ABSTRACT
Fatigue involves either stress or strain induced stress reversals. Simple stress controlled loading and unloading tests, such as indirect tensile tests, lead to a creep and fatigue induced accumulation of permanent deformation and are therefore not suitable to determine pure fatigue properties easily. The phenomenological difference between creep and damage related permanent deformation can be demonstrated by simple mechanical models (Parti, 1991). Resting periods between loading impulses as e.g. produced by haversine/ recovery
cycles in the laboratory or by road traffic are considered favorable to healing and heating effects, as it gives time :
• to close and bond microcracks and to mobilize viscoelastic recovery effects, • to internal redistribution of stresses/strains, especially by reducing stress/strain
concentrations, • to reduce local heating and hence to create a more equal temperature
distribution by temperature flow.
