Expansion rate of Carbon Fiber vs Steel

AI Thread Summary
A licensed auto body technician is exploring the feasibility of installing a carbon fiber roof on a Volkswagen Bug, focusing on achieving a flush seam with paint blending into the carbon fiber. The technician plans to fabricate an inner frame and bond the carbon fiber on the backside for added strength, while applying standard procedures similar to those used for a quarter panel. A critical concern is the differing thermal expansion rates between the metal and carbon fiber, which could lead to cracking or ghosting at the seam. To address this, the technician is advised to calculate the net growth using the coefficients of thermal expansion for both materials and the temperature difference during assembly. This analysis may allow for design adjustments, such as incorporating a groove feature to accommodate expansion and prevent issues.
Valhalla14
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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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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.
 

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