Expansion rate of Carbon Fiber vs Steel

In summary, an auto body technician is considering installing a Carbon Fiber roof on a Volkswagen bug for a customer. They are confident in their ability to fabricate an inner frame and bond it securely, but are concerned about blending the paint into the carbon fiber and potential expansion rate differences between the materials. They suggest using the coefficients of thermal expansion to calculate the expansion and potentially creating a groove feature to accommodate it. The technician is unsure if this is something they can handle or if they should avoid the idea altogether.
  • #1
Valhalla14
3
0
I am a lisc. Auto body tech, and I have a customer who wants a Carbon Fiber roof on a Volkwagen bug, I can fabricate a inner frame, and bonding will not be an issue, (according to paint rep)

The hard part is I want to do a flush seem and have paint blend into carbon fiber. I will "butt" match it, and have it bonded on the back side where I can strengthen the bond, and on the outside I will do the standard procedure as a quarter panel

If the expansion rate is different I will experience cracking, maybe ghosting from the seam.

Is this something I could figure out, or just run from the Idea
 
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  • #2
Yes, you could figure this out with the coefficients of thermal expansion of both materials:

Net Growth = (coeff exp metal - coeff exp carbon fiber) X Temperature Difference X Original Length

The temperature difference would be the maximum or minimum temperature in the area minus the temperature during assembly.

After you figure the expansion, you may be able to put a groove feature or something to accommodate this expansion.
 

Related to Expansion rate of Carbon Fiber vs Steel

1. What is the expansion rate of carbon fiber compared to steel?

The expansion rate of carbon fiber is significantly lower than that of steel. Carbon fiber has a coefficient of thermal expansion (CTE) of around 1.1-2.4 x 10^-6 m/mK, while steel has a CTE of 10-12 x 10^-6 m/mK. This means that carbon fiber expands much less than steel when exposed to changes in temperature.

2. Why is the expansion rate of carbon fiber lower than steel?

Carbon fiber is made up of thin, tightly woven carbon strands, which are held together by a matrix of polymer resin. This structure makes it much more resistant to thermal expansion than steel, which is made up of larger, more loosely bound atoms. Additionally, carbon fiber is able to dissipate heat more efficiently, reducing the effect of temperature changes on its expansion rate.

3. How does the expansion rate of carbon fiber affect its performance?

The low expansion rate of carbon fiber makes it an ideal material for applications that require high strength and stiffness while maintaining dimensional stability, such as in aerospace and automotive industries. Its ability to maintain its shape and dimensions under varying temperatures is also important in precision engineering and high-performance sports equipment.

4. Does the expansion rate of carbon fiber vary with different types of carbon fiber?

Yes, the expansion rate of carbon fiber can vary depending on the type of carbon fiber used. Different types of carbon fiber have varying densities, weaves, and resin matrices, which can affect their CTE. Generally, carbon fibers with higher modulus (greater stiffness) and higher density will have a lower CTE.

5. Are there any factors that can affect the expansion rate of carbon fiber?

Yes, the expansion rate of carbon fiber can be affected by factors such as the direction of the fibers, the temperature range, and the presence of any impurities or defects in the material. Additionally, the expansion rate can also be influenced by the type and quality of the resin used in the carbon fiber composite.

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