Constraint-based assessment of fracture in welded components

A toughness correction method, developed as ISO 27306, specifies an equivalent crack tip opening displacement (CTOD) ratio, β, for the correction of CTOD toughness for constraint loss in structural components. Using β, the standard fracture toughness specimen and structural components are linked at the same level of the Weibull stress. This paper applies the IST method to the fracture assessment of welded components. Effects of the strength mismatch and residual stress in welds on β are implemented into the toughness correction. The strength mismatch does not have an influence on β, provided that the strength mismatch between the weld and base metals is in the range from 0.9 to 1.2. On the other hand, residual stress exerts a large influence at a low CTOD level below full yielding: β is elevated by the tensile residual stress. It is shown on the failure assessment diagram that the CTOD toughness correction with β eliminates the excessive conservatism often found in the conventional approach and leads to accurate fracture assessments of welded components.