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TWI Industrial Member Report Summary 349/1987
By T G Davey
Background
A number of procedures are now available for assessing whether defects in a structure can be left in place or whether repair is required. These must be relatively simple, widely applicable and yield safe (conservative) answers. However, excessive conservatism carries the penalty of unnecessary repair. The two most common, simple methods, BS PD 6493 and the CEGB R6 Revision 2 procedure, assess the risk of failure by fracture and by plastic collapse (excessive yielding) in separate calculations. The plastic collapse calculation methods of both procedures seem likely to give excessive conservatism in certain situations.
The degrees of conservatism of plastic collapse calculations can be checked by comparison with available experimental data for surface breaking defects. This report presents the first published plastic collapse measurements for buried defects, and compares them with the predictions of PD 6493, R6, a modified version of these two suggested by Willoughby, and a simple net section stress approach.