1976 Volume 62 Issue 12 Pages 1523-1531
The effect of specimen thickness B on the fracture toughness KC as well as on the shear lip thickness BSL of high strength steels was examined to obtain new models for explaining the thickness dependency of KC, and the influence of tensile properties on the dependency was studied.
The results obtained are as follows.
(1) For each steel, KC increases with the increase of B in a smaller thickness range where slant fractures occur. In the middle thickness range, however, where fractures of a slant-flat mix mode occur, KC decreases with the increase of B, and in a larger thickness range where flat fractures predominate, KC gradually decreases to a constant value (plane strain fracture toughness KIC).
(2) The shear lip thickness BSL decreases with the increase of specimen thickness B in the range of the mix mode fracture.
(3) The new models proposed in this study can express the thickness dependency of KC relatively well.
(4) An approximate relation, BSL/B=αβmc holds between BSL/B and the relative plastic zone size βC (=K2C/Bσ2ys, where σys, is yield strength). The exponent m does not much change with materials (m=0.6-1.0), but the coefficient α is dependent on the work hardening exponent n (α≈0.0016/n1.6).