|
Rob.hack
May 2, 2012, 9:06 PM
Post #1 of 12
(10247 views)
Shortcut
Registered: May 1, 2012
Posts: 14
|
I am interested in conducting drop tests on individual gear placements.
From reading other threads on this forum I believe that the 'fuse' method would be the most suitable.
What I've been unable to find is data on the breaking strength of the knotted cord fuse, ideally in a dynamic setting.
I don't believe the method of doubling the rated strength of the cord and decreasing it by a percentage relative to the knot being used gives a sufficiently accurate figure.
Could anybody comment on this?
Have any empirical tests been conducted to ascertain the breaking strengths of different fuses? Ideally finding setups with a breaking strengths at intervals up to that generated by a 'worst case scenario' fall.
I am looking specifically for studies with suitably large sample sizes so I can determine the range of the breaking strength.
Thank you in advance.
|
|
|
|
|
majid_sabet
May 2, 2012, 10:24 PM
Post #2 of 12
(10210 views)
Shortcut
Registered: Dec 13, 2002
Posts: 8390
|
Rob.hack wrote: I am interested in conducting drop tests on individual gear placements. From reading other threads on this forum I believe that the 'fuse' method would be the most suitable. What I've been unable to find is data on the breaking strength of the knotted cord fuse, ideally in a dynamic setting. I don't believe the method of doubling the rated strength of the cord and decreasing it by a percentage relative to the knot being used gives a sufficiently accurate figure. Could anybody comment on this? Have any empirical tests been conducted to ascertain the breaking strengths of different fuses? Ideally finding setups with a breaking strengths at intervals up to that generated by a 'worst case scenario' fall. I am looking specifically for studies with suitably large sample sizes so I can determine the range of the breaking strength. Thank you in advance.
there is been few test done by tom moyer on knots and many other people but IMO, what we lack the most is drop test on climbing gear such as nut or cams ,jumars, daisy the skinny ass runners and spectra
|
|
|
|
|
Rob.hack
May 2, 2012, 11:18 PM
Post #3 of 12
(10192 views)
Shortcut
Registered: May 1, 2012
Posts: 14
|
Thanks.
My goal is to begin testing gear in a rock face. I believe a lot can be learned from lab tests but also that there are variables that cannot be replicated in a lab setting. To begin testing I need a way of ensuring that I am subjecting the gear to sufficiently high forces.
Specifically I would be testing the pull out strength of placements, rather than their breaking strengths.
I believe that using a shock limiting fuse made of cord would be a better choice than using a dynamometer or other similar device as the initial cost is lower and th setup is lighter and more expendable. That is providing that a fuse can provide a suitable degree of accuracy.
Eventually, when I have a appropriate rig I would like to flm the loading of the pieces in an effort to analyse the physics that they are subjected to at the point of loading.
|
|
|
|
|
USnavy
May 3, 2012, 2:21 AM
Post #4 of 12
(10162 views)
Shortcut
Registered: Nov 6, 2007
Posts: 2667
|
Rob.hack wrote: From reading other threads on this forum I believe that the 'fuse' method would be the most suitable. .
The other issue is that a fuse works to a very limited degree to tell you if a fall exceeded a roundabout value, but it does not really tell you how much force the top piece would have actually experienced in a fall. If you want, I can tell you where you can get a portable load cell analyzer that can be powered off of a laptop and a 5,000 lbs load cell for under $600.
If you look at my thread here:
http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=2574668;sb=post_latest_reply;so=ASC;forum_view=forum_view_collapsed;page=unread#unread
I used the load cell analyzer I am referencing to generate the data in that post.
(This post was edited by USnavy on May 3, 2012, 2:36 AM)
|
|
|
|
|
JimTitt
May 3, 2012, 5:00 AM
Post #5 of 12
(10129 views)
Shortcut
Registered: Aug 7, 2008
Posts: 1002
|
Fuse testing with commercially available cord is worthless, the variation in actual strength to rated strength can easily be 10 to 15%, the variation in the knots about he same and dependong on the knots and materail the difference between static (the rated strength) and dynamic tests around 25%. If you could get an accuracy of 30% that would be good IŽd think.
"I believe a lot can be learned from lab tests but also that there are variables that cannot be replicated in a lab setting"
The variables outdoors are effectively infinite which is why lab tests are done.
Introducing cord into a dynamic system will change the force felt by the piece as the dynamic characteristics of cord is usually different to that of climbing rope.
