Practical application of COD measurement in welded assemblies

Measurement of the COD makes it possible to evaluate sensitivity to brittle fracture initiation. This technique is ideal for welded structures, owing to the types of defect likely to affect them, and the magnitude of the residual stresses introduced. Moreover, the COD concept, based on thickness and temperature experiments on materials, enables evaluation of the critical defect size in these structures. However, its application to welded joints encounters certain problems. The presence of fatigue cracks in the molten zone of a welded joint is frequently disturbed by the residual stresses caused by welding. An additional difficulty is created by the problem of stable growth of the crack during the bending test. This discussion covers all these matters and suggests some solutions