The aerodynamic shell of our pod is a rather complex part, made of several double curved surfaces. Manufacturing this part is a challenging process. To allow the fabrics to form properly in the (complex) shape of the mold, the aerodynamic shell is produced by a manufacturing process called vacuum infusion.
In vacuum infusion, several layers of dry carbon fibers are laid up in a shaped mold. A high-strength resin system is infused by vacuum into the fabrics. For this process, we chose the EPIKOTE™ Resin MGS RIMR035c set provided by Hexion, which provides high mechanical properties and results into a low weight structure. The infusion process is performed in a large oven, at relatively high temperature. This is required to achieve the ultimate glass transition temperature of the resin system, allowing for a remarkable improvement of the mechanical properties in the heat of the California sun.
Before the day of the competition, our team must pass a series of more than 100 tests in order to qualify for the final run. Despite the extensive modelling and testing performed on all composite elements of the structure, there is the small chance that the carbon fiber parts of the pod will get damaged during transportation or during testing. In fact, delamination is a rather high risk in proximity of the bolted joints. A risk that our team can easily mitigate; thanks to another system EPIKOTE™ Resin MGS LR 635 set provided by Hexion, we are able to repair a wide variety of possible damages of the structure by performing wet layup processes.
During wet layup, dry sheets of carbon fabrics are laid in proximity of the damaged area. Then, a paint roll is used to apply the resin system over the dry fabrics. The resin system is a two components system coming along by as resin and hardener. These two components chemically react with each other. Allowing the resin system to first impregnate the dry carbon fabrics, then solidify/ partly cures at room temperature and finally can be cured at elevated temperatures if required to achieve the desired mechanical properties.
Composite parts typically need to be cured at high temperatures. However, in the United States, we will not have the possibility to easily reach a large oven within the tight time-frame. For this reason, with the expertise provided by the Hexion engineers, we have selected a resin system which cures at room temperature allowing us to quickly resolve any unforeseen damage and perform at best on the day of the competition!