PSI - Issue 13

Shigeru Hamada et al. / Procedia Structural Integrity 13 (2018) 1026–1031 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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not a source of dislocation, but of stress concentration. The occurrence of this phenomenon is strongly influenced by crystal orientation. Fatigue crack propagation under Mode II loading is likely to occur when a process forms texture, owing to the alignment of crystal orientations during the process. Therefore, this phenomenon can be termed fatigue crack propagation, owing to repetitive fatigue crack initiation. Hereafter this will be termed “damage accumulation type fatigue crack propagation” (DAFCP). The other possible phenomenon is fatigue crack propagation due to the coalescence of intergranular cracks. This arises due to the accumulation of strain in the grain boundary, following which the grain boundary cracks initiate, coalesce, and propagate. This will not be discussed in the study.

(a)

(b)

Fig. 1. Two mechanical approaches for fatigue crack propagation under Mode I loading by using engineering approximation (a) Dislocation mechanics, which is close to the actual phenomenon; (b) Continuous mechanics, by which a quantitative solution can be obtained.

㻲㼍 㼠㼕㼓 㼡㼑㻌㼏㼞㼍㼏㼗

㻹㼕㼏㼞㼛㼙 㼑㼏㼔㼍㼚 㼕㼟㼙

 y

 y

㻹㼛㼐㼑㻌㻵 㼘㼛㼍㼐 㼕㼚 㼓

Dislocation

Slip

 xy

 xy

㻹㼛㼐㼑㻌㻵 㻵 㼘㼛㼍㼐 㼕㼚 㼓

 xy

 xy

Fig. 2. Fatigue crack propagation and its micromechanisms for Mode I and II loadings.