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Dan Johnson
(Seattle)

Locale: PNW
Polycryo Strength Analysis on 02/12/2012 17:39:35 MST Print View

So after making my tarp out of this stuff I figure I better do some testing on it since not very many people have tried to use it as a tarp. Maybe they're smarter then me :)

The things I wanted to find out were mainly were:

1) What is the best type of tie-out?
2) How much Tape is needed on the tie-outs?
3) What is the tensil strength of this material?
4) How does this material act in stress loading?
5) How strong is the double sided tape provided in the box?

Please note that I am not a scientist but rather a very curious frugal person. Nothing I did is very scientific but it is better to have "some" data then no data at all. And of course I took lots of pictures!

All test smaples were about 3" wide and 20 something inches long. I first started out using a tie-out that I have on my tarp that I made. It's basically the tape folded over itself with a hole thru it. The tape used was Gorilla Glue Tape.

test

This tie-out ripped with pretty minimal effort. It still took a good pull but I thought it would have done better. This is what it looked like after.
test

I then tried a plastic washer sandwiched between the tape. This was an idea given to me by another member here and I'm sure happy I tired it out. Sure enough the plastic washer that measures 3/4" diameter worked like a charm. So well in fact that I used it exclusively on every test here after simply because it wouldn't rip out.
test

Next I needed to know how much tape to use on the tie-outs. This is very important to know since the tape is the heaviest part of the tarp. I first started out with a 4" piece of tape folded over with a contact length of 1" on the tarp body. This allowed the other inch to be used to sandwich the washer. You can see this on the photo above. I then did the same thing but used a 5" length piece of tape folded over. I kept the same washer distance but now I had a 1.5" contact length on the tarp. Then I strung up my super scientific measuring tool to see which side would pull off first.
test

Sure the test area looks a little "elementary" but hey, it worked. In the photo it looks like the bag is touching the ground but it is actually about 2" from it. What I found out next surprised me. I started loading up the weights. First 5lbs then 10lbs then 15lbs then 20lbs etc... it finally failed at 35 lbs. And it was the material itself that broke. Both tie-outs held beautifuly. The material upon failure made a loud snapping noise that was pretty loud. The polycryo had sheared directly in a straight line across the middle of the sample. It should be noted that on every sample conducted the polycryo sheared off in the very middle. Not near the tie-out, but in the very middle. I found this pretty interesting. Upon further review I can tell you that when loaded the polycryo does stretch. Each sample stretched about 6" before failure. It should also be noted that I measured the distance each sample of polycryo slipped from the tape. And interesting also was that there was not any slipping of the material from the tape on any test.

So after that test I could conclude that both tie-outs were overkill for the material. I then tried the test with a different tie-out. This one is a 1" piece of tape that is 4" long with the washer with a contact length of 1" on the polycryo.
test

The test on this tie-out was only about 20lbs. I'm not a scientist (remember), but I think that it failed sooner due the concentrated stress it applied to the very center of the sample. Versus the previous samples that were done with 2" wide tape and were able to distibute the force thru alomst the entire sample width of 3".

Here is a photo of what the polycryo looks like under 30lbs of force.
test
After the foroce had been applied I removed the load to examine the material. Sure enough it stretched a little but it didn't show too much signs of deformation.

Next I wanted to see how the material did when I applied a single line of it's double sided tape that is included in the packaging on the sample under stress. I figured if it improves the strength then it could be useful to help out critical areas.
test

The test sample held about 40lbs and just like all the other tests it failed in the very center. Here's an after photo of the stressed piece.
test

The next test was to figure out which is stronger: The polycryo or the doubled sided tape. I made the same 4" tie-outs on the sample and applied force till failure. I cut the sample in half and then rejoined them with the tape. I then applied force till failure. I found out that the double sided tape has a stronger hold then the material. The polycryo sheared in half on one of the sections and the taped connection looked just like new without any slipping of the material on the tape.
test


I hope this series of tests shines some light on polycryo for everyone. I know it did for me. I guess what I can conclude is this. My original tarp used WAY TOO MUCH tape and the tie-outs aren't nearly as strong as they could be if I used washers. For all further polycryo shelters or anything I make with the material I think I'll "hem" the edges with the double sided tape as it showed it is stronger then without it. Also, I'm sure someone could use another type of tape to reduce weight but Gorialla Glue Tape is what I had laying around and from everyone at Home Depot they said it was the strongest they sell.

Now, Lets discuss!

