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I would actually model the parts doing the crushing and use contact.
Also, the material is non-linear (plastic deformation), so you should double-check that your material properties to be sure to account for this.
Not too sure I have your situation properly understood. However, if you want to take say circular or rectagular tube and flattend some section of it - like say the end of a tubular strut on a piece of scaffolding so that a pin connection can be drilled through the flattened area at the end. If this is the case you have a couple of complications that can arise.
Firstly you need to do a large displacement non-linear analysis with large strain, plasticity, update load direction and contact enabled. Secondly, since cosmos does not support self contact the tube has to be made of two separate bodies so that when the tube halfs come in contact when crushed together self contact is avoided (to the extent that can be achieved). Thirdly, cosmos non linear contact can be a bit tricky on the convergence side and it usually takes some mucking about to get a solution to progress past the onset of contact. Fourthly, element distortions typically limit how far you get to do large incremental strains. The acr length control method does not support contact so you may have to do a dynamic analysis to progress past the point of low stiffness as the tube x section buckles. but I would try a force controlled static solution first and see how far it gets. It might go far enough as the drop in stiffness would probably not be that sudden in this particular case.