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For the occupant cell load cases (front, side, and rear), solid element analysis for the entire frame is utilized as final verification to ensure our frame design meets regulations for the occupant cell (max and min principle stress, Von-Mises/equivalent stress, total deformation, and factor of safety).
This setup follows the exact same as the beam element analysis, in terms of force and support setup, it just utilizes solid elements to achieve more accurate values. This will greatly increase runtime but because this is used only for final results, it is used mearly to validate the results of the beam element simulation.
Roll Cage Solid Element Analysis (for iteration and final results)
For the roll cage load cases (all 10), solid element analysis for the roll cage is utilized to iterate and use as final verification to create and ensure our roll cage design meets regulations (max and min principle stress, Von-Mises/equivalent stress, total deformation, and factor of safety).
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To start, because only the roll cage will be utilized for solid element analysis (due to the runtime concerns of a full chassis as solid elements), we need a way to accurately model stress propagation from the roll cage to the rest of the chassis, without actually having the chassis modeled. We will do this by creating deformable joints at each tube coming from the roll cage while utilizing a specifically calculated stiffness matrix for each joint. Additionally, weak springs are turned on, to ensure the model will be constrained just enough to not have rigid body motion occur. This allows each joint to accurately deform itself, while acting as if stress is propagated to the rest of the chassis, which is more accurate than utilizing fixed supports, that would act with infinite stiffness and create a more conservative simulation process (which means we would end up overbuilding our frame).
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Next, utilize this MATLAB file, in order to calculate the respective stiffness matrix to be imported into Ansys for each joint. You will need material properties (that can be found from ANSYSon sharepoint), as well as properties of each tube. This includes, elastic modulus (E), shear modulus (G), tube outer diameter (OD), tube wall thickness (WT), as well as the length of each tube not modeled (meaning the length of the tube that was cut off the design, as each joint represents a point on that tube acting as a cantilever beam). All of these inputs need to be made in imperial units (this follows the unit convention from our tube sizes).
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The output will mimic that of the stiffness coefficient matrix shown in Ansys Workbench on the individual general joints. This stiffness matrix essentially gives the joints of the tube a set stiffness instead of an infinite one, to allow for more accurate stress propagation. I chose to have the MATLAB code directly output the same matrix, so that the only work for you to do is directly transfer the values from MATLAB into the matrix on Ansys.
How the MATLAB code for the RC sims works read this
After inputting the values, you then must ensure that each joint has a proper reference axis and face selected, to ensure that the stiffness values are then utilized in the proper orientation and situation.
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Do this for every joint, ensure that weak springs is on, and the support settings for the simulation is finished.
In terms of force placement and calculation, the load cases vary from 5g, 4g, and 1.5g. These are all reliant on the force of gravity affecting the entire weight of the car, which is associated with the total mass of the car. Additionally, these are placed at the top of the roll hoop, for the front and the back, depending on the desired sim. Additionally, you may need to take the cos/sin value of a force value depending on specific load cases that ask for a force at a vectored angle.
Finally, you should now be able to run the sim and get accurate results with in minutes, due to the reduced size of the model while also still utilizing solid elements.