Nathan Lare
(cirque) - MLife
RE: Polycryo Strength Analysis on 02/12/2012 18:10:05 MST Print View

That is really good information. Do you plan to perform another test to simulate your setup (an entire section of the film with a tieout on each end...then suspend it over a line the simulate your setup and fixing one tieout and applying weight to the other tieout)? It would be interesting to know if it would fail at the ridgeline, or half way down one of the panels.

a b
(Ice-axe)
Polycro strength analysis on 02/12/2012 18:30:25 MST Print View

Really nice testing.
I was wondering something simliar to the above.
How would polycro hold up to being supported by a pole such as a pyramid.
I am thinking you would just reinforce the area where the pole contacts the polycro with the tape.
Or perhaps a tape pull out at the peak with a washer that fits over a trekking pole tip.
At any rate, this is really interesting stuff.
35 lbs of force is quite a lot of shear strength for such an inexpensive material.

John Donewar
(Newton) - MLife

Locale: Southeastern Louisiana
Re: Polycryo Strength Analysis on 02/12/2012 18:53:54 MST Print View

I'm curious as to what a piece of polycryo set up as say an A frame 6' x 8' with hemmed edges but an unreinforced ridge line would fare out. In particular I wonder what pressure the material would have to be under at the ridge line in order to achieve a tight pitch.

Since the material does stretch when under pressure getting a tight pitch may not be that difficult.

If memory serves, sunlight a.k.a. ultraviolet light will shrink this material to a point. I'm wondering how it will affect its strength and elasticity after being exposed to sunlight.

What kind of plastic washers are those? Are they available at Home Depot? Did you source your polycryo from Home Depot? When I ask for it by name at my local "Depot" all I get is blank stares. If I ask for the clear window insulating film the stares continue. Realize that I live in Southeast Louisiana and we're more familiar with trying to stay cool. ;-)

Party On,

Newton

Steven Evans
(Steve_Evans) - MLife

Locale: Canada
Re: Polycro strength analysis on 02/12/2012 19:03:04 MST Print View

I'm actually glad you're not a scientist :) You have done some nice work here.

35 lbs really is quite a bit. Didn't BPL just post an article saying something along the lines that a tieout should withstand 15-20 lbs. I could be totally wrong, but I thought I read that on here.

Anyway, of particular interest to me was how much it had to stretch before breaking. It seems that would work in its favour during sudden wind gusts. I also wonder how much you could stretch it and have it return to it's original size (ie. how far can it stretch before being permanently deformed)

Again, nice work.

Dan Johnson
(Seattle)

Locale: PNW
Frost King on 02/12/2012 19:04:03 MST Print View

John
Yes, I got all my supplies from Home Depot. The washers are just the cheap ones they sell in packs of 4 on aisle #24 and they cost a whopping $.64. When trying to find the Polycryo ask for the Frost King (the brand name) window insulation kit. It's around $7 for the 7x9 kit.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Polycryo Strength Analysis on 02/12/2012 19:08:11 MST Print View

"Did you source your polycryo from Home Depot? When I ask for it by name at my local "Depot" all I get is blank stares. If I ask for the clear window insulating film the stares continue."

Newton, my local Home Depot store doesn't stock those items either. It has to do with mild weather localities. However, you can order a package from Home Depot online. I think the plastic is 62"x210". Mine was delivered just last week.

--B.G.--

John Donewar
(Newton) - MLife

Locale: Southeastern Louisiana
Re: Frost King on 02/12/2012 19:08:59 MST Print View

Thanks D.

I see some experimentation of my own in the near future. ;-)

Party On,

Newton

Daryl Daryl
(lyrad1) - MLife

Locale: Pacific Northwest, USA, Earth
Re: Polycryo Strength Analysis on 02/12/2012 19:10:46 MST Print View

D Johnson,

Thanks for all your testing and taking the time to explain what you did and why.

I will definitely be using that imbedded washer idea for tie outs.

Perhaps the double sided tape could be used as tie-out material instead of the, as you say, overly strong gorilla tape? Hmmmmm, but how to deal with the double sided stickyness of it?

How about rolling the edge of the polycro into a hem with the double sided tape and an imbedded washer?

Daryl

John Donewar
(Newton) - MLife

Locale: Southeastern Louisiana
Re: Re: Frost King on 02/12/2012 19:11:24 MST Print View

Thanks Bob

I appreciate the info.

Party On,

Newton

Dan Johnson
(Seattle)

Locale: PNW
Washer on 02/12/2012 19:35:29 MST Print View

Daryl

I'm not sure if hemming the edges enough to sandwich the washer would work as well. The tape I used was 2" wide and allows for a greater contact area to dispurse the load. The polycryo may not be strong enough to have the small washer pulled against it for very long. But then again, I didn't test for that. Hmmm....

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Washer on 02/12/2012 19:39:42 MST Print View

Would it work better if the plastic washer was larger and thinner, and still held by tape?

