Statically admissible stress fields consisting of regions of constant stress in a state of incipient plastic flow separated by stress discontinuities form a powerful tool for obtaining lower bound solutions to problems in plane plastic flow.
The properties of discontinuities which meet on an axis of symmetry are investigated and it is shown that solutions exist for ‘reflections’ of the discontinuity at the axis at angles of π/4 and 3π/4 as well as the angle π/2 hitherto assumed to be the only solution.
The results are used to obtain a lower bound solution for plane-strain extrusion with reduction ratios less than 3:1.
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