Author Topic: Ring bend failure mode (#1412)  (Read 3286 times)

agent_smith

  • Sr. Member
  • *****
  • Posts: 1377
Ring bend failure mode (#1412)
« on: November 18, 2018, 03:17:45 PM »
Accident report and investigation

Knot: #296 / #1412  (Ring bend / water knot / tape knot)
Date: July 23, 2016

Download link: https://www.nps.gov/aboutus/foia/upload/GRTE_GaryFalk_Fatality_Incident-Report_NP16114877.pdf
NOTE: The pdf file is too large to upload.

Brief summary:
It is hypothesized that #1412 - when tied in webbing (ie tape) - can work loose under cyclic loading conditions.
This failure mode is exacerbated if using webbing that has a 'slick' texture - particularly dyneema/spectra type material.
Furthermore, it is thought that this failure mode is more likely at lower loads.
« Last Edit: November 19, 2018, 05:16:55 AM by agent_smith »

SS369

  • Global Moderator
  • Sr. Member
  • *****
  • Posts: 1964
Re: Ring bend failure mode (#1412)
« Reply #1 on: November 18, 2018, 07:43:23 PM »
Thank you Mark, lots and lots of info there.
I hadn't been aware of how much incident reports contained and it is an eye opener.

I noticed in the photos that the recovered webbing sling's remaining overhand is so very close to the end. And it looks like the coiled, on harness picture, shows that seemed to be its normal place although loose.
Perhaps the installation and usage angles of the sling also contributed to the loosening/failure. The wider the angle, the more strain on the join. Four feet is not a lot of sling most times. I generally carry multiple 25 ft.x 1 inch nylon webbing because I'd rather double, triple, etc. then run shy. And yes my pack out is heavy.  ;)

Short tails, cyclic loading and wide angles equals chancy business.

Perhaps it was a case of experienced complacency. ?

S

Harold Kahl

  • Full Member
  • ***
  • Posts: 73
Re: Ring bend failure mode (#1412)
« Reply #2 on: November 19, 2018, 02:50:57 AM »
It's good to know about these incidents, to remind us how dangerous it is to become complacent.

Isn't that photo a Euro Death Knot rather than a water knot?