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Inverted mesh elements during snap-back of a snap-through structure with stiff shutters

Posted Oct 3, 2026, 1:23 p.m. EDT Mesh, Studies & Solvers, Structural Mechanics Version 6.3 0 Replies

Zeyin BIe

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Hello, I am modeling a 2D plane-strain transient thermo-mechanical snap-through structure in COMSOL Multiphysics 6.3. The structure consists of a curved soft beam with a thermally contracting active layer. Heating causes the beam to snap through. Two long and relatively stiff shutters are attached to small soft silicone pads/protrusions on the beam. After snap-through, the shutters block the incident light, the structure cools, and eventually snaps back. The main problem occurs during snap-back. The computation becomes extremely slow, the time step decreases dramatically, and COMSOL reports inverted mesh elements. The inverted elements are consistently located near the connection between the stiff shutter base and the soft pad underneath it. The soft beam and pads are modeled as silicone with a Young's modulus of approximately 2 MPa. The shutter is much stiffer and relatively thin. Geometric nonlinearity is enabled and a time-dependent solver with Generalized-alpha time stepping is used. I have tried several approaches: 1. Assembly + identity pair + compliant thin layer between the pad and shutter. I also reduced the shutter Young's modulus to approximately 0.5 GPa. This improved convergence and prevented immediate mesh inversion, but the computation became extremely slow. About two snap-through/snap-back cycles required approximately 21 hours. 2. Different geometries, including attaching the shutter directly to the beam and attaching it through a small protrusion/pad. The problem still occurs near the shutter root. 3. Local mesh refinement and different mesh configurations near the shutter/pad interface. 4. Reducing the maximum time step around the snap-through and snap-back events. 5. Rigid/stiff shutter modeling and rigid-flexible connections. Large local deformation still develops in the soft material near the shutter root during snap-back. My main questions are: - Is this inverted-element problem more likely caused by the geometry/interface design, the mesh, or the nonlinear solver/time stepping? - What is the recommended way in COMSOL to connect a very stiff and thin shutter to a very soft silicone substrate undergoing large deformation? - Would a rigid domain with a compliant connection/thin elastic layer be more appropriate? - Would automatic remeshing or an ALE approach be suitable for this type of snap-through/snap-back problem? - Are quadrilateral elements or another local meshing strategy preferable to triangular elements in the highly deformed shutter-root region? - Are there solver settings that can handle this instability more efficiently without forcing the time step to become extremely small? I have attached figures showing the overall structure and the location of the inverted elements during snap-back. Any suggestions on the geometry, interface modeling, mesh, or nonlinear solver settings would be greatly appreciated. Thank you.

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