Effect of Specimen Dimensions on Critical -Value at the Onset of Crack Extension
SourceThis paper presents the experimental results of a test program designed to evaluate the effect of specimen dimensions on the critical J transition curve. These tests were conducted, along with KIc measurements, on four quenched-and-tempered medium strength steels with 15 to 200 mm thick specimens. In the cleavage fracture domain, Jc yielded toughness values that overestimated KIc, especially with the smallest specimens. Although ASTM E 813 requirements were met, the cleavage to ductile tearing transition temperature increased with increasing the J-specimen size. The level of the ductile plateau was found to be strongly dependent on the uncracked ligament length. It is pointed out that JIc measurements may overestimate the plane-strain fracture toughness, the ASTM E 813 size requirements being not restrictive enough.