Behavior of small cracks under negative stress ratio fatigue loading. (November 2017)

• Record Type: Journal Article
• Authors: Roiko, A.; Solin, J.; Hänninen, H.
• Is Part Of: International journal of fatigue. Volume 104(2017)
• Page Start: 379
• Page End: 388
• Publication Date: 2017-11
• Subjects: Materials -- Fatigue -- Periodicals; Materials -- Fatigue; Periodicals; 620.1122
• DOI: 10.1016/j.ijfatigue.2017.07.006
• Languages: English
• ISSNs: 0142-1123

Abstract

Highlights: Small fatigue cracks, initiate quickly and then grow very slowly. ΔK+ works well to compare small fatigue crack growth rates in the studied steel. Crack arrest ΔK+ or Kmax thresholds are lower with higher compressive loading. Increasing the compressive portion of loading can reinitiate arrested small cracks. The growth rate of small fatigue cracks is increased by up to a factor of 4 for large compressive loads. Abstract: In this paper we analyze growth of small cracks initiated from microscopic notches and loaded near the growth threshold under different stress ratios. The results of in-situ optical measurements during high cycle fatigue testing show that small cracks initiate and grow quickly after which there is a long period of slow growth until the large crack growth threshold is reached. The crack growth rate data from different loading ratios indicates that the positive portion of the stress amplitude or the maximum stress intensity factor can be used to compare crack growth rates. The test data also shows that increasing only the compressive stress portion of the loading will cause an arrested small crack to grow again.