Drop testing is laborious, slow and expensive. To perform a meaningful number of tests outdoors takes a small army of helpers and a carefully chosen site. We use an powered winch for hoisting the weight for good reason and you need a rope sponsor as well!
|
|
|
|
|
gunkiemike
May 5, 2012, 7:32 PM
Post #6 of 12
(10004 views)
Shortcut
Registered: Oct 1, 2002
Posts: 2266
|
I've done LIMITED testing on fuses made from sewn 1" webbing. My experience, backed up by others with commercial experience sewing life-critical gear, is that the tensile strength of a sewn splice is proportional to the number of stitches. I used ordinary sewing thread, which of course is ridiculously weak compared to what's used for bar tacks and the like. But I was able to demonstrate a remarkably linear relationship between stitches & strength ranging from well under body weight to approx 925 lb. nb - all were based on slow pull testing.
|
|
|
|
|
USnavy
May 6, 2012, 7:19 AM
Post #7 of 12
(9953 views)
Shortcut
Registered: Nov 6, 2007
Posts: 2667
|
gunkiemike wrote: I've done LIMITED testing on fuses made from sewn 1" webbing. My experience, backed up by others with commercial experience sewing life-critical gear, is that the tensile strength of a sewn splice is proportional to the number of stitches. I used ordinary sewing thread, which of course is ridiculously weak compared to what's used for bar tacks and the like. But I was able to demonstrate a remarkably linear relationship between stitches & strength ranging from well under body weight to approx 925 lb. nb - all were based on slow pull testing.
|
|
|
|
|
JimTitt
May 6, 2012, 7:53 AM
Post #8 of 12
(9949 views)
Shortcut
Registered: Aug 7, 2008
Posts: 1002
|
gunkiemike wrote: I've done LIMITED testing on fuses made from sewn 1" webbing. My experience, backed up by others with commercial experience sewing life-critical gear, is that the tensile strength of a sewn splice is proportional to the number of stitches. I used ordinary sewing thread, which of course is ridiculously weak compared to what's used for bar tacks and the like. But I was able to demonstrate a remarkably linear relationship between stitches & strength ranging from well under body weight to approx 925 lb. nb - all were based on slow pull testing.
Bar-tacking is undoubtedly more accurate but it is then a chicken and egg situation. To make the fuses accurately you need a commercial bar-tacker and to calibrate them you need a drop tower and strain guage. Seems a bit of an expensive and roundabout way of achieving a less accurate result than just using the strain guage in the first place.
|
|
|
|
|
gunkiemike
May 6, 2012, 10:15 AM
Post #9 of 12
(9940 views)
Shortcut
Registered: Oct 1, 2002
Posts: 2266
|
USnavy wrote: That is interesting. But the big question is how do you know how many times the thread penetrated through the material?
Easy, I am doing simple straight stitching on a home sewing machine. I count the stitches each time.
|
|
|
|
|
USnavy
May 6, 2012, 10:59 AM
Post #10 of 12
(9936 views)
Shortcut
Registered: Nov 6, 2007
Posts: 2667
|
gunkiemike wrote: USnavy wrote: That is interesting. But the big question is how do you know how many times the thread penetrated through the material? Easy, I am doing simple straight stitching on a home sewing machine. I count the stitches each time.
|
|
|
|
|
cracklover
May 8, 2012, 2:46 PM
Post #11 of 12
(9818 views)
Shortcut
Registered: Nov 14, 2002
Posts: 10162
|
JimTitt wrote: Fuse testing with commercially available cord is worthless, the variation in actual strength to rated strength can easily be 10 to 15%, the variation in the knots about he same and dependong on the knots and materail the difference between static (the rated strength) and dynamic tests around 25%. If you could get an accuracy of 30% that would be good IŽd think.
Interesting.
Anyway, for your purposes, clearly that range is absolutely way too high to be any use. But for my purposes, and other recreational climbers, it can be an effective test.
I wanted to see if my Aliens had a bad braze and would fail at fairly low loads. I was able, unless I'm very much mistaken, to test my Aliens to 4-5 kN. My cords always failed at the same place (where they entered the double-fisherman's knot), which makes me think the variability might be a little less. Of course that spread (20% difference from greatest to least) is way more than would be acceptable for any of your purposes, but it was fine for me. Even if the force got a little higher, I wouldn't damage the piece, and lower, I would still have confidence that it probably was not a defective piece.
It also has the benefit of being cheap, and relatively easy for a recreational climber to do. However, knowing how much of a range there is between tests, I might in the future do two or three tests for a piece I was concerned about.
GO
|
|
|
|
|
gunkiemike
May 16, 2012, 11:00 PM
Post #12 of 12
(9541 views)
Shortcut
Registered: Oct 1, 2002
Posts: 2266
|
USnavy wrote: gunkiemike wrote: USnavy wrote: That is interesting. But the big question is how do you know how many times the thread penetrated through the material? Easy, I am doing simple straight stitching on a home sewing machine. I count the stitches each time. That sounds like a lot of work. When I was doing some highline testing I accidentally stitched a piece of webbing with 50% cotton 50% nylon. I had eight bar tacks that were double backed. There were probably some 750 thread penetrations. Yet the stitching failed at less than 1800 lbs. So it seems if you are using cotton, you need a hell of a lot of tacks to get any worthwhile strength from the webbing.
Not really that hard. I put 185 stitches in the webbing (polyester thread as I recall) in less than a minute. Took another minute to count them. Pull testing broke it at 925 pounds. Results were VERY linear from 8 to 185 stitches when I was doing this. This wasn't for "safety gear" but just to make a fuse for Alien testing. If I wanted something that wouldn't break, sewn aiders for example, I would extrapolate the results and go with 400-500 stitches, minimum.
|
|
|
|
|
|
|
|
|