--B.G.--

Dan Johnson
(Seattle)

Locale: PNW
Re: Re: Polycro strength analysis on 02/12/2012 19:42:30 MST Print View

Steven

Unfortunately I didn't measure the before and after lengths to determine how much it stretched. I just measured how much it stretched during loading. From my findings it seems that the Polycryo does show signs of post stress but that it was pretty minimal. I also can't say how much it returned to it's normal state after loading since all my samples failed.

Dan Johnson
(Seattle)

Locale: PNW
Re: Re: Washer on 02/12/2012 19:46:09 MST Print View

Bob

The washer was pretty thin. It could have been larger but this one had a hole in it that looked like the best fit for my guy lines. But if I could have found a thinner one I probably would have used it. I was thinking of making my own washers out of a plastic milk jug but I found these to be real convenient.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Re: Washer on 02/12/2012 19:52:33 MST Print View

"The washer was pretty thin."

It's time to get out your micrometer for measurements.

Yes, it is surprising how many things you can make out of milk jug plastic.

You can start by comparing the thickness of your washer to the plastic of a milk jug.

We might make a scientist out of you, but the chances are you will end up as an engineer.

--B.G.--

Ty Ty
(TylerD)

Locale: SE US
Washers on 02/12/2012 20:08:50 MST Print View

Bolts and washers, basically everything in the hardware aisle at Hime Depot and Lowes is really overpriced. I bet for a couple bucks at Fastenall you could get a pack of several hundred if not a thousand of those plastic washers.

Michael Ray
(topshot) - MLife

Locale: Midwest
Re: Polycryo Strength Analysis on 02/12/2012 20:10:04 MST Print View

> I guess what I can conclude is this. My original tarp used WAY TOO MUCH tape and the tie-outs aren't nearly as strong as they could be if I used washers. For all further polycryo shelters or anything I make with the material I think I'll "hem" the edges with the double sided tape as it showed it is stronger then without it.

Exactly as I figured. :) You can go with smaller washers, too, if you can find them. As I mentioned elsewhere, I don't use washers at all but make a loop of the tape only 7/16" wide to attach the guyline.

What I did not know yet was how the polycro would deform under tension so these tests were great for that. Thank you for taking the time. I'm surprised it stretched so much though I'm sure it's far less than the Heatsheets do.

I'm curious about the breaking point. Interesting that it always broke in the middle. Is it a clean or ragged break? I wonder if polycro has a bias. Could you repeat a test in a direction perpendicular to those you did?

I believe I read that polycro tears fairly easily. Have you tried tearing it on an edge?

FYI, the Duck brand is available at Walmart for $9 (last year) and is 7x10. I got them on clearance last spring.

Dan Johnson
(Seattle)

Locale: PNW
Re: Re: Re: Re: Washer on 02/12/2012 20:12:06 MST Print View

Bob

I can't seem to get my hotmail account working to upload photos (I always take photos from my phone and have to email them to myself and then upload them to my computer and upload them to BPL) but I can tell you that the washers are exactly the same size and thickness of a standard US penny.

Michael Ray
(topshot) - MLife

Locale: Midwest
Re: Re: Polycryo Strength Analysis on 02/12/2012 20:18:55 MST Print View

> How about rolling the edge of the polycro into a hem with the double sided tape and an imbedded washer?

That might actually work. One of the original versions George Geist did used brass grommets along the reinforced edges.

Tom Clark
(TomClark) - MLife

Locale: East Coast
Re: Polycryo Strength Analysis on 02/12/2012 20:33:13 MST Print View

I am a materials scientist and got my Ph.D. in "how things break," so I will tell you that you have done a very nice job in testing the materials and different configurations. Some additional tips...
- As someone else suggested, test in different directions. Film can have very different properties in the two directions. The diagonal (i.e., corners) can give averaged performance.
- Wider is better (tape, washers). Speading out the load will provide a lower local stress.
- Can you share some more photos of where/how the material failed? Understanding that helps suggest ways to make it stronger/lighter.
- Have you thought about doubling up the Polycro somehow (maybe some adhesive between layers). If there is a directional nature to the film, you could cross laminate the reinforcement.

That cross-linked polyolefin (polyethylene or polyprolylene???) is amazing.

Tom

Edited by TomClark on 02/12/2012 20:34:20 MST.

Dan Johnson
(Seattle)

Locale: PNW
Re: Re: Polycryo Strength Analysis on 02/12/2012 20:44:13 MST Print View

Michael:

Each sample test had a very clean break. And even more suprising was that each break was extremely perpendicular to the ground...

You asked for another test in the other direction. Would that mean that you would want a test to be performed with the tie-outs on the long side? Rather than the short side?

I have found recently that Heatsheets stretch far more easily then Polycryo. I haven't done testing on the Heatsheets but from how they feel when I try to pull them I would say Polycryo is stronger. On the other hand Heatsheets would give a lot more if a gust of wind came which could save your shelter. Polycryo would either hold strong or either rip violently. Kind of like carbon fiber.

