Carbon Fiber 101

What Should I Know About Carbon Fiber?

[MJ] There are two ways to create a fiber reinforced laminate; "wet" layup and pre-impregnated fiber layup.

The "wet" layup process has been used since the advent of composites to create molded shapes from glass or carbon fiber and resin. It is the easiest and least labor intensive method available for molding composites parts and is now utilized primarily by do-it-yourselfers to create product without large capital investment. The primary disadvantage of the wet laminate is the lack of resin control.

Dry fiber (glass, carbon, etc.) is laid into the mold and resin is poured and brushed over the cloth in a relatively uncontrolled fashion. Layer upon layer are added and "squeeged" on in this manner until the desired thickness is met. With this uncontrolled resin impregnation, the laminate can be made too resin rich – adding excess weight and reducing overall strength and stiffness. Additionally, without proper attention, areas of the laminate can end up without enough resin, thus creating a high content of voids and subsequently decreasing mechanical properties.

The pre-impregnated (pre-preg) fiber method has been developed over the past two decades to create stiffer, stronger laminates with controllable, predictable results. In this case the fiber is pre-impregnated with resin at a production facility, rolled on spools, and frozen to prevent the resin from curing prematurely. This material is cut and hand laid into a mold to the proper thickness and cured by one of two methods described below. The resulting laminate has a precisely controlled resin volume (+/- 2%) and will be 20-30% stiffer and stronger than an equivalent-thickness wet laminate.

The first method of curing a pre-preg laminate is to put it under vacuum bag compaction and place it in an oven for the prescribed amount of time until the resin "glasses", flows and hardens in the shape of the parent mold.

The second method for curing the pre-preg laminate employs the same vacuum bag compaction as the first, but adds the extra force of the autoclave to "pressure cook" the laminate. In both instances, the cure temperature will also be the maximum allowable temperature of the cured laminate with a continuous service temperature slightly lower. This temperature generally resides between 250 and 350 degrees Fahrenheit.

In the case of the DaliRacing hood, the laminate consists of a lightweight closed-cell core sandwiched by two pre-preg skins. This 250 degree autoclave cured part is manufactured with a process nearly identical to the chassis and bodywork of today’s Formula 1 and Champ Cars with strength and stiffness to match.

Before you buy ANY carbon fiber parts, make sure of what you are getting. After doing my homework I decided that you really get what you pay for in this area.