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What is Finite Element Analysis (FEA)?

Finite element analysis is a mathematical process that can simulate physical, real-world conditions inside of a digital environment. FEA is a very useful tool in design, as it allows engineers to asses the validity of their model without having to conduct a large number of real-world tests or experiments. Take the design of an armchair for example. If an engineer would like to know the feasibility of their current design, without using any digital simulations, they would have to conduct lengthy physical testing of the chair to determine the eventual modes of failure. This information would be used to improve the design, and the lengthy testing process would begin again. This would continue until the engineer was satisfied with the testing results of their model. However when using FEA, the physical testing conditions can be defined in the software, and the program will simulate 1,000,000 cycles of loading. The results of this time-efficient simulation (modes of failure, cycles before failure, etc.) can then be used to improve the design. Once the design has been changed, the updated parameters can simply be input into the software, and the simulation can be run again. This results in a significantly accelerated design cycle.

FEA Workflow

For this project, FEA simulations were carried out using the ANSYS Discovery AIM 2020 R2 software. This software can be used to run many different types of simulations, such as: structural, fluid flow, thermal, and electromagnetic. The necessary steps that must be completed in order to set up and run a structural simulation, as well as properly interpret the simulation results, are described in detail below. The pictures shown throughout correspond to an example structural simulation run on an armchair geometry. There are three main sections to the simulation workflow: "Geometry", "Physics", and "Results".

Geometry

The first step in creating a simulation in Discovery Aim is to import the geometry of the part or assembly that is being studied. This can be done using the following steps:

1. Launch the Discovery Aim 2020 software
2. Hover over the "Structural" simulation block and press "Start"
3. Select the "Import New Geometry" option and press "Next"
4. From the pop-up file window, select the desired geometry file (Important: SolidWorks files must be imported as STEP files in order to be compatible with the software)
5. Once the geometry is visible in the workspace, press "Finish"

Once properly imported, the geometry task will display a green "Up-to-date" notification. This signals to the user that no more changes need to be made to this section before the simulation can be run. If needed, there are options under this tab to edit or replace the geometry.

Note: Under the current student version of the software, any geometry imported is subject to a limit of 50 bodies and 300 faces.

Physics

Material Assignments

In order to run a simulation, every single body in the imported geometry must be given a material assignment. This means that during the simulation calculations, each body will be treated as its designated material with its specific corresponding properties (density, Young's modulus, yield strength, etc.). Material assignments can be set using the following steps:

1. Under the "Physics" tab, select the "Material Assignments" option
2. Click the "Body selection" tool on the top right side of the workspace
3. Select a body and press the "Replace with selected entities" button that will have become blue
4. If any other bodies in the geometry are the same material as the previously selected body, select those bodies and press the "Add selected entities" button
5. Once all bodies of a common material have been added, click the "Material" drop-down menu and select the desired material (if the desired material is not a pre-defined material, select the "Create New" option and specify known properties)
6. Return to the "Physics" tab. For any other sets of bodies that share a common material, select the "Add" option besides "Material Assignments" and repeat the above steps

Structural Conditions

The next step in setting up the simulation is the most important. The structural conditions section is where you will define all of the conditions that the geometry will face during the simulations. This tool can be used to define structural conditions such as forces, supports, temperatures, pressures, and many more. Structural conditions can be defined using the following steps:

1. Select the "Add" dropdown menu beside the "Structural Conditions" option and select the desired condition 
2. Fully define the parameters of the condition based on the goal of the simulation. For example, when defining a force, the faces to which the force will be applied, the magnitude of the force, and the direction of the force must all be specified
3. Repeat the above steps until all conditions desired to be in the simulation have been added

Note: A support can either be defined as the faces of the geometry that would be resting on the "ground" in reality, or by adding a body to the geometry that serves as the ground (flat slab of concrete for example), and defining that body as a support.

Advanced Setting: Interface Conditions

Interface conditions present in the simulation define how different bodies/faces that are in contact interact. For simpler geometries, this step is often not needed in order to obtain realistic simulation results, as the pre-defined conditions generated by the software are typically adequate. However for more complicated geometries, defining proper interface conditions important. There are five different types of interface conditions in Discovery Aim 2020:

• Bonded: By default, all contacts in the geometry are modelled as bonded. This means that the bodies in contact are treated as a single body and not allowed to slide, rotate, or separate from one another
• Frictional: This behavior treats bodies in contact as distinct bodies, allowing them to slide and rotate against one another with a user-specified coefficient of friction
• Frictionless: This behavior treats bodies in contact as distinct bodies, allowing them to slide and rotate against one another without the presence of friction
• No Separation: This behavior treats bodies in contact as distinct bodies, allowing them to slide against one another, but does not allow for separation
• Rough: This behavior is best used when one or both of the bodies in contact are significantly rough (ex. rough concrete surface)

Actually defining the interface conditions in the simulation can be done using the following steps:

1. In the "Physics" tab, select the "Interface Conditions" option
2. A list of automatically detected bodies in contact will be displayed, ensure that the software did not miss any contacts
3. For any contact for which bonded behavior is not suitable, click on the contact title
4. In the "Contact behavior" dropdown menu, select "Create New"
5. Select the behavior from the displayed list that is most suitable for the given contact
6. Repeat the above steps for all necessary contacts

Solving Physics

Once all of the necessary simulation parameters have been defined, the physics task will display a yellow "Out-of-date" notification. This signals to the user that no more changes need to be made to this section before the simulation can be run. At this point, the user may click the "Solve Physics" button to begin running the simulation calculations. Depending on the complexity of the model, the solution process can take anywhere between a couple of minutes to a couple of hours to complete. Once the solution is complete, the physics task will display a green "Up-to-date" notification.

Results

Once the simulation physics have been updated, the results will become available. Contour plots of equivalent stress and displacement magnitude are the two results that are generated by default. However, the user can also add their own custom results such as fatigue life, strain, force reaction, and much more. In order to add a specific result, simply navigate to the "Results" tab, click the dropdown menu beside the "Results" option, and choose the desired result type from the display. Once all desired result types have been added, the user will need to press "Evaluate Results", after which, all off the added results can be viewed individually.

When viewing a result, the value and location of the maximum and minimum calculated values are automatically displayed. Appearance settings such as "variable range", "coloring", and "color distribution" can be varied under the "Appearance" tab to fit the needs of the user. Changing these settings can make it easier to view and understand the results for specific areas of the geometry.

For geometries with more than one body, the "Location" option under the "Definition" tab can be used to specify which bodies the results are evaluated for. By default, results are generated for all bodies in the assembly. However, choosing only specific bodies can make it easier to determine the maximum and minimum result values in these bodies (especially when those values are not the maximum and minimum values of the overall geometry).