Bizarre (but Informative) Break Test

This is for all those people out there that can't believe a splice can hold together. The idea for this test came to me about a year ago, but I wasn't able to break anything at that time so the idea went nowhere.

Yesterday I was chopping off chunks of some 3/8 in. Tenex Tec for experiments I was doing when I came to a defective section of rope. Rather than waste it, I realized this was my chance to do my little experiment. The rope was new, by the way, and the defect consisted of a broken yarn and another yarn that had been partially pulled out of the rope. Because the reddish dye was consistent throughout, it seems likely this happened at the factory!

I constructed a test piece from this section about 4.5 feet long. At each end I made a normal spliced eye with a tapered bury. The defect was located at the midway point between the eyes. Then I cut another piece of the 3/8 in. rope about 20 inches long and tapered both ends. This short piece I then inserted into the damaged rope so it was completely buried and centered. The center of the buried slug, in other words, was located right at the defect.

Next I very lightly wrapped some vinyl tape an inch or so on either side of the defect to keep any cover strands from unravelling as I worked. Finally I carefully worsened the defect by completely severing cover strands until half the clockwise strands and half the counter-clockwise strands were gone.

Note that no stitching was applied, and the vinyl tape was about as loose as I could make it.

I installed the rope in my break-test rig and started pulling. The first picture shows the center section at 1000 lbs. tension. (The other, smaller rope seen in the photo is part of my recoil snubbing system.)

I continued applying tension until a loud BANG! announced the rope had snapped. The last photo shows the result. The weird repair in the center was still intact, and the rope broke, as always, at the end of one of the buries.

Interesting. Please keep sharing your experiments with us, they are educational. I'm curious how you put together your rope breaking machine.

Yes, do go on. Most interesting.

Impressive... What was the final load at breaking point?

Say on the subject a thought occured to me .

Some 30 plus years ago the coast guard did the most comprehensive study on rope stresses ever done up to that time . My ex wife was a research assistant during that test which took place over a period of a year using all known ropes and lines in use at that time .

I can't seem to find any record of it on the net though but I'm sure it's out there some place .

CurSedVoyce said:

Impressive... What was the final load at breaking point?

Click to expand...

The weird repair broke at 4754 lbs. Another length of the same rope with two regulation tapered splices broke at 5554 lbs. I think this shows the buried repair slug wasn't quite long enough fully and equally transfer the load to the undamaged section of rope. Had I put some stitching where the tapes were, or had the slug been 3 or 4 inches longer, I'm sure the break strength would have been right up there at 5500 lbs.

My testing rig consists of a fallen tree to anchor to, two lengths of heavy chain to make adjustable anchors, a hydraulic cylinder with a 24 inch stroke, a load cell with 10,000-lb. capacity, a digital readout that holds the peak reading, and a hand-operated hydraulic pump. Each pump stroke advances the piston about 1/6 inch.