# Couple Stress

Couple Stress Mixed Triangle/Quadrilateral

* Number of Nodes: 3, 4, 5, 6, 7, 8
* Number of DoFs: 3 (Translation, Translation, Rotation)
* DoF Label: U1, U2, UR3

## References

1. [arXiv:2207.02544](https://arxiv.org/abs/2207.02544)

## Syntax

```
element CSMT3 (1) (2...*) (3) [4] [5]
element CSMT6 (1) (2...*) (3) [4] [5]
element CSMQ4 (1) (2...*) (3) [4] [5]
element CSMQ5 (1) (2...*) (3) [4] [5]
element CSMQ6 (1) (2...*) (3) [4] [5]
element CSMQ7 (1) (2...*) (3) [4] [5]
element CSMQ8 (1) (2...*) (3) [4] [5]
# (1) int, unique element tag
# (2...*) int, corresponding number of node tags
# (3) int, material tag
# [4] double, thickness, default: 1.0
# [5] double, characteristic length, default: -1.0
```

## Remarks

1. The geometry definitions of CS elements resemble those of CP elements (e.g., CP3, CP4, CP5, CP6, CP7, CP8).
2. The characteristic length `[5]` can be left as default value (negative) to automatically determine the value based on geometry (square root of area), or set to a positive value to manually specify the fixed length.
3. Currently, only supports [`Elastic2D`](https://tlcfem.gitbook.io/suanpan-manual/material/material2d/elastic2d).


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