Material tests on rope, cord, webbing and even tensile tests on metal are done in tension machines that apply a relatively low rate of strain (displacement) until the breaking point is reached. It is often the case that materials will exhibit different ultimate strengths (often higher strengths) when the load is applied very suddenly. Jim McLane
> Date: Fri, 4 Feb 2011 14:07:12 -0500 > To: [email protected] > From: [email protected] > Subject: [Texascavers] Re: fall factor > > Seems like I heard somewhere that dead pig carcasses were > used for just this sort of test somewhere, but the details elude > me. That should give a pretty realistic assessment of the dynamics > of the system, if you could get a pig into an appropriate harness. > > Mark > > At 01:12 PM 2/4/2011, Mixon Bill wrote: > >The concept of fall factor in assessing the load on belays can be > >overdone. Yes, it is probably meaningful when one is talking about a > >fall of 40 feet on 20 feet of rope (which would be fall factor 2, if I > >understand it). But there is a problem when discussing very short > >falls, like 2 feet on a 1-foot cowstail. No matter how static the > >cowstail might be, there is enough give in your harness and your body > >to prevent the sudden stop that is the basis of worrying about fall > >factors. I'd like to see a figure for the peak stress put on a short > >length of static rope (it could even be a steel cable for the > >experiment) by a caver falling 2 or 3 feet in his harness--not a > >theoretical figure, but rather a dynomometer reading. (But even that > >would hurt....) It would be a lot different from that of a concrete > >block of the same weight attacted rigidly to the cable. Basically, if > >you fall 1 or 2 times the length of your cowstail, your harness and > >your butt are the dynamic protection. > > > >For a long drop, like a fall of a lead climber from above his last > >belay point, the slop available in harness stretch and body > >compression is a lot smaller fraction of the fall distance and > >provides less protection. In such a case, the stretch of the rope is > >critical to avoid death. -- Mixon > > Please reply to [email protected] > Permanent email address is [email protected] > > > --------------------------------------------------------------------- > Visit our website: http://texascavers.com > To unsubscribe, e-mail: [email protected] > For additional commands, e-mail: [email protected] >
