Calculating load handling of stretch fabrics

[leiavoia]

I don't have any numerical answers, but a few direct observations that can at least bound the problem:

I have a yard of regular spandex that i roped over a pull-up bar and hung off. It supports my entire bodyweight BUT the stretch maxes out long before completely loaded. Based on some exercise stretch bands i have, i would estimate that my spandex "rope" made from 36" width regular spandex maxes out the stretch at ~80lbs of force. For a hammock, thats probably not going to be enough, even if you doubled it up.

Notes:

Regular spandex is going to be much stronger than "stretch mesh" and other derivatives. Its also going to be much heavier. Its surprisingly sturdy stuff.

Regular non-stretch fabrics used for hammock bodies have a certain amount of inherent stretch anyway. Stretchier fabrics are not everyone's cup of tea though. Some people like the harder fabrics for support.

Stretchy hammock fabrics tend to leave you feeling... sunk down, for lack of a better term. Your heavier areas will sink in very far and your lighter areas will stay up high, giving you an awkward "caught in a net" position. My krinkle-taffeta tablecloth hammock is like this.

If you tried to incorporate stretch fabrics into a segment of a hammock body, you run into the problem of stitching. If you evenly load a line of stitches, its not a concern (many hammocks have a stitched end channel). But if your bodyweight in the hammock is mostly down the middle and you load mostly a few stitches in the middle, that could be a point of failure.

Positioning a stretchy hammock is also tricky. If you set it up to be 12" off the ground, you expect it to stay that way when you get in. If instead you sink into the ground, thats bad.

You might also look into Mayan style hammocks. They are typically made with cotton yarns but they exhibit certain stretchy dynamics you might like.

[SilvrSurfr]

Stretchy hammock fabrics tend to leave you feeling... sunk down, for lack of a better term. Your heavier areas will sink in very far and your lighter areas will stay up high, giving you an awkward "caught in a net" position. My krinkle-taffeta tablecloth hammock is like this.

My krinkle-taffeta tablecloth hammocks are polyester, which have minimal stretch anywhere. I'm surprised you have such issues with a polyester hammock.

[Blargendarg]

I don't have any numerical answers, but a few direct observations that can at least bound the problem:

I have a yard of regular spandex that i roped over a pull-up bar and hung off. It supports my entire bodyweight BUT the stretch maxes out long before completely loaded. Based on some exercise stretch bands i have, i would estimate that my spandex "rope" made from 36" width regular spandex maxes out the stretch at ~80lbs of force. For a hammock, thats probably not going to be enough, even if you doubled it up.

Thanks for the info- yeah, it may be that there isn't any fabric that has the specs I'm looking for. I'm not terribly worried about weight as I was thinking of using small amounts of it. This is further complicated by the fact that my intended use wouldn't use spandex (or whatever elastic fabric that can return to form after stretching) to handle the entire bodyweight. I tend to think of gathered end hammock support in terms of a series of 'support axes' along the length of the hammock. It's an oversimplification, but it works well enough to help in the design process. Some of these support axes would be entirely a supportive poly fabric - I like Hexon an awful lot - no spandex and no seams, so how load would be distributed is a complex kind of thing that's probably best explored by protoyping, at least at first.

I just wanted to get a better idea about the range of these kind of fabrics and any data I could find about how much I might expect as a starting point. There are some very supportive fabrics out there like what's used in otc knee and ankle braces, but I've found it difficult to find any useful specs. Explaining the design is kind of hard to do, especially because it's not even fully formed, but I do appreciate the perspectives I've gotten on it and I felt like I ought to include *something* about how I intend to use it. It may be that approaching dynamic support would be better via WV's clew end idea.... there's one way to find out.