This paper describes the outcome of a fracture study to ascertain the benefits of using modern three dimensional finite element techniques. The defects considered are postulated to be present at the root of a threaded fastener. The defects are explicitly modelled using three dimensional finite element analysis to extract the relevant fracture parameters.

A large number of thumbnail defects of varying size and aspect ratio have been incorporated into the root of the first engaged thread of studs typically used in pressure vessels. Stress intensity factors at the defect surface and depth locations have been extracted for a number of thermal transient events using a domain integration technique within the general finite element code ANSYS.

The above stress intensity factors were then used to generate fracture calculations using an R6 based procedure [1] for:

• Toughness-based fracture margins for each defect modelled;

• Critical defect size;

• Comparisons with a fully extended defect.

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