Stress Intensity Factor Plasticity Correction for Flaws in Stress Concentration Regions
Plasticity corrections to elastically computed stress intensity factors are often included in brittle fracture evaluation procedures. These corrections are based on the existence of a plastic zone in the vicinity of the crack tip. Such a plastic zone correction is included in the flaw evaluation procedure of Appendix A to Section XI of the ASME Boiler and Pressure Vessel Code. Plasticity effects from the results of elastic and elastic-plastic explicit flaw finite element analyses are examined for various size cracks emanating from the root of a notch in a panel and for cracks located at fillet fadii. The results of these caluclations provide conditions under which the crack-tip plastic zone correction based on the Irwin plastic zone size overestimates the plasticity effect for crack-like flaws embedded in stress concentration regions in which the elastically computed stress exceeds the yield strength of the material. A failure assessment diagram (FAD) curve is employed to graphically c haracterize the effect of plasticity on the crack driving force. The Option 1 FAD curve of the Level 3 advanced fracture assessment procedure of British Standard PD 6493:1991, adjusted for stress concentration effects by a term that is a function of the applied load and the ratio of the local radius of curvature at the flaw location to the flaw depth, provides a satisfactory bound to all the FAD curves derived from the explicit flaw finite element calculations. The adjusted FAD curve is a less restrictive plasticity correction than the plastic zone correction of Section XI for flaws embedded in plastic zones at geometric stress concentrators. This enables unnecessary conservatism to be removed from flaw evaluation procedures that utilize plasticity corrections.
- Research Organization:
- Bettis Atomic Power Lab., West Mifflin, PA (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC11-98PN38206
- OSTI ID:
- 755397
- Report Number(s):
- B-T-3288; TRN: AH200038%%348
- Resource Relation:
- Conference: ASME Pressure Vessels and Piping Conference, Seattle, WA (US), 07/23/2000--07/27/2000; Other Information: PBD: 1 Feb 2000
- Country of Publication:
- United States
- Language:
- English
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