Effect of specimen thickness on fracture toughness

Abstract The variation of fracture toughness with specimen thickness for Comsleel En25 compact tension specimens ranging in thickness from 4 mm to 25 mm and tempered from the asquenched state to 600°C is predicted reasonably well using the models proposed by Bluhm Proc. ASTM61, 1324 (1961) and by Hahn etal. Met. Trans. 5, 475 (1974). Both models made use of data from two specimens of any thicknesses in the mixed mode region. The fit of the models suggested by Krafft etal. Proc. Crack Propagation Symp. p. 8, Cranfield (1961) and Tetelman etal. Fracture of Structural Materials, Wiley, New York (1967), was however less accurate. For Krafft's model, the discrepancy was attributed to the difficulty in determining an accurate G cmax ,value for thin specimens as a result of buckling. Tetelman's model implied the assumption that formation of shear lip was a surface phenomenon rather than one formed by a volume sensitive mechanism. This assumption did not appear reasonable for the material used in the investigation.