@Bob

I went to school to be a Structural Engineer butI changed majors half way thru and always disliked science. I'll stick with the engineering side of things :)

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Re: Polycryo Strength Analysis on 02/12/2012 20:49:10 MST Print View

"Structural Engineer"

Remember what they say. Aerospace engineers make flying weapons systems. Civil engineers make targets.

--B.G.--

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Polycryo Strength Analysis on 02/13/2012 01:03:47 MST Print View

D. Johnson,

Really interesting analysis... thank you!

Just using engineering specs, the following appear to be the theoretical (smile) limits for the materials you are using:

Polycryo - (Standard Shrink Film) 12 microns thick yielding an average tensile strength of ~25.70 lbs. for a 3.00" strip and 28.40 lbs. for the 3.32" width that your photos indicate.

Gorilla Tape - Sold as 2" but, it averages 1.88 inches wide, yielding an average tensile strength of 94 lbs. for the linear inch of adhered surface on your shortest test sample.

Polycryo comparison to nylon - For the same thickness as your Polycryo (12 micron), nylon would be ~2.63x stronger.

1.1 oz. Nylon 6,6 + .25 oz. silicone coating (~480 micron typically used for UL backpacking shelters) – This conventional shelter material would be in the general ball park of 400x stronger.

Daryl Daryl
(lyrad1) - MLife

Locale: Pacific Northwest, USA, Earth
Making Things 101 on 02/13/2012 08:17:23 MST Print View

D Johnson

You and others (e.g. Michael Ray)contribute a lot of good info with these low cost but time consuming experiments. At $30 a yard for Cuben it is hard for most of us to be loose and creative with that fabric. Many of the lessons learned with the cheapo stuff apply well to working with the more expensive but stronger materials, however.

Thanks.

Daryl

Dan Johnson
(Seattle)

Locale: PNW
Re: Polycryo Strength Analysis on 02/13/2012 08:25:27 MST Print View

Thanks so much Richard for jumping on this thread to give your expertise! I was wondering what the tensile strength was for Polycryo and now I know thanks to you.

Since my test findings, I think I'll stick to making Polycryo tarps until I can either get the funds for some "real" material or I just happen to stumble upon someone looking to ditch their existing tarp.

It will be interesting to start seeing peoples experiments using polycryo in the field and not just for ground cloths. I can totally see this being a cheap way to add an awning or beak to a shelter. Or just close off one side of an existing tarp to protect from spray.

Michael Ray
(topshot) - MLife

Locale: Midwest
Re: Re: Re: Polycryo Strength Analysis on 02/13/2012 13:31:55 MST Print View

> Would that mean that you would want a test to be performed with the tie-outs on the long side?

That would be one way, but I would prefer if you were able to cut a piece of similar dimensions but in a perpendicular direction to those you used in your initial testing. That would eliminate any other variables except for a potential bias within the material.

Heatsheets do give quite a bit. Not an issue for most things except snow loading. I've determined to test that if we ever get any decent snow this year, but I suspect it would be significant.

I think polycro would work much better in that regard. It does give but not anywhere near as easily. I would not be concerned about the polycro ripping in the wind. Keep in mind you're loading only a thin piece of it vs an entire panel. It would eventually get to the point of failure but that will be very strong winds. It should easily take 50 mph if you have it fastened down well.

I'm curious now how mylar space blankets would fare in your tests. If Richard checks back, maybe he knows the tensile strength for that, too. I know those will tear catastrophically as well. I avoided using that material since it seems easier to poke than either LDPE or polycro.

> Polycryo comparison to nylon - For the same thickness as your Polycryo (12 micron), nylon would be ~2.63x stronger. 1.1 oz. Nylon 6,6 + .25 oz. silicone coating (~480 micron typically used for UL backpacking shelters) – This conventional shelter material would be in the general ball park of 400x stronger.

2.63 * (480/12) = 105.2 <> 400. Not being a materials scientist, is this discrepancy because tensile strength isn't linear with thickness of the material or that silicone somehow adds about 4x the strength to the nylon?

If I understand what you're saying here, Richard, if we assume 30 pounds to break the polycro sample, it would take around 12,000 pounds (30 * 400) to break a similarly sized piece of silnylon. I really find that hard to believe. I'd be amazed if it could even handle 3,000 pounds of force. If so I'd agree with that other thread the says our tarp materials are WAY too strong!

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Re: Re: Re: Polycryo Strength Analysis on 02/13/2012 19:37:15 MST Print View

Michael,

You said, "I'm curious now how mylar space blankets would fare in your tests?" - Theorectically they will provide ~6 lbs of tensile strength per in2 surface area.

You said, "...it would take around 12,000 pounds (30 * 400) to break a similarly sized piece of silnylon". If the nlyon was used in a monolithic sheet, the same thickness as the Polycryo, it would be ~2.63x stronger.

