Carbon Fiber Monocoque Chassis Layup

As a chassis engineer for RIT Racing, I built a Carbon Fiber monocoque chassis. This involved manufacturing and sealing the plugs, infusing the CFRP female molds, and laying up the actual chassis. To make the chassis, we laid up prepreg carbon onto the interior surface of the mold. That means that the first layer we placed down is the exterior, and we worked inward. We laid up an outer skin, cured it, then placed core, and inner skin. The most difficult part of this is the time constraint. Prepreg carbon will start to cure when exposed to room temperature. This means that we had to finish each step within a day or two to mitigate those effects. 

After the creases between the molds were sealed with tape, and releasing agent was applied to the surface. This stops the carbon from curing to the mold. After the release agent cured, we started the first layer of carbon. This was the most important, as it is the visible layer.

Interior of sealed molds with releasing agent being applied. 

First Layer being applied.

First layer completed. 

 We laid down layers according to the layup schedule. The layup schedule is a document containing the order and direction to lay down carbon for each region of the car. 

Example layup schedule, showing region, estimated weight, area. 

After the outer skin is laid up, we sealed the entire thing in a vacuum bag, and send it to be cured at an autoclave. 

Completed outer skin. Notice Unidirectional carbon applied in different directions.

Bagged mold and outer skin. 

Now, the core. For this layup, we used aluminum honeycomb for core. We first cut the core to the correct shapes and gave them initial bends. We then laid down film adhesive, which bonds the carbon to the core. 

First layer of film adhesive. 

The core then is applied on top of the film adhesive. Each region of the chassis has its own layer of core, and the thickness of the core varies by region. Between the different pieces of core we applied expanding foam adhesive, which expands during cure to bond the different pieces of core together. We also inserted hardpoints into the core where suspension and other mounts exist. 

Partial Core application. the weights are used to temporarily hold the core in place. The hardpoints are the black blocks inserted into the core. 

After core is complete, we applied a second layer of film adhesive, and begin placing down the inner skin of carbon. This skin is applied exactly the same as the outer skin, except that the surface is no longer smooth. This greatly increased the difficulty, as the carbon is a flat sheet and did not want to stretch to fit the many curves. After the inner carbon was applied, we applied another vacuum bag and cured a second time in an autoclave. 

Cured Chassis

The resulting chassis then had to be trimmed to size, sanded, and painted. Holes for all the components also had to be located using jigs and drilled. The now complete chassis was handed off to other groups to mount all there components to. 

Finished Chassis

Disclaimer: For simplicity, I have skipped a few steps in the process. Feel free to contact me for questions.