Unstable ductile fracture in SUS-304 stainless steel under impact loading condition

For the assurance of the integrity of nuclear piping systems in the presence of stress corrosion crackings, it is necessary to make clear of the margin of safety against burst type failure emanating from the cracks. Even in ductile materials - such as type 304 stainless steel-fast fracture might occur as a result of tearing instability under the severest loading conditions. In this report, unstable crack propagation behavior of 304 steel under impact tensile loading is estimated analytically and the results are compared with the experimental data from centre cracked specimens loaded by a spring with high compliance. Estimated values of critical impact load (Pc) causing the unstable fracture are practically 10% lower than the experimental values. For these impact loads, the crack velocity (a) is estimated as higher value than the experimental one. In addition, the influence of the compliance of tensile spring on the impact load as well as the crack velocity are discussed. As a result, it is suggested that the unstable fracture by impact load might take place under the loading conditions in high compliance. (author)