What are the options for simulating lattices?
There are three main methods for simulating lattices in nTop. They are using Solid Elements, Beam Elements, or Homogenization. The pros and cons of each method are listed in the table with an example workflow below.
Solid elements are volumetric finite element mesh of the entire lattice structure.
- A finer mesh is required to capture the detail of the lattice
Set up an FE Solid Component block in the FE Model. Depending on the model, some mesh errors may occur. Follow these steps if so:
- Use Remesh Surface block after Mesh from Implicit Body
- Volume Mesh block may fail; if so, you can repair the mesh through Mesh from Implicit Body and Remesh Surface or use the slower, more robust, Robust Tetrahedral Mesh.
Beam elements are finite element nodes along lattice vertices connected by lattice beams. This method greatly reduces the number of elements from a typical volume mesh but ignores certain mechanical behavior like edge effects and stress concentrations in the lattice. FE nodes will be placed at the endpoints of each beam, along with node(s) and the subdivisions of the beam. You can choose the number of subdivisions as input to the FE Lattice Mesh block, which will be arrayed as demonstrated in the image below.
Set up an FE Lattice Component in FE Model. Remember that the lattice beam thickness is a field input in the FE Lattice Component block. You will need to isolate and trim the lattice elements correctly.
- Use Trim Lattice to ensure the lattice elements lie within the volume of the Lattice Structure.
- If you get a warning about short lattice beams, use Collapse Lattice Vertices with a threshold much lower than the unit cell size.
To create a homogenized simulation, run a Solid FEA simulation on a single unit cell of the lattice, and generate effective material properties of the unit cell. Next, run a second Solid FEA simulation on the bulk lattice structure volume using the effective material properties (from the first simulation).
Use FE Solid Component with the Material chip from the Homogenization block.
- Works best with many unit cells
- Good for comparing different lattice types
To compare these methods, we've created a BCC Lattice between two panels. Look for the download of this Case Study at the bottom of this article.
The images below represent a direct comparison in Displacement values and Von Mises Stress values. The images are in the same order as above (Solid Elements, Beam Elements, and Homogenization). Scroll below to see the range of values.
Below is a direct comparison of the three methods: computational time, stresses, and displacement.