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# Simulate anisotropic thermal behavior with a structurally isotropic hyperelastic material?

## Simulate anisotropic thermal behavior with a structurally isotropic hyperelastic material?

(OP)
Hello,
My project is the FEA of a photoresponsive cantilever, it bends when it is irradiated with light and the bending direction depends on the light wavelength. To do so I'm using the software Marc Mentat 2015 and using the subroutines UELASTOMER and ANEXP to program the hyperelastic behavior and the cantilever bending due to irradiation (I'm considering the photo bending is analogous to the thermal bending). The issue I'm having is that the software assumes isotropic thermal expansion when it is hyperelastic isotropic, so the same expansion is considered in X, Y, and Z directions, which leads to inaccurate analysis. I'm not so sure if modeling the material as structurally orthotropic or anisotropic would be convenient because, in reality, the material does not have any preferred orientation whatsoever. Is there a way to simulate the thermal anisotropic behavior with the isotropic hyperelastic material model?

### RE: Simulate anisotropic thermal behavior with a structurally isotropic hyperelastic material?

Maybe you could use aniso-/orthotropic hyperelastic material model but set it in such way that the mechanical behavior is the same in all directions (so it’s actually isotropic). This way you would be able to include anisotropic thermal expansion.

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