A SINGLE EXPRESSION FORMULA FOR INVERTING STRAIN‐LIFE AND STRESS‐STRAIN RELATIONSHIPS

Abstract

Abstract Starting with the basic fatigue life formula Δε/Δε T = ( N f / N T ) b + ( N f / N T ) c an inversion formula is derived in the form N f / N T = [(Δε/Δε T ) z/b + (Δε/Δε T ) z/c ] 1/ z where z is a function of strain range and the ratio c/b. The inversion formula is valid over the entire life range of engineering interest for all materials examined. Conformity between the two equations is extremely close, suitable for all engineering problems. The approach used to invert the life relation is also suitable for the inversion of other formulas involving the sum of two power‐law terms.