Investigation of creep-fatigue crack initiation by using an optimal dual-scale modelling approach

Abstract

In this work, three dual-scale modelling approaches containing sub-modelling approach, coupled modelling approach and full-field crystal plasticity finite element (CPFE) approach are implemented for notched structures under creep-fatigue loading conditions. Based on the comprehensive comparisons, the sub-modelling approach is determined to be an optimal simulation strategy among them. Furthermore, the combined effects of grain orientation and stress concentration on crack initiation are investigated by adopting the sub-modelling approach. Under low stress concentration factor, the most potential positions of crack initiation randomly locate at the root of geometric discontinuities owing to the influence of grain orientation distribution. With the increase in stress concentration factor and decrease in the number of grains at hotspots, the cooperative relation between grain orientation and stress concentration factor for creep-fatigue crack initiation is revealed through a sequence of simulation results, followed by the competitive relation. On this basis, a feature region map is constructed to distinguish the factor-dominated crack initiation. Finally, a case study of turbine disk is provided to illustrate the engineering meanings of the dual-scale modelling approach. The link from scientific problem to engineering application for the crack initiation prediction is bridged by the damage mechanics approach, which is also expected to be promoted in many high-temperature components.