For failure modes: These appear to have "broken", "burst", "torn", or "sheared", definitely not "separated."
An experienced tech or engineer might be able to read that a tear originated from some identifiable worn or broken points. That is very often true for broken metal parts. I hope one of them will volunteer here to inspect these. So, don't throw away the broken sections.
Number of uses of straps loaded well below the breaking strenght should be in the hundreds-- as in 'days of several years". If it were otherwise, lots of strapped-down cargo would be reported flying from trucks every day into the paths of other trucks and passenger vehicles.
You may very well have repeatedly broken or weakened fibers on the corners of 4x4 post, softening up the strap for an eventual bursting failure. Best way to reduce stress from that source in the future would be by radiusing the corners of the posts, or pre-wrapping the post with a padding layer.
But, there's a lot of crap out there in the market, like plastic cable ties weaker than the lightest fishing lines.
i bet your culprit is the use of straps on 4X4 posts. I tried to hang some at my sister in laws. They have a new house with a new fence. The posts edges were sharp and I saw some fraying in just a few minutes of hanging. I ended up taking it down and and trying to figure out what do at my house to protect the straps. I am thinking garden piece to protect the strap.
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I know this isn't the best thing to do but I leave my tree straps up in my yard all the time (no damage to the tree in over two year). I can just hook my whoops up and I'm in relax mode. They have been exposed to UV, heat, freezing temps, rain, snow and my fat ars. NO problems yet but now you got me a little nervous. I'm more worried about the stitching I did for the loops than the webbing.
The Ebay Seller I got my polypro webbing from has this in their descriptions:
"Some rolls may contain factory splices. If you need a continuous roll let us know"
Splices are typically stronger than regular rope/strap/cable, but only if done correctly.
Maybe you got a factory splice with the machne operator hung-over on a Monday AM?
If in doubt, go with this next time :
2100 lbs tensile strength
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Glad you are OK.
I'm new to this and should "hang" for the first time in the next month.
Before ordering my tree straps I was confused about Polypropylene vs Polyester. I read somewhere that Polypropylene is more susceptible to abrasion damage than polyester, so I went with polyester.
I read the thread of few times and didn't see you specify which poly these straps were.