The Initiation of Yielding and Brittle Fracture in Annealed Mild Steel

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The initiation of brittle fracture and the transition between ductile and brittle behavior of an annealed mild steel has been investigated. A theoretical and experimental investigation has been made on notched tensile specimens to determine the state of stress beneath a notch which governs the initiation of a brittle fracture. The experimental investigation was conducted for constant rates of stress application of from [...] to [...] [...] sec at temperatures of -110[degrees] F (-79 [degrees] C) and -200[degrees] F (-129[degrees] C). The stress analysis of the notched specimen includes the effect of limited plastic deformation known to precede brittle fracture. The true tensile stress at the position and instant of initiation of brittle fracture in the notched tensile specimens is determined from the experimental results, a knowledge of the yielding behavior of the material, and the elastic-plastic stress analysis. In this manner it is shown that brittle fracture occurs when a critical value of the maximum tensile stress is attained. This critical value of the tensile stress is found to be constant, independent of rate and temperature, and is shown to occur at the elastic-plastic boundary beneath the root of the notch. The information gained from the investigation of the initiation of brittle fracture in notched tensile specimens is applied to the prediction of the transition temperature in the case of the Izod impact test. The prediction is checked by experiment and the agreement is found to be good