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Impact attenuator analysis

Altair Forum User

I am doing impact attenuator analysis by mat33 material for which i have defined a sample graph (note: the coordinates of stress vs volumetric strain are same as defined in the video)

The IA is continuous compressing till the volume goes to zero and then the solver terminates the solving process. Please look over the issue soon as i have to attach this IA on full body crash model.
Also after impact it is not bouncing back
Thanks and regards,

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Altair Forum User

Hi Prasad,

can you share the engine out file instead?

Altair Forum User

Please share .0001.out (engine out) file.

Altair Forum User

This NEGATIVE VOLUME error happens when solid elements are very deformed and their characteristic length goes to 0. For large strain formulation the time step of an element goes to 0 when the element is compressed.

In RADIOSS Starter input file (Runname_0000.rad), use Ismstr =2 in the solid property and in RADIOSS Engine file (Runname_0001.rad) use the option/DT/BRICK/CST which will set the time step value tmin at which the solid elements will switch to small strain.This means that the solid elements using Ismstr =2 will use large strain formulation while their time step remains greater than tmin, and will then switch to small strain formulation.

(/DT/BRICK/CST option is used to control the time step of the analysis. The time step becomes constant after reaching Tmin specified by the user )

Please try with this option.