look majid, apparently you don't understand what i'm saying...

you said:


first, you DID use two different knots, but said you didn't.

you don't recognize that the cord FAILED when it streched into the plastic zone. research "plastic deformation."


i'm happy for you. you have an interesting misconception of what you've done.

Thanks - that was a good contribution!

I would not call it definative research due to small sample size and controls, but good preliminary research - creates questions to answer.

Maybe the questions are answered elsewhere.

I was very interested in test 3 with the webbing "doubled". I could not see what you did, nor has it been explained. Was the webbing padded at the bolt by the tail of the knot, or did you do an all around pass if the hanger ?(kind of like how extendable cam slings are attached)

If you did an allaround pass, and it is actually stronger (more research needed) it may be a good tool to apply to tat rappel stations (assuming there is a solid metal rappel ring/mailon for the rope).

Not sure what the effect of that all around pass would be over time - would it resist abrasion from being held in place to the hanger more tightly, or become more abraded because wear is focused in a more specific place ...

More questions than answers - which is where knowledge grows.

B

In some ways, I agree with you, hardman, but in this case, the knots really don't matter. Both the webbing and the cord broke at the bend around the hanger, NOT at the knot. So long as the knot was not the weak point in the chain, it shouldn't really effect the test results.

What bugs me about this test is that it seems to suggest that webbing is better to tie through hangers than cord. After all, the test shows that the webbing tested out stronger than the cord, right? Well, 1" tubular webbing is rated to about 4000lbs whereas 6mm cord is rated to only about 1500lbs. A CONTROL test would have been very useful in adding to these limited test results. Still, if we just use the rated strengths of the materials, we can presume the following: Webbing tied directly onto a bolt hanger will lose a significantly greater percentage of its strength than perlon cord.

In all cases, the overshadowing moral of the story is obvious: Cord and webbing tied directly through bolt hangers lose a significant amount of their strength.

So from looking at the numbers, my conclusion is that 1 inch webbing breaks under a higher load than 6mm accessory cord.

Yes, cord that is rated to 4,000 lbs might break at a higher force than webbing rated to 4,000 lbs, but we call cord that is rated for 4,000 lbs a single lead line. Even 8mm accessory cord is only rated to 14kn which according to my calculations is equal to 3,150 lbs.

I am drawing my conclusion based on the amount of load that it took to break the materials.

What I don't understand (and I think several others as well) is why you (majid) are saying that the cord is a better choice when it took less weight (force) to break it.

So far the only answer that I can find from you on this is that because it fails more gradually, and because if fails gradually you will have time to know what's going on instead of being suprised by the webbing snapping. (that's not that good of a reason to use cord though IMO because you're not going to be able to see your anchor when your rapping and so I would rather have the strongest material possible.

IMO, this is suggesting that even small amount of internal stretch within the material could reduce the impact

We can’t compare a 6 mm cord to 1 inch webbing cause they are not rated the same

3X stretch (at 500-800 fewer pounds of force) is NOT a SMALL AMOUNT of internal stretch. a small amount of internal stretch would be something in the ELASTIC DEFORMATION range (see the stress/strain curve i sent you above). once you reach PLASTIC deformation, the material has failed.

its like pulling a piece of chewing gum out of your mouth, and pulling it apart 12 inches. then concluding the gum is absorbing the load gradually. the gum has already failed. you can DECREASE the amount of force on it, and it will continue to deform until it fractures.

do you understand this concept? i've brought it up several times, and you have not addressed it.

by the way, if i had the personal choice of using 8 mm nylon cord vs 1"webbing, i'd use the cord, even without the test. but i would use 1" webbing over 6 mm cord, because of your test results. so the test you've done is not without value.

what are your reasons behind choosing cord vs. webbing ( if it is going to be used on bolt hanger)

would you please acknowledge that you have some understanding of plastic deformation? please?

would you please acknowledge that you have some understanding of plastic deformation? please?

We can’t compare a 6 mm cord to 1 inch webbing cause they are not rated the same and the reason why we used 6 mm cord is because someone mentioned in ST and we decided to go with that.

Now, after what I saw from this test, I am convinced that If I had to do choose between building an anchor from two separate material meaning on is going to be standard one inch webbing which is rated to 4000+- lbs and let’s say another material like cord/rope which is also rated to 4000 lbs, I am going to pick cord vs. webbing cause IMO under shock load, I think cord handles the load better than webbing but we just have to do a test to find out.

hardman -- is there any chance we could get you to address these issues though PM with majid instead of tainting this otherwise intriguing thread. rc.com has enough of a problem producing useful threads as it is w/o having every other post containing some distracting personal issue you have with majid and this test. thank you.

I think your logic is flawed.

You should prefer cord because it will likely resist cutting by the bolt hanger better than the webbing.

Your test suggests that cord is much less susceptible to weakening over a sharp edge than webbing. In your test, the cord lost less than 50% of its rated strength whereas the webbing lost almost 75% of its rated strength (assuming no strength loss to the knots, which is acceptable since none of the tests broke at the knot).

Now if we assume this is true and the % strength loss to a bolt hanger is the same as with 6mm cord, 8mm cord (at 3100lbs) should out-test the webbing every time. Granted, because the relative radii of the hanger edge to the cord diameter is not the same as with 6mm cord, I would be willing to bet that there will be a greater % strength loss with 8mm cord than with 6mm cord. Still, I would bet that the 8mm cord would out-test the webbing.

On top of all of this, I would be curious as to how 5.5mm spectra cord would perform in the test.

is this turning in to interrogation of some sort ?

Do you want to put this 5.5 mm Spectra on the bolt hanger again or no just pull end to end ?

Make some suggestions for future work and turning out future numbers that are more robust, rather than slogging what has already been done and fixating on what holes exist in this impromptu and on-the-fly test.

you should not have stated what you THINK will happen (but did not test) in your CONCLUSIONS. you have NO BASIS for doing so.

Silascl -- the 'conclusions' proferred with majid's study simply state that:

a) running cord or webbing through a bolt hangar is a bad idea

b) it was noted that the 6mm cord was weaker in breaking strength than the webbing

and c) 6mm cord failed gradually when under stress, unlike webbing which suddenly cut when under stress.

What exactly 'makes no sense' regarding his conclusions, as you have stated?

In regards to accepting the study at face value, majid made of point of asking for comments and suggestions for a future test (which was included in his 'conclusions')-- and has been responsive to requests for different materials and setups, as well as for repeated testing to give results of higher confidence. What exactly are we being forced to swallow here? Do you have any suggestions for future work?

(Opinion) Some people appear to have taken issue with the fact that majid said he would make use or cord instead of webbing if one of the two materials had to be fixed to a hangar. I imagine he reached this conclusion due to the different methods by which the cord and webbing fail under stress (gradual vs. sudden), and not so much based on the absolute strength ratings arrived at by the test.

hardman -- I'm a practicing scientist myself, but there's a difference between being inquisitive and questioning the integrity of someone's conclusion and being an annoying devil's advocate or a nitpicky patty, which I feel is the role you have assumed. Make some suggestions for future work and turning out future numbers that are more robust, rather than slogging what has already been done and fixating on what holes exist in this impromptu and on-the-fly test.