PSI - Issue 13

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

1030

5

㻯㼞㼍㼏㼗 㻌㼓 㼞㼛㼣 㼠㼔 㼙 㼑㼏㼔㼍㼚 㼕㼟㼙

㻲㼍㼠㼕㼓 㼡㼑㻌 㼏㼞㼍㼏㼗 㼙 㼛㼞㼜㼔㼛㼘㼛㼓 㼥

㻰 㼕㼟㼘㼛㼏㼍㼠㼕㼛㼚 㼑㼙 㼕㼟㼟㼕㼛㼚

㻸㼛㼍㼐 㼕㼚㼓

  

Dislocation

㻩

  

Fig. 4. Coarse slip type fatigue crack growth and fatigue crack morphology under Mode II loading.

㻰㼍㼙 㼍㼓 㼑 㼍㼏㼏㼡㼙 㼡 㼘㼍㼠㼕㼛㼚

㻯㼞㼍㼏㼗 㻌㼜 㼞㼛㼜 㼍㼓 㼍㼠㼕㼛㼚 㼙 㼑㼏㼔㼍㼚 㼕㼟㼙

㻲㼍㼠㼕㼓 㼡㼑㻌 㼏㼞㼍㼏㼗 㼙 㼛㼞㼜㼔㼛㼘㼛㼓 㼥

㻸㼛㼍㼐 㼕㼚㼓

  

Damage accumulation unit

Crack initiation

Fig. 5. Damage accumulation type fatigue crack propagation and fatigue crack morphology under Mode II loading.

4. Novel fatigue crack propagation test method under Mode II loading

From the above discussion, we established the following experimental requirements for clarifying the fatigue crack propagation mechanism in RCF.  Pure Mode II load should be achieved. Although there is an experimental method titled “ Mode II loading test ”, it is actually a mixed mode loading test.  There should be direct and successive observation of the propagation behavior. Because the real phenomenon occurs inside the specimen/structural components, direct observation is difficult.  It should be applicable for plastically deformed materials under rolling contact load. The rolling contact-induced plastic strain may be simulated by simple rolling; however, it is not known whether microstructure and damage evolution by repeated rolling contact loading are equivalent to that by rolling. To satisfy these requirements, we developed a novel test method (Hamada et al. 2018). Figure 6 shows the schematics. A thin film few millimeters in size was used as a specimen, so that it can be taken out from an actual machine subjected to plastic working. A sharp notch was introduced using a focused ion beam. Adhering the specimen