On micro‐defect induced cracking in very high cycle fatigue regime

It is known that fine granular area morphology is often formed around interior micro‐defect in the case of very high cycle fatigue failure of high strength steel. The mechanism of “fragmentation of martensitic laths and formation of dislocation cells” (Zhu's model), which revealed a microstructure‐dependent crack initiation and early growth for micro‐defect induced internal fatigue cracking, was discussed in several lathy martensitic or similar steels, verified under environmental fatigue, and applicable to white etching crack in rotating contact fatigue. A machine learning‐ Z parameter integrated approach was developed for fatigue life, which is promising for design against fatigue of engineering structures for long life.