Developed By: Kevin Giordano and Abby Speckhals

FEA walkthrough from powertrain meeting but the video conveniently cuts out bc I don't know how to screen share in zoom

Intro to FEA PowerPoint

What is FEA?

FEA is used for many areas of simulation, but in NER (and therefore in this lesson) will cover static simulations of 3D solids using SOLIDWORKS Simulation.

The model is broken down into a mesh, a series of triangles, that approximate the geometry of the part in question. From there, linear algebra is used to solve a large system of equations to determine the stress on each cell. This allows more complicated geometries to be solved than by hand.

Boundary conditions must be set to run the study. These are: loads and fixtures. Loads are the forces, moments and so on that act upon the part. These are what the part must be able to withstand. Fixtures are what hold the part in place. There are several types of fixtures, that restrain the part in different ways.

These questions are all answered by running FEA!

1. Setup

To set up a study, navigate to the Simulation tab in the menu, and select New study. From there, select a static study.

4. Mesh

The first step in FEA is to create a mesh in solidworks. When considering a mesh, the size of the mesh is critical. A finer mesh will have more cells, which can be more accurate, but will take longer to run. A fine mesh can also have singularities that introduce error in the study. These can exaggerate the stress at a certain area. They can happen at split lines and corners.

To create a mesh, select the arrow under run this study, and select create mesh.

Open

The easiest way to change the mesh size in solidworks is to change the mesh density. Usually I set the mesh to its finest as a default. The image below shows this slider. The mesh quality tab can be used to set more fine meshes. We will revisit the mesh quality later.

Open

Mesh Density Slider

To run a FEA study, the boundary conditions must be determined, and the part must have a material assigned with properties in solidworks.

Boundary conditions are made up of two sub categories: loads and fixtures. The table below lists some of the boundary conditions that solidworks has, and a little about them. These are very similar to the fixtures that are used in Statics and Mechanics of Mateirals

2. Fixtures

3. Loads

A part must have at least one load, and a combination of fixtures that fully constrain it. For example, a single roller slider joint is not enough to fix a part.

To apply a fixture, select the arrow under the fixtures advisor, then click on the fixture type desired. For this tutorial, select fixed joint.

From there, you must select the faces, edges or points that you want to fix. Select the top face of the part as shown, then press the check mark to confirm.

To apply a force, press on the arrow under the external loads advisor.

From there, select force, and click the right face of the part, as shown below to apply the force to there, just as with the fixed geometry.

By default, the force is set as normal to the plane, and to 1N. For this, we will eave the force as normal to the face. Now, set the force to be a value of 400N, and confirm with the green check.

At this point, the simulation is ready to run! When you click run this study, the computer will first mesh the part, according to the mesh setting set earlier (if there is no mesh already), then the computer will run the simulation.

5. Results and Validation

Next the results of the study must be visualized.

By default, solid works gives a plot of the stress, strain and displacement. On the stress, plot, you can see the stress on each point in the mesh. The bar chart on the right shows the numerical value of the stress. The red arrow shows the yield strength of the part. If it is below the bar chart, the entire part has less stress than the yield strength. If it is on the chart, some of the part has more stress than its yield strength. If the above procedure is followed, the stress should look like this:

As you can see, the stress is highest at the sharp corner, which creates a stress concentration. Try placing a fillet here, and see how this affects the stress in the part.

One useful plot that solidowks does not create automatically is the factor of saftey plot. to create this, right click on results, and select factor of safety distribution.

Next, select the checkbox that limits the maximum FOS to 3.0. This is important to allow the areas with lowest FOS to be highlighted. If this is not selected, it will be hard to discern which areas of you part have a FOS of 1.0 from 2.0, because the gradient of colors must stretch over a long range, as many areas of the part will have low stress, and therefore a high factor of safety.

Once you have run the study, there are many ways to validate the results. Here, we will cover the effect of mesh size. Ideally, if the mesh is changed, the results of the study should not change. Therefore, it is good practice to run the study with several different meshes and determine the change. Below is the same study, run with a less fine mesh.

With all else being equal, reducing the mesh size for this part increases the factor of safety in the area of the corner. Since the study was originally run on the most fine default mesh size, to make the mesh more fine, the advanced settings must be used. One way that this can be done is reducing the maximum and minimum element size. I changed the maximum to be 0.04 in and the minimum to 0.03 in, as shown below.

The mesh will then look like this:

These settings will result in the following FOS plot, showing that the factor of safety decreases further with the finer mesh. This shows the issues with sharp edges in FEA. Additional to sharp edges causing actual stress concentrations, FEA can have issues with sharp corners.

Once the corner is filleted,

Here, as the mesh was varied, the results did not significantly change. this give confidence that the results are accurate, and are not caused by inaccuracies with FEA.

Best Practices in Fixtures and Loading

Before running FEA on a part, the first step should be to draw a proper free body diagram for the part. From there, the type of each reaction and force should be determined. For example, it should be determined what directions that reactions and forces should be applied in.

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