THE EFFECT OF TORSIONAL PLESTRAIN ON THE EMBRITTLEMENT OF MILD STEEL.

The paper presents the results of a series of tests on notched specimens made of low-carbon DIN 37 Steel, which were torsionally prestrained by different amounts at their plain or notched state and then tested in tension to failure. These tests showed the deleterious influence of pretwisting on the exhaustion of ductility of the metal. It was shown that the most effective mode for exhausting the ductility of the metal was achieved when pretwisted bars were sharpy notched and twisted, before fracturing in tension. Genuine brittle fractures occurring at a nominal stress lower than the virgin yield strength of the material were consistently produced in this manner. A series of plain torsion bars submitted to severe twisting, followed by a gradual reverse torsion, showed that the failure stresses of the subsequently sliced tension specimens passed through consecutive relative maxima and minima before reaching a maximum failure stress corresponding to an untwisting angle equal to the initial twisting. All fractures in these specimens were high stress failures. Author