composites. Therefore, it is clear that the crack-growth characteristics are an important screening criterion for compound development aimed at improving the life of cord-rubber composites.