Is it possible to reshape the CFRP?

[Mito]

If the main cell had an impact which deformed it, does anyone think it could be heated to soften it and then re shaped?

Looking at the factory video of the construction it seems they layer the carbon plastic sheets and then heat and press them together. Presumably we are just dealing with a plastic here which should become malleable when heated as it was when it was shaped.

Does anyone know the name of the actual plastic used?

 

[alohart]

I have always assumed that the CFRP is cured like epoxy or fiberglass which cannot be softened by heat afterward. If true, it could not be reshaped if it is deformed. In fact, it would probably crack rather than deform. BMW seems to require replacement of damaged CFRP, probably because its strength and integrity could not be assured after its carbon fibers are damaged.

 

[jadnashuanh]

When designing a CFRP structure, you have the ability to determine how flexible it is, and how strong it is. For the main structure of the i3, if you bent it beyond its natural limits, you'd be breaking and delaminating the fibers...IOW, it is toast. But, as long as you don't exceed that limit, it will spring back to its original shape. Once exceeded, there is no reliable cure except replacement. It does not become malleable when heated. The epoxy cures, and you can't reliably reshape the thing once that has occurred, at least by bending it. You could add reinforcement layers to it, sort of like a splint, but that would need to be strong enough to replace the existing structure which is why, at least on the i3, they cut out the damaged section and bond in a new one.

 

[Bawareca]

There are factory approved procedures to repair the "live module" and the "drive module" BMW sell the complete side panel, but it doesnt make sense to repair it from economical point of view. Repairing some parts of the aluminum frame could be done, but i guess most insurance companies will prefer to total the car than deal with such a repairs.

 

[Mito]

How do you know the carbon fibre is epoxy based?
I think the sections are maybe glued together with epoxy but other than that it looks like a thermoplastic sheet with carbon fibres running through it. From what I can see the manufacturing process just laminates multi layers together with heat. If the fibres remain intact and it is a thermo plastic it should be able to be heated and bent around theoretically.

 

[Bawareca]

Watch one Formula 1 race and see what happens when the spoilers or the monocok gets damaged.

 

[bwilson4web]

. . .
How do you know the carbon fibre is epoxy based?

BMW told us via advertisements, articles, and SAE papers.

. . .
I think the sections are maybe glued together with epoxy but other than that it looks like a thermoplastic sheet with carbon fibres running through it. From what I can see the manufacturing process just laminates multi layers together with heat. If the fibres remain intact and it is a thermo plastic it should be able to be heated and bent around theoretically.

Your car, let us know how the experiment works out. Perhaps you might use eBay and buy parts from a crashed BMW i3 and experiment on them.

Bob Wilson

 

[jadnashuanh]

Thermal forming verses thermal activated reactions are two very different things. one is essentially reversible, the other is permanent. It wouldn't make any sense to me to make your car frame become flexible with heat. Sitting in the hot sun, with the weight of things, it would start to bend, and not recover. Too much heat, and you'll damage the plastics involved or compromise the structure. Once you delaminate (by exceeding the strength and ability to recover), a CFRP component is damaged beyond repair verses just returning to essentially as new. A thermal forming plastic, when a force is applied can still flow, it just flows better when it is warmer - and, big thing here, it does not flow back to its original shape unless you're really lucky. When bonded together, the CF is very strong, and you can adjust the properties by how the fibers are aligned and the number of layers. Some companies make CF springs, that obviously are more flexible than our car's frame. It all depends on how you put it together.

 

[Mito]

I lifted the sill cover to expose a part of the floor where the side section is lapped over the floor and tried to cut a small section of the excess carbon fibre material off with a single edged blade. The first thing I noticed was that it was really hard and unlike a plastic to cut and it just powered when pressed into with a blade. It was not possible to just slice a chunk off to experiment on so I can on,u assume this is a " heat cured " type of adhesive despite looking like a thermoplastic. The actual black glue used to bond the two pieces together however was very spongy like polyurethane screen glue or silicone. Altogether a pretty impressive material but I think the shape of it is fixed. I can understand now whey they cut it with water jets to prevent airborne carbon fibre particles entering people's lungs. The actual weave is like a tartan with the major fibres at about 10mm gaps but a much finer material at right angles.

 

[brastic]

The term CFRP and carbon fiber mean the same thing. The quick answer to your question is, "no". The CFRP cannot be molded by heat once built. In order to get the body panel to form correctly, heat and pressure are used. I have built CFRP parts without heat before, but it is a lot harder to do, the parts usually do not form well and are not as strong. Most of the time when I build a car part, I use fiberglass and polyester resin. Mainly because they are cheap, easy to work and are not as dangerous. If I have to use carbon fiber, then epoxy is used. You cannot use polyester resin with carbon fiber. It just does not stick well. The epoxy is also much easier to get into the carbon fiber weave.

The confusing part here is the word, "plastic". There are thousands of different types of plastics and each has its uses.