Effect of interaction of embedded crack and free surface on remaining fatigue life

Genshichiro Katsumata; Valéry Lacroix; Yinsheng Li; Genshichiro Katsumata; Valéry Lacroix; Yinsheng Li

doi:10.3934/matersci.2016.4.1748

AIMS Materials Science

2016, Volume 3, Issue 4: 1748-1758. doi: 10.3934/matersci.2016.4.1748

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Research article Special Issues

Effect of interaction of embedded crack and free surface on remaining fatigue life

1.
Mizuho Information & Research Institute, 2-3 Kanda-Nishikicho, Chiyoda-ku, Tokyo 101-8443, Japan
2.
Tractebel (ENGIE), Avenue Ariane 7, 1200 Brussels, Belgium
3.
Nuclear Safety Research Center, Japan Atomic Energy Agency, 2-4 Shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan

Received: 29 September 2016 Accepted: 23 November 2016 Published: 05 December 2016

Embedded crack located near free surface of a component interacts with the free surface. When the distance between the free surface and the embedded crack is short, stress at the crack tip ligament is higher than that at the other area of the cracked section. It can be easily expected that fatigue crack growth is fast, when the embedded crack locates near the free surface. To avoid catastrophic failures caused by fast fatigue crack growth at the crack tip ligament, fitness-for-service (FFS) codes provide crack-to-surface proximity rules. The proximity rules are used to determine whether the cracks should be treated as embedded cracks as-is, or transformed to surface cracks. Although the concepts of the proximity rules are the same, the specific criteria and the rules to transform embedded cracks into surface cracks differ amongst FFS codes. This paper focuses on the interaction between an embedded crack and a free surface of a component as well as on its effects on the remaining fatigue lives of embedded cracks using the proximity rules provided by the FFS codes. It is shown that the remaining fatigue lives for the embedded cracks strongly depend on the crack aspect ratio and location from the component free surface. In addition, it can be said that the proximity criteria defined by the API and RSE-M codes give overly conservative remaining lives. On the contrary, the WES and AME codes always give long remaining lives and non-conservative estimations. When the crack aspect ratio is small, ASME code gives non-conservative estimation.
- embedded crack,
- fatigue crack,
- stress intensity factor interaction,
- fitness-for-service,
- proximity rule,
- remaining fatigue life
Citation: Genshichiro Katsumata, Valéry Lacroix, Yinsheng Li. Effect of interaction of embedded crack and free surface on remaining fatigue life[J]. AIMS Materials Science, 2016, 3(4): 1748-1758. doi: 10.3934/matersci.2016.4.1748

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Abstract

Embedded crack located near free surface of a component interacts with the free surface. When the distance between the free surface and the embedded crack is short, stress at the crack tip ligament is higher than that at the other area of the cracked section. It can be easily expected that fatigue crack growth is fast, when the embedded crack locates near the free surface. To avoid catastrophic failures caused by fast fatigue crack growth at the crack tip ligament, fitness-for-service (FFS) codes provide crack-to-surface proximity rules. The proximity rules are used to determine whether the cracks should be treated as embedded cracks as-is, or transformed to surface cracks. Although the concepts of the proximity rules are the same, the specific criteria and the rules to transform embedded cracks into surface cracks differ amongst FFS codes. This paper focuses on the interaction between an embedded crack and a free surface of a component as well as on its effects on the remaining fatigue lives of embedded cracks using the proximity rules provided by the FFS codes. It is shown that the remaining fatigue lives for the embedded cracks strongly depend on the crack aspect ratio and location from the component free surface. In addition, it can be said that the proximity criteria defined by the API and RSE-M codes give overly conservative remaining lives. On the contrary, the WES and AME codes always give long remaining lives and non-conservative estimations. When the crack aspect ratio is small, ASME code gives non-conservative estimation.

References

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