Mixed mode (I+II, I+III) fatigue crack growth description in S355/P355NL1 steel

Abstract

Fatigue crack growth models (mostly empirical) are usually constructed using stress intensity factor – ΔK in linear-elastic fracture mechanics. Contrary to the kinetic fatigue fracture diagrams (KFFDs) based on ΔK, Kmax new energy diagrams based on strain energy density parameter ΔH, ΔS* demonstrates no sensitivity to mean stress effect expressed by the stress ratio R. According to the dimensional analysis approach ΔH, ΔS* is replaced by elastic-plastic fracture mechanics parameter based on the energy parameter associated with ΔJ energy parameter range. Hence, the main goal of this paper is the application of the new averaged strain energy density parameter ΔS* based on hysteresis loop curves for cracked components under uniaxial as well as multiaxial stress state. The presented approach assumes that the fatigue crack growth increment in the elastic-plastic range is caused by the combination of the maximum value of the energy parameter and its positive part of the range in each cycle of loading. The usefulness and invariance of this parameter have been confirmed in many works.