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Material Behavior after stress exceeds ultimate tensile strength limit

I ran a simulation with a non linear material ( Having a stress strain curve data upto its ultimate tensile stress). In the simulation results, the von mises stress exceeds the limit of stress I have entered in the curve data.

What is happening here? Is the software extrapolating from the data OR assuming zero resistance from the regions where the von mises stress has exceeded the ultimate limit.

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Radioss

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Altair Forum User

It seems that in case of blank parameters left in the em category of MAT/LAW36, the software extrapolates the stress strain curve ( a conservative assumption). However if you want the material to stop effecting the system as soon as the limit is reached, don't forget to put the respective em value in the card.

Another workaround is to provide a complete stress strain curve where the stress goes from zero to zero. I personally prefer the later method as it leaves no scope for any more confusion.

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Altair Forum User

The data you provide refer to the behaviour of the material under tension in each direction. The von Mises criterion contains multiple stress components and therefore what you describe in the first post is reasonable. What you should check is whether the individual normal stress components (sigma_xx, sigma_yy) exceed the values prescribed. My guess is that they don't. At least not much.