This thesis describes an analytical and experimental investigation into the energy absorption performance of textile-based load limiting devices. The primary technology considered is the stitch ripping device (SRD). Development of analytical models for predicting SRD behavior is presented. The models account for energy absorption due to webbing stretch, thread rupture and stitch slippage. The models predict the force-displacement behavior of the device, the total amount of energy absorption, and the amount of absorption due to frictional losses from stitch slip. Experimental testing conducted to validate model results exhibits close agreement for the applied load and displacement required to induce thread rupture. Over multiple stitch breaks, the models slightly over estimate the amount of absorbed energy. It is predicted that a lower amount of stitch slip decreases activation force as well as fluctuation of force in the plateau region of the force-displacement curve. Decreasing slip increases the amount of energy that can be absorbed for a given peak force and stroke distance. In addition, the effectiveness of adhesive treatments in preventing stitch slippage and pull-out, and the role of stitch pattern and stitch density on energy absorption are examined. Results indicate that certain adhesive treatments increase total energy absorption and reduce stitch pull-out. However, decreases in specific energy absorption result due to increases in total mass from the addition of adhesive. Hand-stitched thread tests show that altering stitch pattern and reducing pull-out increase rip force and energy absorption by 23% and 16%, respectively. Finally, to assess the performance of SRDs under simulated crash conditions, an instrumented dynamic drop rig was constructed. Tests were conducted with a drop sled moving at free-fall velocity, and a higher, elastic-cord-assisted velocity. For velocities from quasi-static to 6 m/s, no significant trends or changes in SRD average activation force and energy absorption were observed in the experiments.

The ideal system for catching a fall while putting a cap on the peak force the anchor experiences is, oddly enough, a static line rope used with a screamer. The elastic aspect of a dynamic rope stores energy and allows you to fall farther than you would otherwise. The rope also absorbs lots of energy, but not as efficiently as a screamer.

Of course you're not going to use a screamer at every single anchor point, but it is an interesting piece of info to store away for a rainy day situation.

No really. That IS NOT the ideal system. What do you think happens when the screamer gets fully deployed? THIS IS DANGEROUS.

The rope also absorbs lots of energy, but not as efficiently as a screamer.

To my knowledge there not a whole lot of evidence, research or otherwise that screamers are an effective tool to protect marginal placements.

Their energy absorbing capacity is very small compared to the climbing rope. Thus their benefit is debatable.

There is a relevant new blog post on Black Diamond's site: http://www.blackdiamondequipment.com/...ot-to-screamer-en-gb

In this test, the peak load was reduced with 1.6 kN or up to 25% with a screamer.

I can personally testify to their benefit in marginal free climbing protection. I've gone through dozens of them in free climbing falls in the kind of Edisonian research that counts. I've ripped them partially and completely. I razor blade them down at a varying angles to adjust their initial loading to suit the placements and sport tape partially blown ones back together for multiple goes. They are absolutely key to marginal pro. I've taken many multiple dives onto nests of RPs / Crack N Ups / #1-3 Loweballs that would never hold a fall otherwise.

None of that is evidence of the screamers being effective. Climbers at Arapiles, the birthplace of RPs, regularly fall on RPs without screamers. I've seen plenty of small RPs hold falls with no screamers.

Ball nuts are rated quite highly and don't need screamers. #2 & #3 are rated at 8kN so are pretty damn strong.

We'll have to agree to disagree then....

Its not that I distrust you or your experience it is just that I trust science more.

We'll have to agree to disagree then....

Its not that I distrust you or your experience it is just that I trust science more.

xxxx are rated quite highly and don't need screamers

Time perhaps for one of the manufacturers to step up to the plate?

It is obvious that a screamer set to say 1,5kN is going to be good for a short fall on your marginal pieces but it will have to be hundreds of metres long to catch that giant whipper.

The issue is how 'smoothly' (fast) you go from 0k to whatever the screamer's rating is.

Do you think that a DMM Revolver on the rope end of a screamer would help with this issue ? The reduced friction would allow some more active rope into the system and the loading curve should be flatter.

To be honest, I don't know and would have to think about that proposition. Plausible in the prelude, but sooner or later I think you're still going to hit that jarring activation bump on the screamer which is why I pre-slice them to smooth that bump out.

Hmm, the noise you may have heard was either Isaac Newton having a rotate in his grave or another school physics teacher killing himself after realising he wasted his life.

Cool with me, but climbing isn't about 'science' and science is both worthless and pointless once you leave the ground.

Climbing has never relied on science and I personally hope it never will - it has always taken an Edisonian approach to sorting out what works and what doesn't.

In every placement I make I evaluate the vector forces and the material strengths base on my understanding of material properties and behavior. I don't pull out my calculator on the cliff face but I certainly do the assessment.

I'm not sure what your view of science is but it seems to be highly distorted.

No science or engineering is required to climb and or evaluate the vector forces which is why you don't pull out your calculator.


Not at all, climbing just never has and never will require it. In fact, given it ain't rocket 'science', if you aren't capable of sorting it all out with basic logic, common sense, and intuition you probably shouldn't leave the ground.

I think I got that - a diagram would help.

In general I'm looking for a screamer on a small, marginal free climbing placement to start ripping at about .25 kn and build up more gradually than a stock one to whatever its rating is.

Nylon ropes? Helmets that deserve the name? Anchoring in while belaying?

all theese are advances that were NOT due to common sense or intuition.

As I explained, its GOT to start at above 1,6kN or so or it isn´t funtioning in any way at all, in fact you couldn´t rest on it.

Exactly, I don't want to be able rest on the screamer - that's why I steeply slice them with a razor blade. What I want is for the screamer to start coming apart at about 20-30lbs and ramp up 'gracefully' to the full screamer rating over about a 3" distance.

The fact that a BD engineer considers fall factor to be a valid variable for testing screamers indicates a serious misunderstanding of the principles involved.

Why on earth would you want a screamer to start coming apart at 20-30lbs? What is the benefit of a graceful ramp up in force? Do you have any evidence that a graceful ramp up in force is preferable?

Well I think we are just going to have to agree to disagree.

However I do wonder what you mean by "equalize cleanly"?

Also I'm just curious. When you say RPs, do you actually mean RP branded nuts?

Nylon was an advancement of science, rope making actually has evolved in a very Edisonian manner driven by common sense and intuition.

And no science or engineering has ever been required for anchoring.

No science or engineering is required to climb and or evaluate the vector forces which is why you don't pull out your calculator.


Not at all, climbing just never has and never will require it. In fact, given it ain't rocket 'science', if you aren't capable of sorting it all out with basic logic, common sense, and intuition you probably shouldn't leave the ground.

I would argue that the problems with the ADT were discovered through a scientific analysis, it certainly isn't trivial the forces involved

Just to reiterate Jim's point, there is no "jarring activation bump" in screamer activation. The load felt by the screamer is due to tension in the rope, which builds up continuously as the rope stretches.

I would argue that the problems with the ADT were discovered through a scientific analysis, it certainly isn't trivial the forces involved

ADT, meaning American Death Triangle? Ignoring friction, it's a high-school physics problem.

Jay