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Old 09-10-2013, 02:41 AM   #1513
640 Armageddon
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Joined: Mar 2009
Location: Greece
Oddometer: 2,827
Hi Paul !

Hi Michael,

It is nice to have a discussion about new materials as a lot of people will benefit from that at the end of the day and it is always nice to add to the knowledge pool so don't feel that we regards composites as a no no

I think we are confusing here the impact resistance with penetration resistance.
Penetration resistance is excellent. If you are using Aramid , the more the better. Aramid is used for the bulletproof vests without any resin for example. Indeed its penetration resistance is something out of this world (if used properly).
Think of the F1 cars when crashing around. You can put a grown up man's weight on the front wing but the slightest hit makes it go sky high . The direction of the thing plays also a very important role, as the wing mentioned above is designed to create downforce, not sustain impacts... But it gets complicated when you add factors such as impact to weight ratio.
Impact resistance on the other hand is not as good in composites. Why? Mainly because of the resins. The resin will crack if you hit it with a hammer. Why? Because it is not flexible enough. Polycarbonate for example, has excellent impact resistance, it is used in bulletproof glasses and it is flexible enough to distribute the hit in a larger volume of material if you like. That is what I mean by penetration resistance. Polyethylene the same. It can be bend back to shape.

I made a shell when was gathering data for our roadbook. You could stand on it, no problem. Two men standing on it. Still no problem. Hit it with a hammer and ... boys, we are going in It was a vac part. It is this impact strength that I a worried about. And then again, Polycarbonate, Polyethylene, Aluminium can be simulated relatively easy in a computer to give you a quick idea of what will happen. With composites, it can be done, but it is relatively difficult at the moment. I guess it depends on what you need. By the time I could not penetrate the Aramid with the hammer, the shell was thicker as heavy aluminium

The info that you give on the strands is correct. This for example would be of great benefit in a bash plate. The resin gives up and the sheet stays there until the end of the stage. You do not need rigidity there at all.

My latest r&d is hybrid assemblies. For example you could use thin thermoplastics to gain weight and reinforce them with aluminium plates wherever is needed to achieve rigidity. One could use thin composites and reinforce them with metal plates or use special resins or even use thermoplastic plates to shield them against penetration. Better make something as flexible as you can and keep it as rigid as it needs to be to perform its task. AntiPaul's Polyethylene tower is inspirational in my opinion . The design allows to be rigid in the axis that it needs rigidity and allows to be flexible in the side direction.

Always happy when discussions like these arise here, this is how people move forward

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