Piezoresistive Shell
The Piezoresistive Shell feature is an extension of the Conductive Shell. It offers the possibility to set up a multiphysics coupling with the corresponding structural Shell and Layered Shell physics interfaces to model piezoresistive devices, for which the electric conductivity depends on the mechanical stress or strain.
This feature requires the MEMS module. More information can be found in The Piezoresistivity, Shell Interface and The Piezoresistivity, Layered Shell Interface sections of the MEMS Module User’s Guide.
Layer Model
When the Shell Type is set to Layered shell, by default the Layer Model is set to General which considers a full equivalent 3D representation of the model. For this case, the Layer Model section provides an extra option Highly conductive layer. By selecting the Highly conductive layer, the feature enforces the potential to be constant through the thickness of the selected layers. For conducting layers where very small electric potential gradients exist in the perpendicular direction, such a setting could increase numerical stability.
When working with layered shells, you almost invariably take the material data from what has been defined using Layered Material Link, Layered Material Stack, or Single Layer Material nodes. It is however possible to override some data from a Piezoresistive Shell node too. In order to have a correct model, all layers must have been assigned material data for all boundaries selected in the settings for the interface. You can have several Piezoresistive Shell nodes with the same (or partially overlapping) geometrical selections, but with different layer selections.
out-of-plane material orientation
This section is present only when the Shell Type is set to Layered shell. For the material data inputs, you can select to Use the laminate coordinate system with the following three options:
•
No change (default)
•
Swapped normal and 1st tangential direction
•
Swapped normal and 2st tangential direction
When the Shell Type on the physics interface is set to Nonlayered shell, this section will be replaced by a standard Coordinate System Selection section.
Constitutive Relation Jc-E
Select a Constitutive model — Piezoresistance form or Elastoresistance form. For each of the following, the default uses values From material. For User defined enter other values in the matrix or field.
•
Specify an Electric conductivity, zero stress (SI unit: S/m). This typically comes from the material added under the Materials node.
•
For Piezoresistance form, select a Piezoresistance coupling matrix Πl (SI unit: Ω⋅m/Pa).
•
For a Elastoresistance form, select an Elastoresistance coupling matrix Ml (SI unit:  Ω⋅m).
When the Piezoresistive Shell node is added in the absence of an active multiphysics Piezoresistivity coupling node, the material will behave similarly to a Conductive Shell node with the electric conductivity corresponding to the entered value of electric conductivity at zero stress. The piezoresistive effect will be not included in the corresponding equation system.