A conventional UL silnylon shelter is not comprised of a monolithic sheet but woven threads with a significant interstitial space and surface films comprised of silicone. In my original post I quickly ball-park estimated silnylon's woven tensile strength. I computed its relative thickness compared to the Polycryo (400x). That seemed plausible because high tenacity woven nylon strapping’s tensile strength reduced to the thickness of silnylon yielded (350x).

After your above question, I looked up the US government specs for type 1 and type 2 parachute cloth tensile minimum strength; they were 85 lbs. and 135 lbs. respectively. If we use these values as the low range estimate, then the 30D silnylon would have (9.9x to 15.8x) more tensile strength than Polycryo.

Michael Ray
(topshot) - MLife

Locale: Midwest
Re: Re: Re: Re: Re: Polycryo Strength Analysis on 02/13/2012 20:23:47 MST Print View

Thanks, Richard. That seems much more reasonable. However, I'm sorry to say I'm confused by your mylar figure now. Only 6 PSI?

Polycro is 0.5 mil apparently just like some mylars while the Heasheets are normally 1 mil. So if they are the same thickness, it seems that your figures suggest polycro has far greater tensile strength than mylar. Indeed it appears polycro is over 15000 psi while you said mylar was about 6 psi. A quick search seems that 27000 psi may be in the ballpark for a 50 gauge thickness, which I think is about 12 microns. Of course, there are a wide variety of mylars and cross-linked polyolefin so I have no idea which ones we are using.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Re: Re: Re: Re: Re: Polycryo Strength Analysis on 02/13/2012 20:40:08 MST Print View

Michael,

The Space Brand Emergency Blanket from MPI Outdoors is .00048" thick. The material is spec’ed, by the manufacturer, as having a tensile strength of 12,500 lbs./sq. in. So, (0.00048/1) * 12500 = 6 lbs. tensile strength per sq. inch surface area.

This is in contrast to the 8.75 lbs. tensile strength per sq. inch surface area for the Polycryo. Note that the standard Polycryo thickness is 12 microns = 0.000472440945 inches. The two materials are for all practical purposes, the same thickness with only a small difference in tensile strengths.

Edited by richard295 on 02/13/2012 20:49:38 MST.

ziff house
(mrultralite) - F
Why on 02/14/2012 00:19:32 MST Print View

Not forget about tie outs , I'll be making a cuben tarp with none . The tension will be taken by a dyneema thread sandwiched to the tarp and acting as a rope under the tarp. It may be necessary to reinforce the attachment of the ' rope' at the edges but most of the load should be taken by the 'rope'. This will be a simple tarp used as a cook shelter , but I'm sure more elaborations are possible.

Michael Ray
(topshot) - MLife

Locale: Midwest
Re: Re: Re: Re: Re: Re: Re: Polycryo Strength Analysis on 02/14/2012 04:21:44 MST Print View

Thanks for being patient with me, Richard. It seems an issue with units. I would have said that was 6 pounds per linear inch of the material, not per square inch since you multiplied by the area to arrive at that figure. I had assumed that's what you meant but you're known for being precise. :) I am surprised polycro is a little stouter in this regard. Seems an optimal shelter material for me except being transparent, which some might see as an advantage. Not an issue unless the moon is out.

Another experiment I'd like to do at some point is see how its properties change once it's been shrunk. Not sure what temp that takes but can't be too high since hairdryers work. I wonder if setting it in an oven at an appropriate temp would work or if leaving it folded would cause issues.

Dan Johnson
(Seattle)

Locale: PNW
Re: Re: Re: Re: Re: Re: Re: Re: Polycryo Strength Analysis on 02/14/2012 13:48:04 MST Print View

Michael

That's my next experiment with Polycryo. I want to shrink a known size (maybe 1'x1') and see how much it shrinks if I just leave the heat on it. Then I want to see what it's strength is under loading. I'm curious to see if it's more elastic then before. I guess there's only one way to know!

Dan Johnson
(Seattle)

Locale: PNW
Post Shrink Stress Test on 02/14/2012 23:45:02 MST Print View

Alrighty guys and gals. I had some time tonight so I thought I would do another test before I head to bed. I thought I would see what happens if a pre-shrunk a piece of polycryo and then stressed it.

Just to be super scientific I wanted to see how much this stuff shrinks under the heat of my wifes cheap-o hair dryer. So I set up a 1'x1' section and put it on the ground to shrink it.

test

Then I shrunk it (I removed the tape prior to shrinking FYI)

test

After about 4 minutes this is what it looked like. It shrank almost exactly 2" in both length and width. Making it 10"x10".

