Significance of Cyclic History Dependent Deformation Phenomena of Metals on Fatigue Life Estimation.

摘要

Simple calculations for determining estimated extremes in fatigue life of metals with or without accounting for cycle dependent hardening,softening and mean stress relaxation in fatigue analysis,are presented. These calculations aid in assessing the importance of cyclic deformation properties in cumulative damage procedures. An SAE 1045quenched and tempered steel is considered for illustration. In general cycle dependent deformation phenomena may be important only in intermediate and long life situations. The sensitivity of predicted life to cyclic hardening or softening depends on the degree of hardening or softening a material exhibits,whereas in the case of mean stress relaxation it depends on the shape of the cyclic stress-strain curve or the strain hardening exponent. However the need for a proper accounting of cyclic history,recognized as the 'cycle counting problem'in fatigue literature,is the most important requisite of a cumulative damage analysis. Two alternative approaches of dealing with the cycle counting problem are discussed. (Author)