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Flight shooting strings
avcase:
There is a standard test method for breaking strength, and it only tests the breaking strength of one strand. The measurement obtained is called the Breaking Tenacity, and it takes into account the linear density of the string to allow direct comparison regardless of differences in the thickness of the string.
www admet.com/how-to-perform-an-astm-d2256-thread-and-yarn-tensile-strength-test/
Alan
Badger:
I wonder how much difference using this method actually makes. I find even when I use a knot tied around two dowels it never breaks at the knot. Always in the middle of the string. I use a scale that records the highest reading and use a slow steady pull, it does seem consistent enough for being low tech. I always take several sample reading from each spool I buy.
avcase:
Steve,
My samples always broke at a knot. So I use a method similar to the one used by the textile industry. The only difference is that I use a longer length sample.
My digital scale didn't seem to handle the sudden breaking of the string and would sometimes give inconsistent results. So I still use the method of suspending a bucket from one end of the string and slowly filling it with water until it breaks. Then I weigh the bucket of water afterwards. Maybe I should invest in a better scale. It would sure be a lot more convenient to do it your way.
Do you also weigh the thread to get an idea of mass per unit length? If you divide the breaking strength by the mass per unit length, then it allows you to directly compare different sizes.
Alan
Badger:
--- Quote from: avcase on October 20, 2016, 10:06:47 pm ---Steve,
My samples always broke at a knot. So I use a method similar to the one used by the textile industry. The only difference is that I use a longer length sample.
My digital scale didn't seem to handle the sudden breaking of the string and would sometimes give inconsistent results. So I still use the method of suspending a bucket from one end of the string and slowly filling it with water until it breaks. Then I weigh the bucket of water afterwards. Maybe I should invest in a better scale. It would sure be a lot more convenient to do it your way.
Do you also weigh the thread to get an idea of mass per unit length? If you divide the breaking strength by the mass per unit length, then it allows you to directly compare
different sizes.
Alan
I always make that comparison. The only thing I have never been sure of is the effect of having more or less strands.
--- End quote ---
avcase:
I recently received some of the Swedish Bockens unbleached linen thread and ran into a perplexing issue that makes me question how I've tested and ranked all my linen so far.
Without much thought, I ran the sample from my house, to my work shop to do a series of break tests, where I noticed a very interesting trend. Due to random interruptions, it took me about an hour and a half to complete five breaking strength tests. The first test broke at 9.8#, and each successive test yielded a slightly higher breaking strength than the one before. The last test broke at 12.2#. I wondered what was going on here? I used a very consistent method, where the sample supports a large bucket that was slowly filled with water until the string snapped. The bucket of water was then weighed on a recently calibrated and certified scale to obtain the breaking strength of the sample. I threw out any results where the test sample may have broken at one of the supports.
I then decided to re-test my best performing 35/3 Barbours material and was shocked when it performed less than 60% as strong as the last time I tested it! The thread felt very brittle and I could break it by hand without too much effort. Something seemed very wrong. I sat this information aside, not sure what to make of it.
A couple days later, I was back in the workshop and tried breaking the Barbour's sample again by hand, but this time it felt completely different. It wasn't going to let go without cutting my fingers! How can this be? It was then I realized that the last time I used this Barbour's thread was in an air conditioned room in extremely dry conditions at the Bonneville Salt Flats, and I had sealed it in a plastic bag before returning home in Oregon. This may have kept the thread in a very dry condition, leaving it very brittle.
It is well known that linen loses significant strength as it becomes very dry. The humidity next to the air conditioner unit at Bonneville may have been just a few percent when I sealed the Barbour's thread in the plastic bag. Something similar may have been happening when I was testing the unbleached Bockens thread. Prior to my break tests, the Bockens thread was stored in the house near a de-humidifier. I then moved it to my workshop (without climate control) to conduct the tests, which was near 100% humidity level during our cool misty-rainy weather. My theory is that the increasing break strengths that I measured were due to the thread gradually becoming acclimated to the higher humidity environment in my workshop!
So this throws all the data I have collected on various linen samples in doubt. They were all tested in different conditions at different times of the year. How do I compare one against another in a meaningful way?
Alan
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