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Title: Assessment of Cracks in Stress Concentration Regions with Localized Plastic Zones

Abstract

Marty brittle fracture evaluation procedures include plasticity corrections to elastically computed stress intensity factors. These corrections, which are based on the existence of a plastic zone in the vicinity of the crack tip, can overestimate the plasticity effect for a crack embedded in a stress concentration region in which the elastically computed stress exceeds the yield strength of the material in a localized zone. The interactions between the crack, which acts to relieve the high stresses driving the crack, plasticity effects in the stress concentration region, and the nature and source of the loading are examined by formulating explicit flaw finite element models for a crack emanating from the root of a notch located in a panel subject to an applied tensile stress. The results of these calculations provide conditions under which a crack-tip plasticity correction based on the Irwin plastic zone size overestimates the plasticity effect. A failure assessment diagram (FAD) curve is used to characterize the effect of plasticity on the crack driving force and to define a less restrictive plasticity correction for cracks at notch roots when load-controlled boundary conditions are imposed. The explicit flaw finite element results also demonstrate that stress intensity factors associated with load-controlledmore » boundary conditions, such as those inherent in the ASME Boiler and Pressure Vessel Code as well as in most handbooks of stress intensity factors, can be much higher than those associated with displacement-controlled conditions, such as those that produce residual or thermal stresses. Under certain conditions, the inclusion of plasticity effects for cracks loaded by displacement-controlled boundary conditions reduces the crack driving force thus justifying the elimination of a plasticity correction for such loadings. The results of this study form the basis for removing unnecessary conservatism from flaw evaluation procedures that utilize plasticity corrections.« less

Authors:
Publication Date:
Research Org.:
Bettis Atomic Power Laboratory (US)
Sponsoring Org.:
Bettis Atomic Power Laboratory (US)
OSTI Identifier:
8002
Report Number(s):
WAPD-T-3225
TRN: AH200116%%154
DOE Contract Number:  
AC11-93PN38195
Resource Type:
Conference
Resource Relation:
Conference: ASME Pressure Vessels and Piping Conference, Boston, MA (US), 08/01/1999--08/05/1999; Other Information: PBD: 25 Nov 1998
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; BOUNDARY CONDITIONS; DEFECTS; MANUALS; PLASTICS; PRESSURE VESSELS; STRESS INTENSITY FACTORS; THERMAL STRESSES; YIELD STRENGTH

Citation Formats

Friedman, E. Assessment of Cracks in Stress Concentration Regions with Localized Plastic Zones. United States: N. p., 1998. Web.
Friedman, E. Assessment of Cracks in Stress Concentration Regions with Localized Plastic Zones. United States.
Friedman, E. 1998. "Assessment of Cracks in Stress Concentration Regions with Localized Plastic Zones". United States. https://www.osti.gov/servlets/purl/8002.
@article{osti_8002,
title = {Assessment of Cracks in Stress Concentration Regions with Localized Plastic Zones},
author = {Friedman, E},
abstractNote = {Marty brittle fracture evaluation procedures include plasticity corrections to elastically computed stress intensity factors. These corrections, which are based on the existence of a plastic zone in the vicinity of the crack tip, can overestimate the plasticity effect for a crack embedded in a stress concentration region in which the elastically computed stress exceeds the yield strength of the material in a localized zone. The interactions between the crack, which acts to relieve the high stresses driving the crack, plasticity effects in the stress concentration region, and the nature and source of the loading are examined by formulating explicit flaw finite element models for a crack emanating from the root of a notch located in a panel subject to an applied tensile stress. The results of these calculations provide conditions under which a crack-tip plasticity correction based on the Irwin plastic zone size overestimates the plasticity effect. A failure assessment diagram (FAD) curve is used to characterize the effect of plasticity on the crack driving force and to define a less restrictive plasticity correction for cracks at notch roots when load-controlled boundary conditions are imposed. The explicit flaw finite element results also demonstrate that stress intensity factors associated with load-controlled boundary conditions, such as those inherent in the ASME Boiler and Pressure Vessel Code as well as in most handbooks of stress intensity factors, can be much higher than those associated with displacement-controlled conditions, such as those that produce residual or thermal stresses. Under certain conditions, the inclusion of plasticity effects for cracks loaded by displacement-controlled boundary conditions reduces the crack driving force thus justifying the elimination of a plasticity correction for such loadings. The results of this study form the basis for removing unnecessary conservatism from flaw evaluation procedures that utilize plasticity corrections.},
doi = {},
url = {https://www.osti.gov/biblio/8002}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Nov 25 00:00:00 EST 1998},
month = {Wed Nov 25 00:00:00 EST 1998}
}

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