Climbing Science: A Study on Carabiner Testing & Strength, Part 1

[Tommy Blackwell]

Good morning guys:

Below is a link to Part 1 of a 3 part series that promises to answer several questions on carabiner strength.

The answer to " How much does rope wear reduce the strength of a carabiner?"   will be of interest to us, as it relates to our Sport Anchors on so many of our routes.

 This first article doesn't answer any questions, it just describes standard testing that  you are already familiar with.

If you already get these articles and dont need me forwarding the links to part 2 and part 3 ( when they come out) , just reply to this email with "stop". 

I know how full an In Box can get with email and I dont want to be stuffing your In Box with extra email.

http://mojagear.com/journal/2015/11/12/climbing-science-a-study-on-carabiner-testing-strength-part-1/?mc_cid=31e2270cae&mc_eid=321ca95fe1

Tommy 

[Vinny]

Tommy, having been to several carabiner manufacturing facilities and getting a good idea of their processes, i think this article is pretty biased to one manufacturer.  Which is fine but...has me questioning its intent.  Its commonplace to test every biner before its sent out but batch testing has shown to be just as effective as the manufacturing processes have come a long way.  I also wonder if its addressing the real issue here...Like the old DMM tests have concluded, strength isnt the issue with a worn biner as much as how rope wear can groove the biner sharp, causing rope damage or even can cut a rope.  Strength when pertaining to fixed hardware is usually more affected by the nylon sling, which can degrade in direct sunlight.

Neil brought in a super old Fixe draco, tested out fine.  We've tested really grooved steel and alum biners here, they tested out fine.  The real test is how it damages a sheath...which the DMM test addresses.

Also, if anyone wants to test an old and worn carabiner, we have a pull tester here at climbtech, bring an six pack and lets break stuff...anytime.  ..

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[Tommy Blackwell]

Thanks Guys!

Vinny, you point out some interesting thoughts to be aware of in Part 2 and 3. Thank you. Those are:

1. Will the point of the article be to recommend a particular manufacturer?

2. Will the testing of grooved carabiners show the strength of the carabiner isn't the issue, but the groove 's damage of the rope sheath is. 

I thought part 1 was brief, and hope that parts 2&3  will have more depth.

Tommy

Sent from my iPad

[Matt M]

I suspect the part 1 tendency to mention BD the most isn't so much a preference bias as it is indicative of which companies have put out the most information regarding testing procedures, outcomes etc etc.  BD has long been the most active in this category with the Kolin Powick QC Lab blog.  DMM has also been contributing information more recently via their "Knowledge" tab on their website.  Beyond those two players, the information density drops off precipitously after that with a smattering of videos from the manufacturers and the occasion article from a climbing blog (usually a visit to a certain brand or a more general post like Tommy linked).  Rope info is pretty much limited to stuff put out by Beal or Mammut but can be challenging to find.  Petzl has a lot of good info out there but it's a PITA to find it on their terribly organized site.  After that, info on sourcing and testing become much harder to locate.  I suspect part of that has to do with the fact that there's a LOT of "sharing" of manufacturing resources amongst the brands and getting into the details of production would muddy the waters when consumers learn that each brand isn't really producing "in house".  There's a fair amount of OEM production with brands simply putting their label on it.

As Vinny points out, worn biner issues are more about sharp edges etc vs loss of strength (which is much more relative in things like 8mm slings and skinny ropes).  It's actually pretty hard to find a truly terrible biner these days.  Where the great stand out from the merely good isn't so much in raw strength but in the "details".  Things like finish quality, open gate strength, nose design and gate shape play a role.  Vinny rightly points out that how a biner wears is also of great importance and some companies do this better than others.  Take a look at a CAMP Photon vs a DMM Spectre 2.  The DMM is vastly superior IMO.  

These days I don't worry so much about testing of ultimate strength.  I worry about the details: 1) Open Gate Strength 2) Nose Design (shielded, notchless etc) 3) cross section profile (will is wear smooth or sharp?)

Curious to see if this series provides any new insights...

[Tommy Blackwell]

Part 2

This is part 2 of a 3-part university study, conducted to assess carabiner strength and testing methods. Part 1 provides background into the studyand addresses prior research, part 2 covers metal gear experimentation and results, and part 3 will explore webbing gear testing approaches and strength.

