Fracture toughness results are measured in the transition region for an ASTM A471 Ni-Cr-Mo-V steel on two specimen sizes 1T compact tension (CT) and 4T-CT. The results are typical for steels in the transition in that the smaller specimen toughness values are greater than the larger specimen results. Two explanations are given for this behavior. One explanation, based on loss of constraint, suggests that small specimens cannot be used to characterize the toughness of a large structure in the transition region. A second explanation, based on a statistical model, suggests that small specimen results when properly analyzed can be used to characterize the toughness of large structures.

The results of these tests and others support the statistical model as the proper explanation for the observed difference in toughness between small and large specimens in the transition. The model gives a method for analyzing small specimen results to properly predict the toughness of a large structure.