Abstract: There are static and cyclic damages in materials.The static damage is the ratio of plas- tic strain energy due to first applied static load to static toughness of material,and the cyclic damage can be obtained by calculating the ratio of cyclic plastic hysteresis energy to fatigue toughness of material.In calculating the cyclic damage,we have been concerned with influences of yield stress increment(or decrement)caused by cycle-dependent hardening(or softening)of material.In order to simplify the calculating,we assume that the stress-strain curves at cyclic loading all follow hysteresis loops and fatigue toughness of material under different stress ranges can be detennined by cyclic symmetry stress control fatigue tests.In this paper,we have advanced anew fatigue life estimating method under random loading.The new method is reasonable and convenient in engineering application. It is satisfactory in the preliminary experimental verification.

Key words: plastic deformation, static characteristics, fatigue tests, fatigue life, random loads