 

Breaking carabiners test preparation:

With my initial set of background questions answered (see Part 1 of this Carabiner study), I began to formulate my test method as I machined my carabiner testing fixtures. While I was working on my fixtures I also began accumulating old carabiners of all shapes and sizes. I contacted local Search & Rescue groups, climbing gyms, dirtbag friends, and even went as far as taking the oldest and most beat up 'biners from my own rack—which at the time was rather pathetic amalgamation of new and used gear.

The carabiners I was most interested in collecting were those that were extremely rope-worn. Having had climbed for a number of years up to that point, I found that some of my oldest and most heavily used pieces were suffering from wear where the rope abraded constantly in the same place.

The state of my belay carabiner was especially shocking! Such an integral piece of gear as a belay biner should (ideally) be in perfect condition; the excess wear got me wondering if the loss of metal could compromise the strength of the piece. Not to mention the sometime sharp edge that can be produced as a result of extreme rope wear.

So, I sat down at the Instron machine with my box of old carabiners and I began to design my test.

The two main questions I wanted answers to:

Does a carabiner really break at the load (kN) printed on the spine?

 

How significantly (if at all) does moderate rope-wear effect the breaking strength of a carabiner?

 

Machine setup

To answer these questions, testing was conducted using the Cal Poly Mechanical Engineering Department’s Instron model 1331 that has a 100 kN (11 tons) capacity—which is like, Adam Ondrastrong!

The procedure used for breaking a carabiner basically involved loading the carabiner into the fixtures I made, clamping the fixtures into the machine, dialing a few settings, pressing record on a chart (which measured applied strength of the machine on the carabiner versus elongation of the carabiner as it stretched under the given load), and pressing ‘start’ to watch the breakage!

http://youtu.be/x_fTavmDwLw

Results

Non-locking carabiners tested:

Testing began on an assortment of non-locking carabiners all with either wire or solid gates (bent, straight, or key). The first carabiner tested was a new Black Diamond Posiwire. The Posiwire is D-shaped, has a key gate, and has closed gate rating of 25 kN and an open gate rating of 8 kN.

The results from the Single Pull To Failure test (that is the official term for pulling on a 'biner until it explodes) can be seen in the figure below.

Half Dome, is that you?! Load vs. displacement curve for a new Black Diamond key gate carabiner initially closed and put through a Single Pull To Failure test. Highest peak represents failure of gate at 27.9kN; second, small peak on the right represents spine failure at 7.4kN after broken gate.

The linearity of the curve from 0 to 23 kN approximately represents the elastic deformation region of the closed carabiner. Above this range lies the plastic deformation region (where metal has stopped bending and is actually stretching like silly putty).

Failure first occurred at 27.9 kN when the gate exploded, and the spine of the carabiner failed at 7.4 kN. These results show an 11% increase from the printed closed gate rating on the carabiner and an 8% reduction in strength from the open gate rating. This trend was common for all tests done of this type, and shall be explained in detail later in the conclusion section.

Conclusions for non-locking carabiners

When testing non-locking carabiners, two things were generally observed to be constant from every test based on gate type:

- For non-locking wire gate carabiners, failure would typically occur the base of the spine with no initial failure at the gate.

- For non-locking key gate carabiners, the carabiner would fail at the end of the gate due to bending of the key hole.

Granted the rate of pull of the machine, testing was conducted slowly such that the loads could be considered static. This applied static load would first break the gate (for new carabiners, failure always occurred at a load greater than the closed gate rating), and the load would increase until the carabiner would fail at the spine around the open gate rating of the carabiner.

Almost always, the open gate rating would be greater than the applied load to open gate failure. It is important to take note of this discrepancy as it appeared frequently. This is most likely due to the fact that as the carabiner begins to deform before initial failure, it deforms past the point of elastic deformation and begins to permanently deform shortly before failing at the gate. When the gate fails, the plastic deformation serves to weaken the spine such that it breaks at a lesser value than the open gate rating specifies.

Given this hypothesis, it cannot be considered valid to extract two results from one SPTF test in order to compare both the open gate rating and the closed gate rating. Thus, for every test conducted, only the ultimate strength of the closed-gate test could be considered valid.

