Extension of Paris Equation & Its Application in the Study of Fatifue Process

Abstract

In 1964 Prof P. C. Paris developed an equation to estimate the fatigue crack-growth rate. It is generally believed that actual growth rate of fatigue crack deviates from Paris Law when crack propagation becomes very fast during the later part of the fatigue Life. But actually it is due to some geometric factors. Experiments on un-notched cylindrical specimens of mild steel (0.23%C) has shown that if the shift in the neutral axis during fatigue crack growth is taken into account and stress is calculated on the basis of this then the corrected form of Paris Equation can be used till the fracture of the specimen. Actually it has been found the fatigue life predicted by theoretical Calculation based on this equation is very close to the experimental values. In this experiment this has been established for specimens tested at five different stress levels.