A Study of Brittle Fracture Initiation in Mild Steel

The purpose of this investigation was to study the conditions of brittle-fracture initiation in low-carbon steel. An elastic-plastic stress analysis was developed from which the state of stress along the minimum section of a notched specimen could be determined as a function of the average applied stress and the yield stress. A series of tests on plate-type specimens, with the same notch configuration as that used in the stress analysis, provided experimental values of average fracture stress under various test conditions. Application of the elastic-plastic stress analysis to the experimental results provided a theoretical prediction of the state of stress at the instant location of fracture initation and also an indication of the position of the elastic-plastic boundary at fracture. It was found that the stress condition necessary for brittle fracture initiation, in the mild-steel specimens studied, was achieved when the maximum tensile stress reached a critical value of approximately 246,000 psi. (Author)