Fulk said:Hmmm . . . we seem to agree that the 7-mm MRs weigh ~60 g, but my krabs seem to be significantly heavier ? at ~55 g ? than the others mentioned here.
Fulk said:Thank you, Mike, but I think that I managed to work that out for myself; I was merely making an observation.
No problem ? but thanks for apologising.Apologies for being patronising -- I was thrown off by the way your comment was phrased. :-[
mikem said:7kN was I believe the 1 inch tubular sling, others failed at lower loading, but it didn't say whether drop tests (I assume it was) or steadily increasing loads..
Chocolate fireguard said:mikem said:7kN was I believe the 1 inch tubular sling, others failed at lower loading, but it didn't say whether drop tests (I assume it was) or steadily increasing loads..
I know quite a few people who believe that a (say) 7kN load during a drop test is more likely to break something than a steady 7kN load, but I have yet to hear what I consider to be a convincing explanation of why that should be.
I'm not saying it isn't so - it's just that almost all of the explanations seem to concentrate on the fact that the load is there for a shorter time (it's "impulsive"), without any attempt to say why a load that is there for only a short time should be more damaging than the same load present for longer!
Now, if I heard someone say that some things (like knots?) often show obvious signs of melting at the failure point, and that in a slow steady pull more of the heat generated when the knot tightens escapes, then I might be convinced.
But I can't see that being a big consideration when a sling fails over an edge.
Topimo said:Chocolate fireguard said:mikem said:7kN was I believe the 1 inch tubular sling, others failed at lower loading, but it didn't say whether drop tests (I assume it was) or steadily increasing loads..
I know quite a few people who believe that a (say) 7kN load during a drop test is more likely to break something than a steady 7kN load, but I have yet to hear what I consider to be a convincing explanation of why that should be.
I'm not saying it isn't so - it's just that almost all of the explanations seem to concentrate on the fact that the load is there for a shorter time (it's "impulsive"), without any attempt to say why a load that is there for only a short time should be more damaging than the same load present for longer!
Now, if I heard someone say that some things (like knots?) often show obvious signs of melting at the failure point, and that in a slow steady pull more of the heat generated when the knot tightens escapes, then I might be convinced.
But I can't see that being a big consideration when a sling fails over an edge.
Rate of energy dissipation - the material has to deform and convert the kinetic energy into heat which is transferred to the environment and elastic potential energy stored in the material itself, load rates are very important with viscoelastic materials (such as UHMWPE - Dyneema). Load it gradually and the material has time to allow the hydrocarbon chains to align themselves with the tension. Load it rapidly and the stress in the material will be higher, breaking these Van der Waals bonds causing macroscale defects - i.e. cracks, tears, failure.
I remember at school bending bars of McCowan's Highland Toffee slowly (and eventually stretching them out), but you could still snap them if you moved your hand quickly enough. Are the two issues related perchance? As in there's a threshold velocity that suddenly overcomes structural stability?Chocolate fireguard said:I know quite a few people who believe that a (say) 7kN load during a drop test is more likely to break something than a steady 7kN load, but I have yet to hear what I consider to be a convincing explanation of why that should be.
Ian Ball said:screw link every time