Calculating load handling of stretch fabrics

[Blargendarg]

While I am still immersed endlessly iterating on a 'curved end' hammock build, a recent conversation gave me some ideas about incorporating some amount of robust stretchy fabric(ie thick spandex or neoprene) in a future design.

I can find plenty of info about calculating the stretch *percentage* of different fabrics, but given that these are mostly for clothing applications, nothing about calculating the minimal load that would cause the fabric to reach 100%, er, stretchativity. Given that in a hammock application, load handling would be dynamic and the max amount would directly correlate to the square yardage of elastic fabric involved, it would be nice to be able to find a capacity or a range - rather than buying a bunch of fabric and testing it.

For example, if you could determine the amount of static load that would cause a square yard of a particular type of spandex to stretch to say 50% capacity, that would probably be able to handle m/any load spikes.

God only knows if I'm using any of the terms correctly- my fiber design experience is pretty limited and although I've dug into tensile fabric design a bit, it's awfully complex field and as far as I can tell the textbooks are all either out of print or hundreds of dollars. I haven't found anything searching here or on the web, but maybe I don't have the right terms? I'd love it if someone could point me in the right direction. Thanksdood(s).

[SilvrSurfr]

A neoprene hammock? That's not gonna breathe very well, and I doubt "thick" spandex will be much better. Neither one would be sufficiently lightweight for backpacking.

[Blargendarg]

Nah, not the whole hammock, just certain sections, which introduces problems of its own, but I'd be willing to spend some time chasing it down to see if I can get a little bit of dynamic adjustment while leaving other sections more supportive. I'm just looking to find out if there's info on static loading of the fabric, say 2 way to avoid further complications, or even whether if I'm thinking about the material in the right way. There tends to be a lack of info when it comes to specs from manufacturers in general that some vendors do a great job of filling in.

So I don't know if this info is even available, but considering the amount of time it'll take to test the fabrics and collect the data, I figured I'd ask if anyone had knowledge or experience with loading these stretchy fabrics... or hey, even suggestions on how to approach testing them, because I'll certainly do that if I have to.

[SilvrSurfr]

All I can say is that neoprene and "thick" spandex hammocks haven't ever been considered by anyone, to my knowledge, so you're on your own. Good luck!

[SilvrSurfr]

Nah, not the whole hammock, just certain sections, which introduces problems of its own, but I'd be willing to spend some time chasing it down to see if I can get a little bit of dynamic adjustment while leaving other sections more supportive.

A sectional hammock? Like an ENO? Those seams running down the length of the hammock are irritating. And the additional points of failure created by all those seams on those sections? Priceless.

[Blargendarg]

Nope, not like that. Though there are plenty of tensile fabric applications that incorporate seams and handle far more load than a hammock ever will. It all depends on the methods and materials involved.

There is really not so much difference in the fabrics that *are* commonly used for hammocks. From initial loading to failure is a certain range. And with at least one vendor the max load listed is not to failure but to a point where the fabric is so close to failure that it's no longer useful anyway. I'm simply looking to find midrange specs for fabrics that, used in small amounts, I think might make support a little bit more dynamic.

[WV]

Nah, not the whole hammock, just certain sections, which introduces problems of its own, but I'd be willing to spend some time chasing it down to see if I can get a little bit of dynamic adjustment while leaving other sections more supportive.

When I started making adjustable hammocks by cutting off the sections of fabric that weren't directly under me and replacing them with clews, I found that making some of the clews out of bungee instead of dyneema fishing line gave variable stretch, as well as adjustability. It also saved weight, rather than adding extra.

I'm just looking to find out if there's info on static loading of the fabric, say 2 way to avoid further complications, or even whether if I'm thinking about the material in the right way. There tends to be a lack of info when it comes to specs from manufacturers in general that some vendors do a great job of filling in.

So I don't know if this info is even available, but considering the amount of time it'll take to test the fabrics and collect the data, I figured I'd ask if anyone had knowledge or experience with loading these stretchy fabrics... or hey, even suggestions on how to approach testing them, because I'll certainly do that if I have to.

You could try to find out if anyone has used stretchy fabric in lawn chairs, but you're probably better off doing your own pull tests. You can compare weight and breathability at the same time. By the way, did you try using advanced search in HF for "spandex". Someone (maybe leiavoia) has mentioned it.

[slugbait]

I envision the day when hammock fabrics may be custom woven with different areas of stretch and non-stretch; perhaps computer mapped for each individual.

[Blargendarg]

I found that making some of the clews out of bungee instead of dyneema fishing line gave variable stretch, as well as adjustability

Yep, that makes sense. I haven't used stretch materials, but my past experiments with clew ends were kind of fussy and so I hoped to use a fabric instead so long as a small enough(light enough) section could handle the weight.

Someone (maybe leiavoia) has mentioned it.

Have they ever! I'm sure I missed this because I've been going round and round, search alternately for spandex, Lycra and elastane. Sometimes this uncovers things I didn't expect.

I was able to find a couple of scholarly papers last night that were interesting. At least I learne a few new search terms and that I shouldn't be looking to hit 50% of failure load but much, much less. Even 35% of the failure load on spandex reduces its ability to return to shape to something like 12% and extends the length to boot.

Anyway I guess I ought to head to JoAnn and see what I can find to test. Leiavoia's great article didn't include much that can transfer over, but the tip on looking for 10% spandex and up to find utility fabrics is a good one. Interestingly, in another paper it was pointed that as the spandex content increases, the max load decreases, which I guess makes sense. It provides the elasticity, but the fabric it's combined with is what provides the vast amount of the strength. I need to go back and work out all the terms, but there was a tested 70 denier elastane fabric that provided support at the rate of .O6lb/insq which at least seems doable. It wouldn't win any ultralight honors I expect, but ought to do a lot to respond to the differences in loading when the user changes position.

[Blargendarg]

I envision the day when hammock fabrics may be custom woven with different areas of stretch and non-stretch; perhaps computer mapped for each individual.

It could probably do a lot to provide a custom fit, especially if you tend to sleep one way, although the reason I find hammock design so interesting is that the support has to respond as people change position. Although in theory, the computer could at least partly account for this by weaving more elastic fibers into certain sections.

So in the scifi future you will get into a kind of giant Brannock device and spend the night in its hammock which of course senses every movement and delivers complementary orange juice.

And then it weaves the hammock. Hey, so much of the stuff from the old Star Treks came true.