Effects superposition under imposed deterioration and simultaneous fatigue in different regimes

The problems of loading superposition of low cycle fatigue, finite cycle fatigue and high cycle fatigue on cracked structure are analyzed. The nonlinear power law behavior of the structure material has been considered. A strength criterion was established for a cracked structure under low cycle fatigue, finite cycle fatigue, and high cycle fatigue loading taking into account the deterioration. On the basis of concept of the specific energy participation and using Basquin’s law and Coffin–Manson’s law, a general relationship of fatigue life was established in the case of superposition of low cycle fatigue, finite cycle fatigue, and high cycle fatigue loadings on a mechanical structure deteriorated due to cracks. The derived relationships depend on the high cycle fatigue and finite cycle fatigue mean stress and on the low cycle fatigue mean strain, as well as on deterioration. Relationships for the deterioration calculation were established. Experimental work was performed for specimens with cracks, made of steel, statically and cyclically loaded. A numerical example shows how the established relationships may be used.