Then I took a test strip and put it to the test. You can see from the photo that the polycryo really doesn't shrink evenly. I had my doubts testing it cause it looked like one side of the sample seemed to shrink more then the other. But the test most go on :)

test

As I loaded the sample I noticed it stretching pretty quickly. More so then the orignal non-shrunk samples. This stress test showed that the shrunk sample failed at about 22 lbs. Far less then the original non-shrunk 30lbs.

Here is a close up of the sample where it failed. This is what every sample looked like after it failed.

test

Also, just in case anyone was wondering. These are the plastic washers that I am using.

test

Edited for spelling

Edited by Seattle on 02/14/2012 23:47:48 MST.

Michael Ray
(topshot) - MLife

Locale: Midwest
Re: Post Shrink Stress Test on 02/15/2012 07:47:54 MST Print View

Cool. So it's not be as robust after being shrunk. Good to know, but can't say that I'm surprised.
It's possible it may weaken over time (exposed to hot sun), but doubt that would be significant. I think I'll devise a test for that once summer hits.

It does look kind of funny after it's shrunk without being held down, doesn't it?

That is a nearly perfect tear. Have you had the chance to test a perpendicular sample yet?

Edited by topshot on 02/15/2012 10:47:11 MST.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Post Shrink Stress Test on 02/15/2012 09:09:19 MST Print View

D. Johnson,

Thank you for the continued analysis... really interesting!

Edited by richard295 on 02/15/2012 11:01:20 MST.

Daryl Daryl
(lyrad1) - MLife

Locale: Pacific Northwest, USA, Earth
Re: Post Shrink Stress Test on 02/15/2012 10:52:09 MST Print View

This is soooooooo much more interesting than watching tv.

Thanks again for the show.

Harald Hope
(hhope)

Locale: East Bay
more complex load spread? on 02/15/2012 11:41:17 MST Print View

D Johnson, since you're in the testing groove, I'm wondering if you would want to test a more complex tieout, say, a star shape of tape, say, 2 or 3 pieces, at angles to each other.

The failures you are getting are almost identical to the way cuben failed in a test of catastrophic failure:
http://www.suluk46.com/documents/Suluk%2046%20-%20A1%20-%20Testing%20Cuben%20Tieouts.pdf

ie, it rips right at the flat edge where the force of the stronger material meets thee weaker.

I'm curious what happens if those flat edges of force get changed to angled edges, if you know what I mean.

Polypro like stuff I think can be used for some applications, and it's a lot cheaper than cuben.

By the way, Ace hardware has rolls of this stuff, Bulk Shrink Film, item number 5069190, 25 feet by 62 inches. Cost about 12 dollars.

Not sure how many mils it is, probably the same as the other window insulation films.

ziff house, I'm intrigued by your dyneema tie out idea, can you give more details, or pictures? I got some cuben from lawson at his cuben sale with the very same thing in mind, a kitchen/ rain cover tarp, but I have been waiting to make it due to the cost of the material, want to get it right the first time. Since it's an addition to the winter setup, not a sleeping tarp, I want it as light as possible, and as simple.

Edited by hhope on 02/15/2012 11:47:25 MST.

Gregory Petliski
(gregpphoto) - F
re on 02/15/2012 12:08:42 MST Print View

WOW I was just thinking of this, and came here to post about it.. glad I saw this first!! So have you done the most important test yet.. using it on a rainy night in the woods? I'd be super interested to know the results. I've heard this material can really take a beating, and at $6 for a 6x8" piece of it, if I get two-three months out of it (of everyday use that is), I'm happy. I read a review from someone who used a single sheet as a groundcloth for an entire PCT thru hike, that really says it all!

Dan Johnson
(Seattle)

Locale: PNW
Re: re on 02/16/2012 23:05:04 MST Print View

Gregory:

I haven't been able to find the time to take it out in the woods and play with it but I've had it setup at my place for a while now and it's seen its fair share of wind (more like breezes) and rain (lots of rain). It's held up really well. I'm not sure if I said it earlier but I only "need" this tarp to last about 10 nights worth. That is the most I will do in two years so I don't need something that will last longer than that per say. Who knows, maybe I'd want to go back to tents and this way I'm not out a bunch of money. But, so far I think I've found something that really works for me and could work for probably a bunch more. The key is just to know the limits.

Gregory Petliski
(gregpphoto) - F
re on 02/17/2012 09:24:45 MST Print View

@D Johnson: It should in all fairness last a lot longer than ten nights on the trail, right? As tough as this material seems to be, I'd be surprised if I couldnt get months of continuous use of it. I have plans to make a custom shelter out of polycryo, will post pics when I do. Thanks!

