Destructive testing of defective weldments: Fracture mechanics predictions of failure loads and defect criticalities compared with experimental results

Thirty welded test plates containing discrete artificial defects were tested to destruction under controlled four point bending, and the failure loads recorded. The defect parameters, length, height and depth, were measured from the resulting fracture surfaces. Prior to destructive testing, the defective welds had been ultrasonically inspected, in two separate UT programmes, by a number of independent operators. Both actual and predicted defect sizes were used in conjunction with the Design Curve approach of British Standard PD 6493 to calculate failure stresses for each of the test plates. In addition, the Failure Assessment Diagram of the Central Electricity Generating Board (UK) R-6 document was used to establish defect criticality, of both the actual and the predicted defect parameters.

The results obtained indicate that there appeared to be some tolerance in both assessment routes to the significant variability observed in the ultrasonic defect size predictions. However, precise predictions of failure stress levels and defect criticalities are only possible when defects are accurately sized.