It has long been recognised that a defect experiencing a state of low constraint shows improved fracture properties when compared to the same defect in a highly constrained state. Fracture test specimens have, therefore, been designed in such a way as to generate a state of high constraint at the crack tip in order to ensure that the properties measured are conservative. Where a defect, in practice, is not highly constrained then using the fracture toughness measured from a standard test piece leads to an overly pessimistic assessment. With the move toward more accurate design and assessment due to the availability of advanced computational tools, it is advantageous to take this excessive conservatism into account. A particular case that is of interest is the effect that constraint has on the onset of upper shelf temperature (OUST). The OUST is typically defined as the intersection of the fracture toughness loci representing the 5% probability of cleavage and the 50% probability of ductile initiation. This paper details a method which can be used to predict the shift in OUST using the toughness scaling method proposed by Anderson and Dodds and extended to account for the influence of constraint on ductile initiation.

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