Abstract
In this investigation, mechanical stress-strain hysteresis, temperature and electrical resistance measurements were performed to characterize the fatigue behavior and to calculate the lifetime of metallic materials under stress-controlled single step and random loading. Single step sequences are periodically inserted in random loading tests to measure the plastic strain amplitude as well as the deformation-induced changes of the temperature and the electrical resistance. These fatigue data are plotted versus the number of cycles in so-called cyclic 'deformation' curves to describe and evaluate the fatigue behavior under random loading, similar as commonly practiced under single step loading. On the basis of Morrow and Basquin equations, which are generalized to be applicable for the applied measuring techniques, a physically based fatigue life calculation "PHYBAL" was developed. This new short-time procedure requires data of only three fatigue tests for a rapid and nevertheless very precise determination of Woehler curves for single step loading or fatigue life curves for random loading, leading to an enormous saving of experimental time and costs.
