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Say we had a material that was rigid perfectly plastic, with a stress-strain characteristic as shown:

enter image description here

Say that we are drawing this material through two dies, something like this: enter image description here

What would happen if the drawing stress applied were greater than the yield stress?

Of course this is an idealisation, and with a real material, if the stress was raised enough, the material would become plastic and then eventually fail.

However, what would happen with a perfectly plastic material?

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    $\begingroup$ Does a perfectly plastic material have a yield stress? Wouldn't that be contradictory? $\endgroup$
    – fred_dot_u
    Apr 11, 2022 at 14:24
  • $\begingroup$ Well the way I interpreted the stress strain curve was - it's rigid till the yield stress is reached (i.e. no strain) and then once yield stress is reached, it is perfectly plastic. How would you describe a rigid perfectly plastic material? $\endgroup$
    – VJ123
    Apr 11, 2022 at 14:28
  • $\begingroup$ I think he is trying to say elastic, not plastic. $\endgroup$ Apr 11, 2022 at 14:51
  • $\begingroup$ perfectly plastic means it doesn't fail, it just stretches. $\endgroup$
    – Tiger Guy
    Apr 11, 2022 at 15:31
  • $\begingroup$ F=ma. If the applied force exceeds the resisting forces, the piece accelerates. $\endgroup$
    – JohnHoltz
    Apr 11, 2022 at 16:44

1 Answer 1

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I am trying to see what you try to say.

If the rate of drawing (say by creating a vacuum) is not such that it will rip the material or create bubbles or fissures it would create something like the figure below! The narrow black lines are a conceptual pattern of what will happen. My apologies for the poor sketching.

The necking doesn't have to be cylindrical. I tried to incorporate a bit of non-symmetry due to possible vortexes in the movement of the paste.

'

plastic movement.

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