DMM is regularly approached by university researchers and businesses looking to use our research and testing facilities. Together with our engineering expertise this makes us an ideal partner in a commercial partnership working on product development.
Dan Commander, undertaking his final year project for his BSc degree in Outdoor Ed. with Physical Education, at Liverpool John Moores University, was the latest researcher to arrange to use our test facilities at the DMM factory in Llanberis.
Dan's project is based around making a comparison of the structural integrity of in-situ, mislaid and retired climbing hardware, in relation to its visual wear and damage i.e. is it possible to take a piece of gear with an unknown history and accurately estimate whether it was safe to use based on it’s physical appearance?
Dan had a wide range of carabiners, wires and slings; much of which was abandoned kit that had been recovered from the crags of Wales over the last three years.
Tests were carried out on the gear using one of our tensile strength rigs, performing single pull to failure tests according to the relevant CEN test procedure.
There were several DMM carabiners amongst the items being tested and owing to the batch code stamped on them as part of our quality control system, we were able to date these products.
From a DMM perspective the results were reassuring:
- A Lynx bent-gate snaplink carabiner from November 1993, retired from use by the Liverpool University climbing club, failed at 26.48 kN although rated at 24 kN.
- A 2006 Tru Clip screw-gate recovered from the Hyll Drem Girdle with a 26 kN rating broke at 31.25 kN.
- A 2007 Prowire found on the ground at Haytor showed a similar story, failing above its 24 kN rating at 26.67 kN.
Two contributory factors to this are that at DMM we aim to build in a substantial safety margin above the stated rating and that it isn't unusual for the alloys used - in the absence of corrosion - for them to become stronger, although less ductile, with age. Even an ancient, rusty, pre-1990 DMM Locknut 9 on wire that was recovered from Great Gully on Craig yr Ysfa, and which was originally rated at 12kN, reached 13.54kN before it snapped.
However the textile products tested showed they were a lot more susceptible to damage with age. Two found DMM Dynatec quickdraws (11 mm x 12 cm) showing little cosmetic damage and made in 2008, broke at 20 kN rather than the stated 22 kN or above. Whilst two slings from another manufacturer that had begun life on the university climbing rack in 2000 but which were now retired from use, failed around the 17.5 kN mark. This is a trend that is supported by internal tests that have seen strength losses of up to 60% on slings that appear only slightly abraded.
Dan commented: "I haven't had the chance to analyse all the gear yet but a couple of quick conclusions already come to mind."
"Firstly, out of the 21 wires tested, 12 broke at the top bend and six at the bottom bend. This I believe is due to the concentration of the forces at the bends in the wire. It would therefore make sense that these areas of the wire are the most critical for damage, so that any damage in those areas is likely to have a particularly detrimental effect on the wires structural integrity."
"Secondly, taking the 16 of the 56 test items that scored above three on the equipment damage scale, with five the worst, and considering the most visually damaged area on an item as its estimated failure point, only seven actually failed at these stated points. This would suggest that damage is place specific."
Historically, manufacturers have recommended as a rough rule of thumb, five years for the use of soft goods such as slings and ten years for hardware such as carabiners. Clearly though, this depends hugely on the frequency use, where it's been used and the severity of use.