Study on Flaw to Surface Proximity Rule for Transforming Subsurface Flaws to Surface Flaws Based on Fatigue Crack Growth Experiments

Abstract

If a subsurface flaw is located very near a component surface, the subsurface flaw is categorized as a surface flaw. The boundary of the subsurface and surface flaws is required for flaw evaluation. The subsurface flaw is transformed to a surface flaw in accordance with a flawtosurface proximity rule. The recharacterization process from subsurface to surface flaw is adopted in all fitnessforservice (FFS) codes. However, the specific criteria of the recharacterizations are different among the FFS codes. Cyclic tensile experiment was conducted on a carbon steel flat plate with a subsurface flaw at ambient temperature. The objective of the paper is to compare the experiment and calculation of fatigue crack growth behavior for a subsurface flaw and the transformed surface flaw, and to check the validity of the flawtosurface proximity rule defined by ASME Code Section XI, JSME S NA1 Code and other codes.