Tensile and shear instabilities in tensile tests on rods and sheets

Abstract

Results of researchers in the fields of room-temperature and cryogenic tensile testing are reviewed with particular reference to metallographic details. This review leads to the proposition of a mechanism of shear localization in bands in both rod and sheet tensile specimens. This mechanism is thermoplastic shear instability. The concept of ‘tensile instability’ is not precise. It is shown that tensile instability is a result of a blend of thermoplastic and geometrical softening. This has been confirmed in the case of sheets and thermoplastic shear instability seems to be the more likely cause of the initiation of localized necking. Based on this, some new approaches and explanations of the mechanism of ductile fracture in a rod tensile specimen are proposed.

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