Abstract
The workability of wire and rod in upsetting and related processes is dependent on the ductility exhibited by the expanding free surface. From previous measurements of the equatorial strain histories during incremental upsetting of cylinders, linear fracture conditions for a large number of materials of engineering importance have been derived. A simple theoretical explanation of the experimentally observed fracture condition is given. This is done using the concept of a thermo-plastic shear instability criterion. It is shown that one mode of shear instability coincides with the observed straight-line fracture condition.

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