Sunday, May 31, 2015

Quick tank update...

The goal for the composite tanks are 250PSI operating 500 psi design burst and 375psi qualification.
Today the tank I tested failed at 375psi.  When I blew one end out, I did not re-bond the opposite end, the opposie end then failed. (Sort of expected)  When it failed it also split lengthwise.

John is gong to make me some new tubes to test.. with a peel ply layer at the bonding ends and an additional layer on the ends for additional strength on the end caps.
We may add enough material to have bolted ends as that allows you to disassemble and inspect etc...

I also need to slightly rework my seals as the tank seeped until the pressure came up and the seals seated hard. (IE it seeped at 50psi, but stopped at 125 or so)

The current conceptual launcher uses bundles of 4" tanks so the next tube samples will be 4" The current sample is 3"

9 comments:

George Katz said...

Hi Paul,
We make our CF pressure chambers using a carbon fiber sleeve (from Soller Composites) over a lightweight thin walled fiberglass inner liner that's assembled from sections. The bulkheads are integrated into the design.
Here are some more details of the construction:
http://www.aircommandrockets.com/dark_shadow_1.htm and
http://www.aircommandrockets.com/dark_shadow_2.htm

We use these at 650psi, although they are only 63mm (2.5") in diameter. We choose the sleeve size so that when it is stretched onto the liner the fiber direction is close to the optimal winding angle of 54.7degrees for maximum strength. While the fiberglass may not be chemically compatible for what's going into it, you may be able to internally coat it, or just use a poly bag on the inside.

Cheers

- George

Paul Breed said...

What was the volume and weight of your darkshadow tanks?
Cool project BTW...

George Katz said...

The volume was 6.77L and weighed ~980grams. We didn't vacuum bag it, and only used peel ply to remove excess epoxy. I believe with vacuum bagging you would get better results and reduce the weight by another 10-20%. The wall thickness of the fiberglass inner liner was about 0.4mm.

For lower pressures though you could get away with a lighter sleeve, or same weight sleeve and bigger diameter. (We used the 12K heavy - http://www.sollercomposites.com/composites/carbon%20fiber%20sleeves.html)

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