As an aside to testing the reduction in strength of a carabiner due to rope wear, one particularly interesting test was conducted on a severely corroded bent gate carabiner found on a canyoneering trip in Death Valley. The carabiner was found half buried in dirt and at the time of discovery would not open. With a little cleaning and some oil, it eventually opened and was subsequently used for clipping gear to a backpack before being donated for testing. No amount of cleaning could hide the thick layer of aluminum oxide penetrating the surface of the spine. This Omegalite 3 ‘biner had a closed gate rating of 25 kN and failed at merely 16 kN (still approximately 3,600 lbs)!

Locking carabiners tested:

For locking carabiners, testing was conducted on both new carabiners and old rope-worn carabiners. The hypothesis was that rope worn carabiners would have a significant reduction in strength over their new counterparts, due to the fact that the reduced cross sectional area of the rope worn area would significantly reduce the strength of the carabiner by creating stress concentration in that area. This is the same principle that explains the ease of breaking a wishbone.

Available for the test were two auto-locking belay carabiners, both with approximately 3 mm deep grooves from regular use belaying (see Figure 8). These two carabiners had a closed gate rating of 24 kN and an open gate rating of 8 kN. Both rope worn carabiners responded similarly to the SPTF test and failed within 0.5 kN of each other. The results of the test in graphical form are as follows.

Results of tensile test for locking carabiners. You can see that the distance stretched (displacement) was much greater here than on the non-locking carabiners. Also, the breaking strength of the closed-gate locking carabiner was much higher.

Up next in Part 3, results of tests conducted on textile gear, such as quickdraw dogbones and slings—new and old—will be explored.

Tommy

[Matt Markell]

Interesting Tommy,

Testing of new biner strength looks good and not surprising given their 3 sigma methods.

I wish he has noted WHERE the failure of the highly corroded biner occurred.  Given the older design (pinned solid gate) I’d be curious if it was at the pin/notch interface since that’s where the least amount of material is and where corrosion would take its greatest toll % wise.

His comments about the open gate strength are a bit off or misleading.  The UIAA spec for open gate strength tests a new biner from an open gate position from start to finish.  The strength is not taken after closed gate failure as he does.  I’d hope he knows this but it’s unclear.  His results are actually encouraging given how much force the biner has already been subjected to.  IMO, nearly all modern carabiner are “Good Enough” in the closed gate rating.  The possible exception are the really, really light ones that get down around 20kN closed.  That’s a wee bit light for my greater than UIAA testing weight rear end.  Where I really think ratings matter is the open gate strength.  I prefer 9kN at a minimum and won’t go below 8kN.  Biners do break and much more frequently than we’d probably like to admit.  Open gate loading is more than likely to blame so adding on another kN or two there is worth it to me.  DMM and Petzl agree.  A lot of our Trad gear hovers around the 9kN mark so it’s a reasonable target.

If a placement is mission critical (ie it’s the only thing between you and bodily harm) use a locker of some sort.  Shit happens and biners get loaded open gate (or completely unclip ala that terrible one in Eldo).  I have at least one draw or sling with me with an Edelrid Pure Slider on it.  

M

  

On Nov 19, 2015, at 9:11 PM, Tommy Blackwell <black...@gmail.com> wrote:

Part 2

This is part 2 of a 3-part university study, conducted to assess carabiner strength and testing methods. Part 1 provides background into the studyand addresses prior research, part 2 covers metal gear experimentation and results, and part 3 will explore webbing gear testing approaches and strength.

 

Breaking carabiners test preparation:

With my initial set of background questions answered (see Part 1 of this Carabiner study), I began to formulate my test method as I machined my carabiner testing fixtures. While I was working on my fixtures I also began accumulating old carabiners of all shapes and sizes. I contacted local Search & Rescue groups, climbing gyms, dirtbag friends, and even went as far as taking the oldest and most beat up 'biners from my own rack—which at the time was rather pathetic amalgamation of new and used gear.

The carabiners I was most interested in collecting were those that were extremely rope-worn. Having had climbed for a number of years up to that point, I found that some of my oldest and most heavily used pieces were suffering from wear where the rope abraded constantly in the same place.

<image1.JPG>

The state of my belay carabiner was especially shocking! Such an integral piece of gear as a belay biner should (ideally) be in perfect condition; the excess wear got me wondering if the loss of metal could compromise the strength of the piece. Not to mention the sometime sharp edge that can be produced as a result of extreme rope wear.

So, I sat down at the Instron machine with my box of old carabiners and I began to design my test.

The two main questions I wanted answers to:

Does a carabiner really break at the load (kN) printed on the spine?

