In reply to Epic Adventure:
Cheers for the thorough response!
I'll try not to go on too much, because the details of the project are on the website www.crabdev.co.uk but just to try and reply to a few things:
In terms of injection moulded short fibres - new grades and combinations of short random oriented fibre composites are being produced all the time - with modulus and tensile strength approaching that of 7075-T6 but with around half the density. One of the latest, 90HMF40 from Victrex, was released less than a year ago and has a modulus of around 45GPa and UTS of 350MPa, density 1440 kg/m3 (compared to 7075-T6: mod 70, UTS 500, density 2880). As it is it would perhaps be slightly low modulus and might now hold it's shape well enough, but 5-10 years ago we were a lot further away than we are now. Still, I wouldn't discount this material until it's been tested.
The main problems I could think of were: toughness, wear, damage tolerance and damage detection. I looked at some research into improving composite toughness - but it appears using injection moulding of short fibres avoid a lot of the problems (no delamination), but only testing will reveal if the materials are up to it. The other issues will need solutions - for wear perhaps a low friction coating or additive, damage tolerance can only be tackled with testing to find performance (and then improving if necessary), and detection might involve an ultrasound checking service for suspect gear.
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> Whilst in a book you may be able to obtain tensile strenghts of 3 times that of hardened steel in reality you looking at around 70GPa which is acheivable with good alloying.
I'm not sure what you mean here, are you talking about modulus or strength? Carabiner aluminium is roughly 500MPa UTS and 70GPa modulus. I agree that textbook values for UD or multi-axial laminates are not that useful because the crab won't just be pulled in one direction. But short quasi random oriented fibres give very close to isotropic properties.
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> As for open gate crabs - not on my rack thank you!! The flaws are obvious.
I know it's a bit far fetched maybe - but I envisioned a sport crab where the sling is held captive in the quickdraw (like the DMM mamba ie. crab cannot be cross loaded, in this case, understandably, the EN requirements forgoe the need for cross-loading testing) with a skinny flexible gate to prevent the rope from just falling out. You would have to overdesign the body to account for the fact that's it's weaker in the open gate mode, but it might make for a nice smooth clipping crab (though probably not lighter in this case).
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in addtion to this the relative impact forces are low, compared to that of a crab, neither have to sustain heavy abraision, whilst the axes does its not anywhere near as critical and the failure would be detectable.
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I would argue that axes do have to handle heavy abrasion! But you're totally right about the criticality of the crab. And as composites tend to be a lot more rate dependant it might be necessary to have new standards to check their safety in a sudden impact climbing fall (current EN standards require only static pull tests). Apart from that, testing a sample out of every batch in the normal way would still give a good guarantee of consistent strength.
Anyway, if you feel like a reading my (big boring) study on it, it's all online at the website! You'll probably find a lot of it a bit obvious if you're from a composite background, but I was starting from zero knowledge of composites for the project so please forgive the lengthy background info.