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Boundary Conditions Solid Mechanics
Posted Sep 4, 2017, 10:04 p.m. EDT Heat Transfer & Phase Change, Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions, Results & Visualization, Structural Mechanics Version 4.3b, Version 4.4 3 Replies
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I'm trying to simulate a multilayered assembly of 4 different materials subjected to a temperature gradient. I want to use Comsol to validate a numerical method that I've been developing. When the interface between two adjacent layers is flat, the simulation reproduces the behavior of my code. Nevertheless, when I put boundaries that are not flat, there're differences between my code and the simulation that COMSOL provides. I want to know if it is possible to know the exact boundary condition that COMSOL is setting at the solid-solid interface (the balance equation), in order to see if I am doing something wrong or if there's an additional term that COMSOL is considering that I am not.
Thanks in advance.
Daniel A.
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The only condition at the interface is continuity in displacements (assuming nodes are shared).
Then there may be postprocessing artifacts, depending on your choice of averaging etc. in the Quality section of plots.
Regards,
Henrik
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Thank you for your quick answer. So, in addition to the displacement condition at the interface, there's no stress balance condition at the interface? Because I've been reading that this condition is necessary at the interface between two adjacent materials. How does Comsol can solve the system without both displacement and stress conditions? Or am I misunderstanding the concept? My apologies in advance if I am considering something wrong in my calculations.
Best regards,
Daniel A.
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Your questions are interesting.
In the finite element method, there is (implicitly) a force balance in each node, since that is actually what we are solving for in the final matrix equation K*u = f. But there is no explicit balance equation formed at an interface. The balance between neighboring elements work the same way everywhere.
With a standard displacement based finite element formulation, the stresses are actually discontinuous over each element boundary, even within a homogeneous material. More mathematically, we have left the exact (strong) form of the governing PDEs in favor of a weak formulation.
Regards,
Henrik