Basic Understanding of Finite Element Analysis: Element Types and Orders

N here denotes node and E denotes as element.

As can be seen on the above picture, there are 4 nodes and elements on the left and 3 nodes and elements on the right side.

For 2nd order elements, 2nd order elements consist one additional mid nodes between corner nodes. On the left side, there are 8 nodes and 4 elements. And there are 6 nodes and 3 elements on the right picture. The order difference between would result in the deformation can be capture more accurately, at the same time more computational costly.

2. Element types

What is element types? First, let’s look the definition “Element types are defined in the input file with ANSYS ‘ET’ commands. The element type number is assigned by the interface program. The same element type can be defined twice with two different numbers if its material or/and physical properties are different from one to the other.” If this explanation is too rocket science, let’s break it down to a more easy way!

There are 2 Main Elements: Tetrahedral (left) and Hexahedral (right)

And 2 Transition Elements: Prismatic wedge (left) and Pyramid (right)

Let’s continue and start the 2D element introduction. There are two basic 2D element: Tri and Quad

This element type behaves rigidly and should always avoid using.

2. TRI 6 (2nd order)

This element type uses Quad mesh and would result better mesh quality.

3. Quad 4 (1st order)

This element type decreases the number of elements and also reduce rigidity.

4. Quad 8(2nd order)

This element type would deform better and result in better mesh quality, still at the same time increase computing time.

For 3D elements, it is probably the most general solid finite elements since the field variables are dependent of x, y and z. For 2D elements, there is less Degrees of Freedom to be considered. That means less accurate but compute more fast. In the application, if the model is somehow “flat”, it can be used as Shell model to reduce the dimension.

This is probably the most disputed element type in FEA, this is easily created but performed badly.

2. TET 10 (2nd order)

This element type behaves like TRI6.

3. HEX 8 (1st order)

This behaves like Quad4, but imagine when there is a beam and the only layer (thickness) is HEX8, this would perform badly.

4. HEX 20 (2nd order)

Best element type, we should always use this element type in theory. But in reality, it is hard to mesh a model with all HEX 20.

And the last question would be: how to get best mesh (optimize mesh)? Let’s find out next time!

Reference

What are the Types of Elements Used in FEA (https://enterfea.com/what-are-the-types-of-elements-used-in-fea/)

2D vs 3D Finite Element Analysis (with examples) (https://enterfea.com/2d-vs-3d-finite-element-analysis/)

Ansys Finite Element Analysis (https://www.udemy.com/course/ansys-finite-element-analysis-and-industrial-applications/)

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