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Deformation of polymer-magnetic composite
Posted Jul 5, 2023, 4:28 a.m. EDT Electromagnetics, Structural Mechanics Version 6.0 2 Replies
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Greetings In my simulation I am modelling behaviour of two Iron magnets embedded in polymeric scaffold under external magnetic field. The objective is to obtain the deformation of the scaffold for various magnitude and direction of externally applied magnetic flux. The model works well for small external fields and deformations (strain of up to 3%), however in case of larger displacements the solution is not reaching convergence. From what I can see, solver calculates unreasonable solutions for deformation, resulting in large error values. I tried to restrict boundary movement in various ways to "force" convergence but to no avail.
I would greatly appreciate any advice on this issue. All the best, Piotr
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Two possible causes that immediately comes to my mind:
The material model is used outside its stable region. For example, a Linear Elastic Material is sensitive to large compressive strains, as discussed in the section Geometric Nonlinearity in https://www.comsol.com/blogs/modeling-linear-elastic-materials-how-difficult-can-it-be . You may then need to use a material model that can represent the actual physics better.
There is a 'pull-in' instability (the resisting force in the solid increases slower than the attractive force between the magnets). In that case, you would need to use an auxiliary sweep while applying some type of displacement control.
It may even be a ccombination of the two.
-------------------Henrik Sönnerlind
COMSOL
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Hello Thank you for your help. Regarding point 1, I tried to use mixed formulation but it did not improve the problem. I understand in this case, that I should try a hyperelastic model (such as Mooney-Rivlin), but I don't have this subnode available- do these models require any extra add-ons? Regarding point 2, I am not sure if I understand that. The study is time-independent so I don't know how a resisting force can increase "slower". Also, what type of displacement control should I use to ameliorate that? Should I restrict certain boundaries to move only along a defined axis? Kind Regards, Piotr