Cuben – The 422 mm hydrostatic head dirty little secret

Hi Matthew:

I will let you know about follow up.  I need to change the means of delivering pressure to the device so that higher test pressure can be achieved, at least to 20000 or, ideally, 30000 mm/wc.  I think it will be easy.

Concerning the aging.  It is a simple process.  The sample is placed in a washing machine for a single cold wash cycle.  It is then dried at ambient in the dryer.  I have no idea what that corresponds to as far as actual use goes.  I am curious about what happens to this material when a tent is packed away in a stuff bag multiple times–does the fabric become as wrinkled at the aged test sample shown in the photograph I attached?  Do the wrinkles disappear after the tent is erected?  I can diminish the wrinkles on the aged sample simply by pulling on sections of the fabric.

The washer/cold dryer technique seems connected to cycles. With switches, how many thousands of times can they be flipped before a certain percentage begins to fail. It can be tens of  thousands of cycles for a residential wall switch to millions for something industrial (Ikea lamp cord switches? 10-20 times).

With something flexible they usually bend it back and forth, sometimes with a bit of a yank. Fabric may seem like it has a near infinite flex but there are limits and someone has probably measured them.

Based on what I know about cheap plastic tarps, sun exposure and wind. I wrapped a mattress set in a brand new blue plastic tarp, tied it to the roof of a pickup, and drive it from NYC to L.A.,CA By Utah the edges where shredded, by L.A. the middle had tears.  So a very windy night  to tent fabric is probably a very significant amount of wear. Stuffing it? Probably not much at all. The material is relaxed, the strain is mostly in the stuff bag and your arm.  All of this is mostly idle speculation.

So a very windy night  to tent fabric is probably a very significant amount of wear. Stuffing it? Probably not much at all.

Our testing and experience is that stuffing is the most stressful thing you can do to Dyneema.  Stuffing applies greater unequal forces to the Dyneema laminate layers than wind forces and it’s the inequality that does the damage. Over time/repeated stuffing, the forces tear apart the laminate from the inside out.

-H

Thanks for the correction. I had no idea.  Maybe DCF should be rolled up? (Maybe I better quit while I’m behind).

I have modified the HH tester.  It is now, in principle, capable of measuring up to 30000 mm/wc.

I tested one new sample (unaged). At 21706 mm/wc water leaked around the clamping ring.  No drops occurred in the test area.  I would say that the HH is therefore well above 22000 mm/wc if you use a tester with a better clamping ring design.  For the aged sample, water leaked around the clamping ring at 19850 mm/wc.  No drops appeared in the test area.

Henry S:, perhaps you might have a feel for whether any further testing is worth completing.  Do you think that the aging process stresses the fabric sufficiently?

Henry S:, perhaps you might have a feel for whether any further testing is worth completing.  Do you think that the aging process stresses the fabric sufficiently?

My take is that the value of testing comes from establishing what will happen before it happens in the field and testing field stresses are what matters.  Packing (folding, rolling, and/or stuffing), sun and wind and rain exposure, point stresses (intense wind gusts, tripping over guylines, pitching on rocks etc.) are expected field use stresses and to the extent they can be sped up and tested then testing is beneficial.  Pressure rating drops over time on all fabrics but what matters (and is testable) is the point at which the fabric no longer resists expected pressure from rain and wind (and kneeling).  In our testing, pressure rating on 0.51 and 0.74 Dyneema starts to fall off dramatically after the 2nd agitating machine wash and would no longer quality as waterproof enough for a really hard rain but the question is how that sort of stress compares to a long term field use.  I contend that stuffing is much closer to the kind of stress than gentle rolling.