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An engineering procedure for assessing the integrity of flawed structures is presented. The procedure uses results given in a plastic fracture handbook developed by General Electric in the format of the Central Electricity Generating Board of the United Kingdom R-6 failure assessment diagram.
The failure assessment diagram recognizes both brittle fracture and net section collapse of the flawed structure. It is a safety/failure plane defined by the stress-intensity factor/fracture toughness ratio (Kr) as the ordinate and the applied stress/net section plastic collapse stress ratio (Sr) as the abscissa. For a particular stress level and defect size, the coordinates (Sr, Kr) can be easily calculated. If the assessment point lies inside the failure assessment curve, the structure is safe. The distance of the assessment point from the curve is a direct measure of the margin of safety of the assessed structure.
The procedure can handle ductile tearing by redefining the failure assessment curve as the boundary between stable and unstable crack growth. Application of this approach to 2024-T351 aluminum center-cracked panels using plane-stress JR resistance curves developed from compact specimens has given predictions of maximum load to within 2% of experimental values.
An additional example problem of a cracked pressure vessel is included which demonstrates the applicability of this procedure to real structures. Lastly, limitations of the deformation plasticity failure assessment diagram are discussed.
deformation plasticity failure assessment diagram, fracture mechanics, tearing instability, stable crack growth, J-R curves, plasticity, elastic-plastic fracture
Technical advisor, Structural Mechanics, Babcock & Wilcox, Research and Development Division, Alliance, OH