19 replies to this topic

[Andy!]

Carbon fibre is stronger than steel, so i doubt you'd have any reduction in strength at all, if anything you'd gain strength, one question though.... why? is it an ultra lightweight track machine?? if not, i ask again... why :s

So is spiders silk but you can't make a car from it! CF is brilliant when it is used in the way it is designed to be used. That is very different to how a mini is put together. It would take too long to explain fully but just replacing the A panel would result in a significant loss of strength if done in a like for like fashion. Even with a full structural adhesive such as DP410 the way it would be loaded in a crash is totally wrong. This comes from experience in designing and building CF monocoques for endurance racing. You have to throw away all your steel monocoque knowledge and do it a completely different way. CF A panels are good for looking nice (if you like that sort of thing) and saving weight - hardly relevant on a road car as there are a thousand better ways to save weight.

Ah right, fair enough i hadnt thought about the bonding side of it, i just thought of the 2 materials on their own, good point and nicely explained thanks mate

[Tamworthbay]

Carbon fibre is stronger than steel, so i doubt you'd have any reduction in strength at all, if anything you'd gain strength, one question though.... why? is it an ultra lightweight track machine?? if not, i ask again... why :s

So is spiders silk but you can't make a car from it! CF is brilliant when it is used in the way it is designed to be used. That is very different to how a mini is put together. It would take too long to explain fully but just replacing the A panel would result in a significant loss of strength if done in a like for like fashion. Even with a full structural adhesive such as DP410 the way it would be loaded in a crash is totally wrong. This comes from experience in designing and building CF monocoques for endurance racing. You have to throw away all your steel monocoque knowledge and do it a completely different way. CF A panels are good for looking nice (if you like that sort of thing) and saving weight - hardly relevant on a road car as there are a thousand better ways to save weight.

Ah right, fair enough i hadnt thought about the bonding side of it, i just thought of the 2 materials on their own, good point and nicely explained thanks mate

No problem, I have spent an evening thinking of how it could be done. I feel a project for our work hillclimb special coming on.......

[jakejakejake1]

Everyone who says that carbon fibre doesn't absorb energy, shatters, is weak etc etc is probably going by what they heard on the internet, the fact is to shatter a carbon fibre panel it takes a huge amount of energy. As long as the carbon being used is proper pre-preg stuff, and not the cheap(er) type which is hardly better that plain old fibreglass.
But I agree that most places on a mini are not the correct place for carbon fibre due to the design, I just don't agree with the bad press carbon fibre seems to get about being weak.
Also it doesnt help that most carbon fibre parts for minis are made from the cheaper type, not the proper structural pre-preg which should be used for structural parts on a car.

[Alex_B]

I'm not going by what I have learnt on the Internet I'm a motorsport engineering degree student so I'm going by what is being taught, yes it takes more energy to shatter than other similar composites but it still shatters rather than bends which is how the minimal crash protection on the mini was originally conceived and as such isn't suitable to just swap panels out without any further engineering

[tiger99]

Alex_B, you are absolutely correct. Actually, there is nothing suitable for building cars which is significantly better than the crumpling of ordinary mild steel for absorbing energy safely. No composite comes close, nor do any light alloys.

A composite may work tolerably well, but only if it is designed in such a way that it will progressively shatter into lots of tiny pieces, the bulk of it remaining attached to the car, with bits of the leading edge gradually breaking off. The energy absorbed is proportional to the total length of the fractures, and has a very finite limit. Steel just keeps on crumpling until it is flat, or solid, or whatever its final shape is going to be, absorbing energy all the way.

It follows that a safe composite car will be of very different structural configuration to a safe steel car, and simply replacing a steel panel with a composite panel of the same shape is useless.