Removing an Instance in an Explicit Step

[luc46552]

Hello, I am making a simulation where I want to remove a part instance in an assembly after several steps. The first three steps are in Abaqus/Standard, and the final step imports the simulation to explicit. I now need to define a new step where one of the part instances is removed to trigger a reaction. In Abaqus/Standard, I am aware that you can use *MODEL CHANGE, REMOVE to remove an instance after the initial step, but I was wondering if there is a counterpart that exists for Abaqus/Explicit. I am also considering trying something with element deletion, but the former solution would be much simpler if at all possible.

 

[FEA way]

What is the reason for this removal ? What is it supposed to simulate ? If the part becomes destroyed in real-life then element deletion is an option. If the part is disengaged from the assembly then maybe you can just move it away using appropriate boundary conditions.

Apart from what you've mentioned (model change and element deletion) there's also so called element progressive activation (often used for additive manufacturing simulations) but it also requires Abaqus/Standard solver instead of Explicit. Maybe you could add new step in Standard, remove that instance and then import to explicit. Depends what you actually want to simulate.

 

[luc46552]

The simulation if of a so-called "stick bomb", made of popsicle sticks. When one of the end sticks is released by a user, the other sticks fly apart due to the stored energy. Videos of the "cobra weave" configuration exist on the internet if you want a physical demonstration. I am trying to remove one of the end sticks to trigger its detonation, it can be of any means as long as it disappears or no longer interacts with the other sticks.

I currently have a simulation that works entirely in Abaqus/Standard, but it is unstable and will not converge easily with a large number of sticks. It often requires significant contact stabilization due to the large displacements during detonation. Converting the final step to explicit allows the simulation to run faster and with more accuracy. The difficulty here is that, in order to prevent excessive distortion and an eventual crash, I have to use general contact instead of a series of surface contacts between the sticks. This is because general contact computes he initial displacements of the surfaces in a way that allows the sticks to reach an equilibrium when converting from standard to explicit without significant distortion. With this in mind, I cannot simply remove one of the constraints, since general contact is either on or off. I'm just very surprised that there isn't a way to remove an instance in an assembly during a simulation for explicit like in standard...

Either way, could there possibly be a way to exclude a set of surfaces from the general contact algorithm? It this were possible, I could exclude one set of surfaces and instead constrain them using surface contact. Then, I could remove the surface contact to detonate the stick bomb.

 

[FEA way]

Yes, you can use *CONTACT EXCLUSIONS to exclude surface pair from GC definition. However contact pairs are automatically excluded from GC.

I think that the only option is to use element deletion and make all elements of selected instance fail due to some small load.

 

[luc46552]

I found a solution that was simpler than that. I was able to use a displacement BC on one of the triggers to move it, as one would do in real life.