Daryl Daryl
(lyrad1) - MLife

Locale: Pacific Northwest, USA, Earth
I agree on 02/17/2012 09:32:42 MST Print View

"The key is just to know the limits"

D,

I agree with your comment. I want to have a good idea when something is going to break, tear or come apart. I can then add a margin of error or prepare for the eventuality of the failure in the most weight/cost effective way. Your tarp is perfect for this because we all know it is at the very edge of failure now or in the eventual future. But when will this failure occur and what will be the weakest link that gives first? Inquiring minds want to know. For me it is like watching a serial movie.

The area where I've gone the farthest with this "testing the limits" strategy is my myog backpack. I keep going lighter and lighter on my way to the eventual breaking point. The fabric, for example, has gone from 6 ounce pack cloth to 1.9 ounce nylon to 1.1 ounce nylon with no failures yet. Next version will be out of M50 nylon which weighs about 3/4 ounce per square yard. Regardless of the outcome I've already concluded that most packs are way overbuilt fabric wise. Most of us aren't scrambling over abrasive granite or running through thorn bushes.

Keep up the good work. I've purchased a season ticket for your adventure.

Daryl

Ty Ty
(TylerD)

Locale: SE US
Fastenall on 02/17/2012 09:36:18 MST Print View

Just as an example of how expensive Lowes and HD are on stuff like those washers...

This is probably not the same washer exactly, I can't tell what the ID of that washer is but here is something not too far off at Fastenal...

http://www.fastenal.com/web/products/detail.ex?sku=11107626

They are $0.042 cents each so 100 of them would cost $4.20 cents. Lowe's and HD probably charge $1.99 or more for 4 of them. My brother and I build 4x4's and we use a lot of grade 8 bolts. The first time we discovered Fastenal we realized that for the cost of 1 grade 8 bolt at Lowes and HD we could typically get 10-25 of that same bolt at Fastenall. Some of the smaller stuff at HD and Lowes that came in bags of 2 with the nut and/or washer we could get 100 of the same thing at Fastenall for the cost of 2 bolt/nut/washer combos at Fastenal. It is ridiculous what they charge you in the hardware department at big box home improvement stores. Heck most everything is way too high. I have found the same thing with a lot of their chemicals like insect stuff where you pay X for one small can with a couple ounces of X spray and you can get a 20 gallen drum of the same stuff at a do it yourself pest control store for the same price.

(rant over)

Paul Johnson
(johncooper) - F

Locale: SoCal
How long will it last on 02/17/2012 10:18:37 MST Print View

Regarding length of time until failure. I recall another thread or article saying the tie out tape will slip from the tarp fairly quickly (ie less than 7 days). The solution was to put some staples through the tape. This could also be a difference when using Gorilla tape.

DJ you are an inspiration. I'm a tent sleeper and this thread has given me a method to experiment with a tarp.

Michael Ray
(topshot) - MLife

Locale: Midwest
Re: How long will it last on 02/17/2012 10:30:40 MST Print View

> Regarding length of time until failure. I recall another thread or article saying the tie out tape will slip from the tarp fairly quickly (ie less than 7 days). The solution was to put some staples through the tape.

Staples? I'd never do that. Tape should be fine if you use something that is UV resistant. Gorilla Glue tape seems to be. 3M TRANSPARENT Duct tape is. Normal duct tape is not.

Ty Ty
(TylerD)

Locale: SE US
Re: How long will it last on 02/17/2012 11:05:50 MST Print View

You could sew the perimeter of the duck tape then seam seal it maybe. Might be overkill.

I really liked the idea of sandwiching the washers between a folded hem on the edge of the tarp. I would be curious to know how the strength would compare. Possibly with a glued hem.

Michael Ray
(topshot) - MLife

Locale: Midwest
Re: sewing duct tape on 02/17/2012 11:30:12 MST Print View

NOT a fun experience. :) Really gums up the needle so you need to clean it about every foot. I had tried to do my shelter totally without sewing. That is easy without netting, of course. The tape wouldn't hold the netting though so I sewed it on. My next test with netting will use silicone or an adhesive to bond it to the LDPE or CLP.

Daryl Daryl
(lyrad1) - MLife

Locale: Pacific Northwest, USA, Earth
More Options/Testing on 02/17/2012 14:39:59 MST Print View

The taped washer inspired me to try this as an option.

here

here

here

The photos above show a 2" wide piece of clear Frost King tape folded over at each end 2". One end has no reinforcement. The other end has a small .3gram piece of vynal from a notebook enclosed within the tape. A hole was then punched in each end with a paper punch. When I hung weights from the item the unreinforced end tore with 14 lbs of load.

I then made a new piece of tape with reinforcements at each end and tested it. The reinforcements held but the tape started elongating at about 19 lbs. Ended test. Photos below.

here

here

Conclusions

Washer or washer like reinforcement is very effective. Same conclusion as D. The technique I used could be used with any piece of stiff plastic scrap that one has. No need to buy washers.

Edited by lyrad1 on 02/18/2012 07:54:39 MST.

