Strain Rate Effects on Fracture Toughness of Ship Plate Steels

Abstract

Full thickness fracture toughness of conventional ship plate grades, including modern high-strength steels, was determined at loading rates representing quasi-static, intermediate, and impact conditions. For testing at impact strain rates (ε̇ = 5 s−1 ), customized equipment was designed and developed for a drop tower. It was shown from the CTOD transition temperature curves that the transition temperature increase from quasi-static to intermediate rate (a three-order rate increase) is much greater than the increase from intermediate to impact (a two-order rate increase). Comparison of the dynamic CTOD, CVN, and NDTT indicated that the correlation between the CVN and 0.1-mm dynamic CTOD transition temperature does not hold for the TMCP steels, for which the CVN transition temperature is much lower. By contrast, the results display a very good correlation between the NDTT and 0.1-mm dynamic CTOD transition temperature for all of the steels tested in this program.