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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. The purpose of FEA is to solve structural, vibrational, and thermal problems in a virtual environment before they become problems in the real world [1]. 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 in Ansys

For the Armchair Life Cycle Testing 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".

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. 1. 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. 1. 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 is 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. 1. 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.

FEA Simulations in Solidworks

In Solidworks you can perform simulations on parts and assemblies. There are 3 simulation packages that control the number of simulations you can use [1]. Simulation Standard offers structural, motion, and fatigue analysis [1]. In addition to Simulation Standard, Simulation Professional offers frequency, thermal, buckling, drop test, and optimization studies [1]. In addition to Simulation Professional, Simulation Premium offers the ability to analysis analyze plastic and rubber components, metal forming operations, composite materials, and dynamics loads such as oscillating or vibrating structures [1]. The Student Edition of Solidworks comes with Simulation Professional. 

Starting a Simulation in Solidworks

Navigate to the Solidworks Add-Ins tab and click Solidworks Simulation. Once it appears, select the Simulation tab. Select the type of study you want to perform, name it, and then click the checkmark to enter the study.

Apply Material

The Apply Material command changes the material and thus the object's properties in the simulation.

Fixtures

Fixtures are constraints applied to faces of a model that support the model. Fixtures can be fixed geometry, roller/slider, fixed hinge, elastic support, or advanced fixtures involving reference geometry. If you only want to apply the fixture to part of a face use Split next to Type at the top of the fixture sidebar to create a sketch that splits the face. If you are unsure of how to use fixtures use the fixture advisor.

Loads

Loads are the condition you are simulating on the model. Loads can be force, torque, pressure, gravity, centrifugal force, bearing load, distributed mass, temperature, flow effects, thermal effects, and prescribed displacement. If you only want to apply the load to part of a face use Split next to Type at the top of the load sidebar to create a sketch that splits the face. If you are unsure of how to use fixtures use the loads advisor.

Connections

Connections are used in an assembly to connect parts of an assembly. Connections can be springs, pins, bolts, and bearings. You can also use contact set and component contact to connect parts. Using connections for springs, pins, bolts, and bearings is important because in the simulation, connections act like they would in the real world and do not require simulating a complex model of the part. Using connections instead of modelled parts saves a significant amount of time because you do not need to model that part and the simulation calculates faster. If you are unsure of how to use fixtures use the connections advisor. Most connections cannot be simulated in large displacement mode, so if you are asked use small displacement mode and do not show the deformed result like in the simulation of a shaft, bearing block, and plate shown below.

Results

After you have defined the study with fixtures, loads, and/or connections, run the study. Once the simulation has been calculated, the results will appear in the side bar. After running the study, stress, displacement, and strain plots will appear in the sidebar, to view additional results such as result force and pin force add them to the results under the results advisor. The results can be hidden and shown like a sketch and you can plot additional plots with the new plot command under the results advisor. If you are unsure of how to use results use the results advisor.

References