Gregory Petliski
(gregpphoto) - F
re on 02/17/2012 14:57:14 MST Print View

Just wanted to make a note on the weight of the Gorilla Tape. According to the manufacturer, the 2" wide roll weighs about 0.66 oz a yard, and being such a tough tape, I'd take the ever so slightly heavier weight knowing that your tape ain't going anywhere.

Edited by gregpphoto on 02/17/2012 14:58:31 MST.

Dan Johnson
(Seattle)

Locale: PNW
Re: re on 02/17/2012 16:57:01 MST Print View

Thanks for getting the weight for the tape! Now I can calculate even more...

I did the math with those numbers for the gorilla glue for my tarp and it seems that I used about 84" of tape @ .66oz a yard equals about 1.539oz. When you put it that way it doesn't seem like very much weight at all, but it does seem like a heck out a lot of tape!!!. I mainly notice it when trying to pack it up. The tape doesn't bend very well once folded over and it makes the tarp much bigger when trying to store it after use.

After my strength analysis I now can determine that I'll only need 52" of tape. That makes the total tape weight drop to .953oz which is a 38% reduction in weight if my math is correct.

Phillip Colelli
(pdcolelli42)

Locale: AT, follow@ www.thruperspective.com
wish I saw this sooner! on 02/25/2012 17:30:21 MST Print View

Wow, I've read other threads here recently on the polycro tarp you've made. Love the idea! I have a couple ideas on what to do with the polycro I got form home depot a few weeks ago.

I'm thinking I'd like to make either a bathtub floor groundsheet for use with y poncho tarp so I can pitch it higher during rain. Or I'd like to make a beak for use with half pyramid pitching. Maybe it would be possible to combine the two idea to create a bathtub floor groundsheet with a long flap on one of the sides that could be tied up for rain protection. That probably makes no sense to read... but I guess I'll just have to try to make it and post pictures in a new thread one day.

Thanks everyone who contributed to this thread. Very useful stuff!

Dan Johnson
(Seattle)

Locale: PNW
Go to target on 02/26/2012 02:12:13 MST Print View

Just in case anyone wants to know, I found that target was selling patio door insulation kits for only $2.98 in their clearance section. It's now even cheaper to build something out of this stuff!!! I bought a couple just cause I couldn't say no to the price :)

Michael Ray
(topshot) - MLife

Locale: Midwest
Re: Go to target on 02/26/2012 11:40:35 MST Print View

That's even better than the $4.50 clearance ones I got at Walmart last spring!

Here There
(cowexnihilo) - MLife
Washers on 02/28/2012 08:32:50 MST Print View

A quick note for anyone attempting one of these, make sure the washers you use are robust enough. I was going to use pieces of a milk jug since that's what I had on hand, but in testing some tieouts under repeated stress the cord cut through the milk jug washers and gorilla tape.

In short, use tougher plastic or the store bought washers.

-David

Steve B
(geokite) - F

Locale: Southern California
Curious on 02/29/2012 15:57:42 MST Print View

Anyone have any pictures of a tarp from polycryo? Size of tarp and weight?

Steve

Michael Ray
(topshot) - MLife

Locale: Midwest
Re: Curious on 02/29/2012 16:27:59 MST Print View

Searching does wonders

Steve B
(geokite) - F

Locale: Southern California
Thanks! on 02/29/2012 16:34:33 MST Print View

Thanks!! I'll be sure to search before any reply in the future!

Steve

robert van putten
(Bawana) - F

Locale: Planet Bob
Thickness? on 02/18/2013 15:22:29 MST Print View

"Note that the standard Polycryo thickness is 12 microns = 0.000472440945 inches"

Wait..What?

Where the heck does this "standard" come from??

.47 mils is standard?
Seems like extra thin stuff to me.

Dennis brand window kits say .6 mils for the interior stuff ( 15.24 microns ) and 1.2 mils for exterior film ( 30.48 microns ).

I can't tell how thick the Frost King kits are, but have found one reference on their web site that mentions outdoor kits with 1.25 mil ( 31.75 micron )film.

Dan Johnson, what source are you using for the stuff you are testing, and what is everyone building their tarps from, the thin indoor kits or the possibly twice as thick outdoor kits?

( Edited because I got my darn decimal point in the wrong spot)!

Edited by Bawana on 02/18/2013 15:25:41 MST.

Dan Johnson
(Seattle)

Locale: PNW
What I'm using... on 02/18/2013 22:36:40 MST Print View

I'm using the Frost King Interior large patio door kit.

robert van putten
(Bawana) - F

Locale: Planet Bob
interior stuff!? on 02/19/2013 13:02:12 MST Print View

I'm surprised!
The thin interior stuff is stronger than I figured it would be.
I can't help but wonder how strong the probably-twice-as-thick exterior kits are.