Mixed mode (I + II, I + III) fatigue crack growth rate description in P355NL1 and 18G2A steel using new energy parameter based on J-integral approach

Abstract

In this paper, the problem of fatigue crack growth description under mixed mode loading condition is discussed. A new ΔS* crack driving force is proposed for mixed-mode loading conditions. For experimental verification, two types of low-carbon steels were used (P355NL1 and 18G2A /EU S355/). Mixed mode (I + II) fatigue crack growth rate experiment performed for R = 0.05 and R = 0.5 confirmed the usefulness of ΔS* parameter as a crack driving force. The similar effect was observed in the case of 18G2A (S355) steel and mixed mode (I + III) experiment for R = 0, −0.5, −1. On the contrary to the force factor ΔK or energy parameter ΔJ, the ΔS* approach allows to describe the kinetics of fatigue crack growth independently from stress ratio R. Based on experimental data it is worth to note that the usefulness of mentioned parameter can be reflected in further mathematical models of fatigue crack growth for both constant and variable amplitude loading conditions.