Application of an inclined-strip-yield crack tip plasticity model to predict constant amplitude fatigue crack growth

Abstract

A mathematical model for fatigue crack growth under arbitrarily varying cyclic loads based on the inclined-strip-yield superdislocation representation of crack tip plasticity was initiated in previous work. The results showed promise, but also exhibited some deficiencies. Steps to improve the general model using a heuristic model (in which the superdislocation pairs representing the residual plasticity left behind by a crack growing under constant amplitude loading are lumped into one aggregate pair) are described in this paper. It is shown that this simple model matches the main features of experimental observations on fatigue crack growth. While pointing the way to developing a practical model to treat spectrum loading, the results also offer some potentially valuable insights into the analysis of plasticity-enhanced fatigue crack growth. Of most significance, the results suggest that the compressive stress acting at a crack tip due to residual plasticity may be inseparably linked with crack closure. The generality of the model is also demonstrated by applications to biaxial and crack line loading conditions.