Goal: MSXIV requires a detailed overview of the different possibilities for incorporating composites as structural components into the chassis.
Context: In MSXII, the majority of the composite use was for the aerobody. The aerobody was mounted to the chassis and was not designed to be a structurally component of the car. In essence, the aerobody and chassis systems were isolated from each other. The main advantage of this was to avoid the mistakes made with the monocoque design used in MSXI, which are detailed in other confluence pages. By having a strong, overbuilt chassis, the car had a reliable structure which is something that MSXII did very well.
The push for using composites as structural members was inspired by a few factors. At ASC 2018, the team had the opportunity to see the use of composites in other cars. There are many advantages to using composites including weight reduction, better use of space and higher strength. However, the use of these composites requires lots of knowledge and experience and a well defined schedule. In order for this to be successful, the team needs to research the various possibilities and perform materials tests to validate the reliability of the material.
| Material/Material combination | Properties | Manufacturing and forming process | Cost |
|---|---|---|---|
| Carbon fiber Aluminum honeycomb sandwich panels | |||
| Carbon fiber and nomex sandwich panels | |||
| Balsa core |
University of Toronto Composite Sandwich Panel Forming:
Goal: Determine a method for manufacturing composite sandwich panels.
Background: The bottom section of the chassis will use carbon fiber sandwich panels due to their high torsional stiffness. There is a broad base of knowledge from various student design teams that can be utilized to help us determine the best solution that optimizes the key criteria:
- High torsional stiffness
- Reliable, will not fail catastrophically
- Manufacturable with the team’s resources
- Cost effective
- A large safety factor to account for manufacturing defects
https://www.mie.utoronto.ca/mie/undergrad/thesis-catalog/319.pdf
According to this thesis, the UofT FSAE team optimized the design of their sandwich panels by using a software called Altair OptiStruct. They also used Pro/Engineer and Pro/Mechanical. Their layering consisted of carbon laminate plies, a thin layer of fiberglass cloth to ensure an adequate bond to the core material, then the nomex core material. To ensure a firm bond of the carbon laminate to the core, stiff plates were placed above and below the layup and the entire assembly was sealed with vacuum pressure
Bends were created in the panels by removing the carbon laminate layer on the inner side of the bend. Some of the Nomex core was removed to allow the panel freedom to bend. The open cut was then filled with a lightweight epoxy, bent to the appropriate geometry and held to cure. Several layers of plainweave carbon fiber cloth were added to inner side of the bend to add strength.
Stanford's Solar Car Sundae
Stanford's team had an extensive use of sandwich panels in their monocoque design. They were able to mount their leading arm, front shock, upper control arm, rear shock brace, trailing arm, steering bell crank, steering column, topshell, canopy linkages. To begin, they created an extensive report on the Tensile Testing of Threaded Bushings in Sandwich Panels in 2017 in order to better understand design choices for load chassis inserts. They determined the maximum loading configurations to guide the design of chassis connections.
They also performed FEA on the key mounting points to determine the loads in the x, y and z directions.
Additional Resources
https://www.fpl.fs.fed.us/documnts/fplr/fplr1574.pdf
Composites simulation resources: