Fatigue crack growth under variable amplitude loading Part II: analytical and numerical investigations.

In part I, the effects of variable amplitude loadings on the fatigue crack growths were illustrated by means of experimental results. Within the scope of part II, systematic analytical and numerical investigations are presented. Using different analytical concepts it can be shown that the lifetime depends both on the concept used and on the loading sequence. Also, the influence of the parameters that must be fitted by experimental data for all analytical prediction models has been investigated. By means of detailed elastic–plastic finite element simulations it becomes obvious that not only the crack opening caused by large plastic deformations subsequent to overloads and block loadings, but also the stress field in the ligament is an indicator for the retardation effect. If the σy-stresses both at maximum and minimum loading are identical with the σy-stress distribution of an appropriate constant amplitude (CA) loading, one can assume that the interaction effect is annihilated. [ABSTRACT FROM AUTHOR]