carbon fiber vs aluminum—panels

Let's say I've got a 1/8" thick piece of aluminum and a 1/8" thick piece of carbon fiber. How does their strength compare? Obviously the aluminum will bend better, but does the carbon resist more abuse before failing?

I used to worry about carbon fiber fatigue resistance until I read that it resists fatigue better than steel. I don't remember any of the details to back that up. And steel does not equal aluminum. Sorry.

CF does resist bending better than aluminum but when it breaks it breaks big time. As with so many things, it all depends on what you are using it for. FWIW, I found in my R/C daze that they have similar abrasion resistance assuming the same material is abrading them. I used to make little Lexan skid plates to protect the 'bend' in my RC10 chassis for that reason.

"Strength" can mean a lot of different things.

In an article on this at The Difference Between Aluminum and Carbon Fiber they say:

Carbon fiber compared to aluminum does degrade quicker as the temperature gets hotter. Carbon fiber of top quality with a good sealant resin may not absorb water. Carbon fiber can oxidize and loose strength due to absorption. The oxidation level increases with temperature, and also with chemical contaminants. Carbon fiber is not as durable as aluminum. Carbon fiber is unpredictable, as analysis and failure results are not as controlled as they are in the case of aluminum. Carbon fiber shatters, and may crack or chip. Aluminum versus carbon fiber is cheaper, but carbon fiber is tensile and not ductile. Aluminum, on the other hand, is ductile, and bends easily.

Read more: Difference Between Aluminum and Carbon Fiber | Difference Between | Aluminum vs Carbon Fiber http://www.differencebetween.net/object/difference-between-aluminum-and-carbon-fiber/#ixzz3V7kDGdLG

So put simply...it depends on the attribute.

Another more important question involves the strand orientation during the layup process. Carbon is one of those really cool materials that allows you to tailor its strengths and weakness to your benefit. For instance you can orient the strands to allow a material to flex for millions of cycles (Think the new Boeing 787 airplane wing) or be extremely rigid (think cf bike frame). I used to do a lot of sailboat racing where carbon fiber is used everywhere. The only time unpredictable failures happened was when either UV reached the material, or it was scratched to the point of exposing the strands. At that point, failures can indeed be spectacular. So, I guess without seeing your application and the layup of the sheet, it is really impossible to speculate. Both yes and no could be the correct answers.

Curmudgeon wrote: CF does resist bending better than aluminum but when it breaks it breaks big time. As with so many things, it all depends on what you are using it for. FWIW, I found in my R/C daze that they have similar abrasion resistance assuming the same material is abrading them. I used to make little Lexan skid plates to protect the 'bend' in my RC10 chassis for that reason.

I remember a test one of the bike magazines did where they were cyclically loading handlebars to failure. (Aluminum bars also fail catastrophically) A lot of the aluminum bars went in the thousands of loadings before they failed. They turned off the machine after the plastic handlebars went a million cycles.

I'm not much of a fan of carbon fiber, but it does have its advantages.

JG Pasterjak wrote: Let's say I've got a 1/8" thick piece of aluminum and a 1/8" thick piece of carbon fiber. How does their strength compare? Obviously the aluminum will bend better, but does the carbon resist more abuse before failing?

What is the application? How do you define "abuse"?

There are many different alloys and heat treatments of Aluminum, and many different kinds of carbon fiber laminate.

Some general material properties:

The elongation (ability to stretch before breaking) of Al is about 10X that of carbon fiber (~1.5% vs 15% strain). But CF is more stiff (at least if fibers are aligned with loading).

A good layman's explanation: http://calfeedesign.com/tech-papers/technical-white-paper/ . CF is used where deformation can be limited, and strength-to-weight or stiffness-to-weight is paramount. It can also absorb a lot of energy, which is useful as a crash structure. http://www.rmi.org/RFGraph-Advanced_composite_energy_absorption_vs_other_materials

Depends

You need to be more specific

Aluminum also suffers from work hardening for every flex, right up until breaking. Steel and carbon fiber both have a bit of elastic flex that does not harden the material, which is why they can be used to make springs that operate in that area of flex. If your application requires or allows flex eventually aluminum will fail.

Thanks guys. Exactly the kind of info I'm looking for. The reality was I didn't know enough to ask the question properly, but those links and charts are heading me in the right direction.

As far as panels, for bodywork at least, I'd rather have bending aluminum than "break into a million shards of razor blades" Carbon Fiber....