Stress state and stress‐induced microstructural evolution around the crack tip of G115 steel after dwell‐fatigue crack propagation

Abstract

Many components operate under creep‐fatigue loading causing an increasing need to learn the knowledge about creep‐fatigue crack growth (CFCG). The stress and microstructural evolution around the crack tip of G115 steel after CFCG were investigated. According to the finite element simulations, the variations of equivalent stress and stress triaxiality in the crack tip zone are presented. Furthermore, the evolutions of martensitic laths, dislocations, and precipitates were systematically studied through electron backscatter diffraction and transmission electron microscopy observations. The laths at the crack tip or under a larger hold time are wider than those remote from the crack tip or under a shorter dwell time. Meanwhile, the dislocation densities reduced significantly at the crack tip or under a larger hold time. The different variations of laths' width and dislocation densities resulted from the different stress triaxiality and creep strain. W‐rich Laves and Cu‐rich phases appeared during CFCG. The Laves phase coarsened rapidly because of the stress‐accelerated diffusion.

Interaction analysis between strain concentration and strain localization in cracked body

“…The reason why the authors chose these four lines was to understand the effects of SL on extended lines that are not collinear with the crack. For the crack propagation, the formation and coalescence of voids play an important role and always happen in the zone ahead of the crack tip instead of above the crack face 6,50,51 . Therefore, the effects of plastic strain for the zone above the crack face were not the research target, and the lines were not extended to the element above the crack face.…”

Experimental investigation on creep‐fatigue behaviours of as‐received and service‐exposed turbine blades: Mechanism and life evaluation

“…[5][6][7][8] Creep-fatigue interaction is a typical damage mode of turbine components, and attracts numerous attentions. [17][18][19][20] Wang et al 17 proposed a creep-fatigue life estimation model using the concept of the hysteresis energy density rate. Rai et al 18 experimentally investigated the creep-fatigue deformation micromechanisms of CM 247 DS LC alloy and suggested that the generation of dislocation substructures changed with the dwell times.…”

“…Creep‐fatigue interaction is a typical damage mode of turbine components, and attracts numerous attentions 17–20 . Wang et al 17 proposed a creep‐fatigue life estimation model using the concept of the hysteresis energy density rate.…”