 

How significantly (if at all) does moderate rope-wear effect the breaking strength of a carabiner?

 

Machine setup

To answer these questions, testing was conducted using the Cal Poly Mechanical Engineering Department’s Instron model 1331 that has a 100 kN (11 tons) capacity—which is like, Adam Ondrastrong!

The procedure used for breaking a carabiner basically involved loading the carabiner into the fixtures I made, clamping the fixtures into the machine, dialing a few settings, pressing record on a chart (which measured applied strength of the machine on the carabiner versus elongation of the carabiner as it stretched under the given load), and pressing ‘start’ to watch the breakage!

http://youtu.be/x_fTavmDwLw

Results

Non-locking carabiners tested:

Testing began on an assortment of non-locking carabiners all with either wire or solid gates (bent, straight, or key). The first carabiner tested was a new Black Diamond Posiwire. The Posiwire is D-shaped, has a key gate, and has closed gate rating of 25 kN and an open gate rating of 8 kN.

The results from the Single Pull To Failure test (that is the official term for pulling on a 'biner until it explodes) can be seen in the figure below.

<image2.JPG>

Half Dome, is that you?! Load vs. displacement curve for a new Black Diamond key gate carabiner initially closed and put through a Single Pull To Failure test. Highest peak represents failure of gate at 27.9kN; second, small peak on the right represents spine failure at 7.4kN after broken gate.

The linearity of the curve from 0 to 23 kN approximately represents the elastic deformation region of the closed carabiner. Above this range lies the plastic deformation region (where metal has stopped bending and is actually stretching like silly putty).

Failure first occurred at 27.9 kN when the gate exploded, and the spine of the carabiner failed at 7.4 kN. These results show an 11% increase from the printed closed gate rating on the carabiner and an 8% reduction in strength from the open gate rating. This trend was common for all tests done of this type, and shall be explained in detail later in the conclusion section.

Conclusions for non-locking carabiners

When testing non-locking carabiners, two things were generally observed to be constant from every test based on gate type:

- For non-locking wire gate carabiners, failure would typically occur the base of the spine with no initial failure at the gate.

- For non-locking key gate carabiners, the carabiner would fail at the end of the gate due to bending of the key hole.

Granted the rate of pull of the machine, testing was conducted slowly such that the loads could be considered static. This applied static load would first break the gate (for new carabiners, failure always occurred at a load greater than the closed gate rating), and the load would increase until the carabiner would fail at the spine around the open gate rating of the carabiner.

Almost always, the open gate rating would be greater than the applied load to open gate failure. It is important to take note of this discrepancy as it appeared frequently. This is most likely due to the fact that as the carabiner begins to deform before initial failure, it deforms past the point of elastic deformation and begins to permanently deform shortly before failing at the gate. When the gate fails, the plastic deformation serves to weaken the spine such that it breaks at a lesser value than the open gate rating specifies.

Given this hypothesis, it cannot be considered valid to extract two results from one SPTF test in order to compare both the open gate rating and the closed gate rating. Thus, for every test conducted, only the ultimate strength of the closed-gate test could be considered valid.

As an aside to testing the reduction in strength of a carabiner due to rope wear, one particularly interesting test was conducted on a severely corroded bent gate carabiner found on a canyoneering trip in Death Valley. The carabiner was found half buried in dirt and at the time of discovery would not open. With a little cleaning and some oil, it eventually opened and was subsequently used for clipping gear to a backpack before being donated for testing. No amount of cleaning could hide the thick layer of aluminum oxide penetrating the surface of the spine. This Omegalite 3 ‘biner had a closed gate rating of 25 kN and failed at merely 16 kN (still approximately 3,600 lbs)!

Locking carabiners tested:

For locking carabiners, testing was conducted on both new carabiners and old rope-worn carabiners. The hypothesis was that rope worn carabiners would have a significant reduction in strength over their new counterparts, due to the fact that the reduced cross sectional area of the rope worn area would significantly reduce the strength of the carabiner by creating stress concentration in that area. This is the same principle that explains the ease of breaking a wishbone.

Available for the test were two auto-locking belay carabiners, both with approximately 3 mm deep grooves from regular use belaying (see Figure 8). These two carabiners had a closed gate rating of 24 kN and an open gate rating of 8 kN. Both rope worn carabiners responded similarly to the SPTF test and failed within 0.5 kN of each other. The results of the test in graphical form are as follows.

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