What would happen if we applied a stress greater than the yield stress to a rigid-perfectly plastic material?

Question

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

Say that we are drawing this material through two dies, something like this:

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?

Does a perfectly plastic material have a yield stress? Wouldn't that be contradictory? — fred_dot_u, Apr 11 '22 at 14:24
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? — VJ123, Apr 11 '22 at 14:28
F=ma. If the applied force exceeds the resisting forces, the piece accelerates. — JohnHoltz, Apr 11 '22 at 16:44

score 0 · Accepted Answer · answered Apr 11 '22 at 21:33

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.

'

What would happen if we applied a stress greater than the yield stress to a rigid-perfectly plastic material?

1 Answers1