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The CST element

The simplest two-dimensional element is the linear triangle, often called CST (constant strain triangle). The displacement field inside the element is linear, which makes the strain – and hence the stress – constant throughout the element.

ε=constant in the element\varepsilon = \text{constant in the element}CST: linear displacement gives constant strain

Symbols

ε\varepsilonstrain

Example

In a region with a steep stress gradient (e.g. near a hole),

CST elements must be very small to capture the variation well.

Use a fine mesh or higher-order elements where the stress varies a lot – not CST alone.
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Part of Finite Element Method: Element types, meshing and error.