Example: Microrobot leg 3D

Introduction This model shows the movement of a silicon micro-robot leg due to thermal expansion as a function of time. The heat transfer and structural mechanics equations are solved sequentially in a time-dependent analysis. –The heat transfer problem is a transient analysis while the structural problem is modeled in a quasi-static analysis. In order to reduce the degrees of freedom a geometry simplification was required for the 3D model removing two layers: –The thin highly-conductive layer and poorly conductive layer are modeled with the thin conductive shell application mode from the heat transfer module and stiff spring temperature boundary conditions respectively. –The shell element application from the structural mechanical module is used for modeling the mechanical part.

Geometry Heating resistors Cured polyamide (high thermal expansion coefficient) Silicon leg

The general heat transfer equation: The principle of virtual work for the structural mechanics Domain Equations

Boundary Conditions - heat Highly conductive layer & stiff spring condition Highly conductive layer only Convective flux All other boundaries have thermal insulation conditions

Boundary Conditions – structural mechanics No displacement Structural shell element including thermal expansion All other boundaries are free to move

Results The microrobot leg bends due to the heating of the leg

Results The maximum displacement at the tip of the leg is 0.6 mm for a heat source of 2e 13 W/m 3 during 9 ms.

Results The highly conductive layer and the stiff spring condition accurately model the thin layers.

Results - Animation

Conclusion A thermal stress analysis is straight forward to perform in the Structural Mechanics module Model shows the possibility to replace thin layers by a specific boundary condition, and save memory: –Highly conductive layer boundary condition (already implemented) –Stiff spring condition to model a poorly conductive layer –Direct coupling of shell and solid element in structural mechanics Large transient multiphysics problem solve sequentially using quasi-static analysis and the manual definition of the linearization point.