Hello guys. I am currently trying to model unloading (springback) after bending. I tried making the stamp go back in the second step and modeling the change to remove the stamp, but they are not working. With the stamp going back, it calculates for one increment and then breaks. With the model change, I remove the stamp and contact pair, and then the workpiece starts moving somewhere:
Also, I don’t know why the stamp is still there.
Can somebody help with this problem?
Here is the inp file with umat:
bending - Google Drive
You don’t have to remove the stamp, just the contact pair so that the workpiece and the stamp don’t “see” each other.
You should provide some minimum constraints to the workpiece so that it doesn’t fly away. Ideally symmetry plus whatever else is needed to fix the rigid body motion (well-defined symmetric model may need fixing just one node in one direction then). The other boundary conditions can be removed with OP=NEW.
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Thank you for the reply. I added a rigid body to the stamp and matrix, and also added a constraint on the workpiece on the Y axis. It didn’t help. Can you explain more on how that’s done? Or maybe you have an example of that?
You should constrain the workpiece in all directions (to prevent all RBMs), but without overconstraining it. You could use the 3-2-1 method, but the easiest way is to utilize symmetry.
There are some examples in Abaqus documentation. They use import technique (transfer between implicit and explicit solver), but you could check how they constrain the model utilizing symmetry (their models are typically axisymmetric, though).
Thank you for the suggestions. I tried this 3-2-1 method on a simpler model in Prepomax. As I understood, I fixed 3 points on 1 plane in the X axis, 2 on the second plane in the Y axis, and 1 on the third in the Z axis. On the second step, the workpiece just explodes. With symmetry, the same thing happens. I fixed one surface on the X axis, the second on the Y, and one point on the Z. Same thing, the workpiece explodes.
You could also use soft springs. But did you try without UMAT (just a homogeneous steel workpiece) ? Can you share the geometry in the STEP format ?
