Choosing the right element is one of the first and most important decisions in a finite element model. This Book Byte presents the basic building blocks of the element library, the criteria for selecting an element, and a summary table of 1D, 2D and 3D elements with their degrees of freedom and typical uses.
Types of elements used in FEA: the basic building blocks
- The 1D truss element
- The 1D beam element
- The 1D spring element
- The 2D shell element
- The 3D solid elements
- Special elements
Each element is also characterized by its geometry, size and shape, and by its order: linear versus quadratic elements.
Element selection criteria
The criteria to consider when selecting an element are:
- Element type: is it a 1D, 2D or 3D problem?
- Degrees of freedom: what do you want to transfer?
- Capabilities: axial, shear, membrane, in-plane, out-of-plane behavior, and so on.
- Cost: the more degrees of freedom, the more expensive the element is in running time.
- Accuracy: for a given topology, certain elements capture a given structural behavior more accurately than others. It is therefore important to know the accuracy of each element you use.
How to choose the right element
- Predict your structure's behavior.
- Experiment with your library of elements.
- Make sure you understand the required dimensions for each type of element.
- Make sure you understand the limitations of each element.
Types of elements used in FEA: summary
- 1D elements (line): used when one dimension is very large compared to the other two.
- 2D elements (surface): used when two dimensions are very large compared to the third.
- 3D elements (volume): used when all dimensions are comparable.
| Element | Dimension | DOFs | Examples of practical usage |
|---|---|---|---|
| Truss | 1D (line) | 1 or 2: axial and/or torsion | Rods; long, slender parts connected by hinges; panel stiffeners (stringers); beam caps |
| Beam | 1D (line) | 6: 1 axial, 2 transverse shear, 2 bending, 1 torsion | Shafts; beams and columns; fasteners; pin joints; vertical posts |
| Spring | 1D (line) | 6 directions defined by the analyst | Fasteners; interfaces |
| Membrane | 2D (surface) | 2: in-plane translations | Fabric-like parts; thin metal shells |
| Plate | 2D (surface) | 3: 1 out-of-plane translation, 2 out-of-plane rotations | Pressure vessels; auto body parts; ship hulls |
| Shell | 2D (surface) | 5: 2 in-plane translations, 1 out-of-plane translation, 2 out-of-plane rotations | Panels, sheet metal, parts with a width to thickness ratio above 10 to 20 |
| Solid | 3D (volume) | 3: all translations | Bulky parts such as fittings and engine blocks |
Go further
This Book Byte is taken from Chapter 7 of Practical Finite Element Analysis for Mechanical Engineers by Dominique Madier. The topic is covered in depth, with worked examples, in the on-demand course Practical Basic FEA.
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