Validating the Mechanical Nature of the Test Speicmen Thickness Effect on Fracture Toughness in the Transition Temperature Region

Abstract

This paper considered the test specimen thickness (TST) effect on the fracture toughness of a material Jc, in the transition temperature region, for 3PB (i.e., SE(B) for ASTM standard) specimens. Fracture toughness tests and elastic-plastic finite element analyses (FEA) with non-standard test specimens, on the point that the specimen thickness to width to ratio B/W was varied in the range of 0.25 to 1.5, were conducted. Based on these tests and FEA results, it was demonstrated that Jc showed tendency to saturate to some lower bound for B/W = 1.5. This tendency was similar with that predicted by our previous work, which assumed the TST effect on Jc as an out-of-plane crack-tip constraint issue. Because the TST effect on Jc (such as Jc ∝ B(−1/2)) together with Jc’s bounding nature for large B could not be predicted by the weakest link model but out-of-plane constraint assumption worked, it was concluded that the TST effect is mainly mechanical in nature.