Climbing Science: A Study on Carabiner Testing & Strength, Part 3

carabiner strength test

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


Testing the strength of textile gear

Testing for textile gear began after carabiner testing. Having seen the seemingly negligible effect of rope wear on the strength of a carabiner and the great effect of corrosion on the strength reduction of a carabiner, I drafted a hypothesis in which the effect of age and wear on textile gear would be much more prevalent than was seen with aluminum gear.  

Given the small amount of used gear available for testing, results were limited with varying accuracy to the tests conducted on quickdraw dogbones and one test on a Blue Water sling. Quickdraw dogbones were most plentifully available for testing, old and new.

testing results
Load vs. displacement curve for a Blue Water sling (rating unknown). The sling being old and brittle broke at 13.7 kN—well below the CE standard for 22kN minimum for a typical climbing sling. Unlike the ‘Halfdome’ shape from a breaking carabiner, here you can see that slings stretch continuously until they fail all at once.

For all quickdraw dogbones tested, the results showed generally the same curve for applied load vs. displacement, and therefore will not be printed in this report. The loads at which each dogbone failed can be found in the results section.  

To summarize the trend between rated load and applied load to failure in terms of age of the dogbone, the older the dogbone, the greater the discrepancy. Generally, the older the dogbone, the lower the applied load, which caused failure. In the case of the Mammut and Mad Rock dogbones, a difference of 10 years of age showed almost a 30% percent reduction in strength … That’s a lot!

Figure 4. Mammut vs. Mad Rock dogbone comparison

1 year old tested dogbone
1 year-old Mad Rock dogbone, 22 kN rating, post testing.
10 year old tested dogbone
10 year-old Mammut dogbone, 25 kN rating, post testing.

Testing was initially planned to cover the strength of old webbing compared to the strength of new webbing, however, all of the old webbing acquired had no specifications with it and was therefore impossible to identify, research, and compare to anything new. Please see Table 2 for a tabulated list of results for every piece of gear tested.

Table 2. Comparison of all ratings to tested failure loads:

Gear Donated/Bought Printed Closed Gate Rating, kN (carabiners) Printed Strength, kN (slings and dogbones) Tested Strength, kN Percent Difference
1 rope worn bent-gate carabiner 19 17.8 -6.3%
2 rope worn Black Diamond auto locking belay ‘biners 24 28.8 20.0%
2 Black Diamond oval shaped non-locking carabiners 20 21.1 5.5%
1 Black Diamond Posiwire non-locking key-gate 25 26.5 6.0%
1 Extremely corroded Omegalite 3 bent gate carabiner 25 16.2 -35.2%
1 D-shaped, I-beam x-section, wire-gate ‘biner 24 27.8 15.8%
1 New Madrock quickdraw dogbone 22 24.1 9.5%
2 new Black Diamond quickdraw dogbones 22 23.7 7.7%
2 Mammut dogbones, aged 10 years, stale, faded 25 18.3 -26.8%

 

Conclusion from textile gear testing

Given the results tabulated in Table 2, textile gear generally sees a significant reduction in strength over rope worn (or even just old) aluminum carabiners. A direct comparison cannot necessarily be made granted the fact that dogbones and carabiners wear differently, but given that both would be used with the same frequency by a climber over the span of, say, a ten year period—the information gained from this testing gives a climber a sense of what gear they ought to retire first.  

It should be noted that the 10 year-old Mammut dogbones used in this test had no signs of significant wear, other than being slightly brittle. To a beginner climber with a low budget and little experience with quickdraws, these dogbones may have seemed perfectly fine to purchase off a second hand vendor, but clearly would not have been safe to take a serious fall on!

 

Related: Understanding Gear: Carabiners, Quickdraws

 

Conclusions from overall study

Old aluminum gear can generally be trusted more than old textile gear. According to the results of testing the two aluminum rope worn belay carabiners (rope wear approximately 2 mm deep), no significant reduction in strength was seen at all. Actually, even with significant rope wear, these belay carabiners still failed 4.8 kN higher than their closed gate rating.  

This trend observed in carabiners of breaking at a greater applied load than their closed gate rating predicted was true of every carabiner tested, aside from the extremely corroded bent-gate carabiner found in Death Valley and the one extremely rope worn bent gate carabiner. This trend is attributed to the fact that the closed gate rating is a minimum allowable load, not ultimate.  

Reviewing the load vs. displacement curve for a new Black Diamond key gate carabiner, we see that the ultimate strength of the carabiner was 27.8 kN, where its closed gate rating was merely 24 kN. Given the load vs. displacement curve, it is observed that the slope of the curve changes at about 24 kN. In comparison to the stress strain curve of a ductile metal [8], the slope ought to change when the yield strength of the material is passed. Given the slope change of Figure 5 at the 24 kN, research suggests that the printed carabiner ratings correlate the carabiner’s yield strength—not ultimate strength.  

 

References

[1] Bassler, Jimmy. “Black Diamond HQ Tour.” Personal interview. 30 Mar. 2012.
[2] BSI. “Online source for Standards.” Personal Protective Equipment Against Falls from a Height.   BSI. 2 Apr. 2012.
< http://shop.bsigroup.com/ProductDetail/?pid=000000000030123018>.
[3] Blair, K (2001). Carabiner Testing: Fatigue Presentation. Retrieved 10 Apr. 2012 from MIT website: web.mit.edu/sp255/www/reference_vault/Fatigue_Presentation.pdf
[4] Breaking a Carabiner at the Black Diamond Factory – YouTube. Perf. Jimmy Basler. YouTube. 22 Mar. 2008. Web. 12 May. 2009. <http://www.youtube.com/watch?v=x_fTavmDwLw&feature=results_video&playnext=1&list=PL1B35A898B5F1D0C6>.
[5] UIAA Mountain Equipment Testing – YouTube. YouTube. Accessed 22 Mar. 2008. Posted Web. 25 Oct. 2007.
<http://www.youtube.com/watch?v=H3Cg8homvoU>.
[6] Instron. 1330 Series Servohydraulic Fatigue Testing Machines.
<http://www.instron.us/wa/product/Instron-1330-Series-Servohydraulic-Fatigue-Testing-Machines.aspx>
[7] Carabiner Fail Test – YouTube. Perf. BYU Idaho. YouTube. 8 Mar. 2012. Web. 11 Dec. 2011. < http://www.youtube.com/watch?v=13poPfa8Zso>.
[8] Ashby, M. Shercliff, H. Cebon, D. (2008). Materials engineering, science, processing, and design.  (1 ed., reprinted 2008). Elsevier Ltd.

Now to you

How frequently do you replace your dogbones and slings? Have you ever noticed significant wear on your gear? Let us know your experience in the comments below!

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