Notch-Ductility Transition of Structural Steels of Various Yield Strengths

The notch-ductility transition of six structural steels, A36, ABS-Class C, A302-Grade B, HY-80, A517-Grade F, and HY-130, ranging in yield strength from 36 to 137 ksi, was studied with the use of 5/8 and 1 in. dynamic-tear (DT) test specimens. The results were compared with previously published data for V-notch and fatigue-cracked Charpy tests and dynamic fracture-toughness (K_ID) tests. Energy, lateral-contraction, and fracture-toughness values were compared. The results of this study showed that the full-shear upper energy shelves in the Charpy V-notch and DT specimens are the products of constant average plastic energy densities for each steel and the plastic volume estimates for the fracture of the different specimens. The transition from ductile to brittle fracture behavior is essentially the same in the fatigue-cracked Charpy and DT specimens since, for each steel, the same lateral contraction was measured in each specimen broken at a given temperature. This lateral contraction increased exponentially with temperature until a full-thickness shear fracture developed. However, the maximum lateral contraction increased with increased test-specimen thickness, suggesting that the K_c values corresponding to full-shear fracture should also increase with thickness. Using the proportionality found between the lateral contraction and the values of K$ID2$/σ_YDE for the brittle-fracture behavior of these steels, the K_c values are estimated to be as much as 4.5 times greater than the K_Ic values at the same temperatures. In general, the notch-ductility transition can best be quantitatively characterized by the lateral contraction through K_ID and K_c values, whereas upper shelf energies are related by constant plastic energy densities and plastic volumes which develop during fracture.