What is the Ecoillini Supermileage team?
The Ecoillini Supermileage team is a student organization at the University of Illinois that is dedicated to the creation of fuel efficient prototype vehicles. These vehicles are made to compete in the Shell Eco-Marathon competition. More information can be found on the team’s official website here.
What is the breaking truss?
In our generation 5 gasoline powered car the Breaking truss supports the front breaks of the car. In the figure below it can be seen at the front of the car. They are constructed using carbon fiber tubing and connectors 3D printed using PA 2200 nylon. The part must be robust and strong enough to withstand the force of the driver slamming their foot onto the breaks.
New Design
I was able to lower of the weight of the truss by removing one of the support structures on both the left and right sides.
Finite Element Analysis
To ensure that the changes made to the design did not impact it’s structural integrity I used Solidwork’s FEA simulation add-in. I began my analysis by first looking at the 3 components that were designed to be printed as they were the ones most likely to fail. I assumed that the rider would weigh about 150 pounds and that in the most extreme scenario they would use their entire weight to hit the breaks.
When performing this analysis I assumed that the 3D printed components were both linear and isotropic when in reality it is both nonlinear and orthotropic. I simulated it as a linear material as the differences between linear and non linear materials only become pronounced after the yield stress is exceeded. I assumed it was orthotropic as I did not have reliable data concerning the orthotropic nature of the 3D printed material. I also assumed that the material had a yield strength of 50 MPa based off a datasheet I found here.
I applied the 150 pound load to the point where the breaks are attached, the setup of the simulation can be seen in the figure below.
The figures below show the resulting von Mises stresses in the model after the simulation, the scale on the right shows the colors which correspond to the stress level in Pascals. The lower figure shows these stresses only in the 3D printed components.
I assumed that the driver hitting the break pedal should be modeled as an impact load, As such the analysis of the results should take into account the impact correction factor, the formula for this factor can be seen in the equation shown below. As the initial velocity value is assumed to be zero the factor comes out to be 2.
Taking the impact correction factor of 2 into account I used the iso clipping tool to find all the areas where the von Mises stress exceeded 25 MPa, 50% of the assumed yield strength. This can be seen in the figure below.
As can be seen in the figure only a negligible region exceeds this yield strength. This region is also going to be supported by the stronger carbon fiber tubing so it can be disregarded.