For instance, both tubes were prefabricated and then the Hysol was applied to one or both surfaces and the parts were mated...did you find any particular adhesive gap was best?
Yes to all of the above... we fabricated the tube and bulkhead, then bond prepped & applied Hysol to the bulkhead surface, and finally cured the piece. The challenge was maintaining a consistent bondline thickness around the part. Hysol's shear strength is guaranteed for a certain thickness, no more, no less, and so we made extra efforts to keep everything concentric and ensure an even distribution of adhesive.
The important parts of the bond are the bondline thickness, and the bond prep. We use an acid etch method similar to that described by Anthony.
Also, regarding the hydrostatic testing, did you do this at school and if so, what sorts of barriers did you run into with faculty and stuff?
For hydrotests, we go out behind our lab building into the dumpster-bunker (you know... one of those cinder block-walled places that they keep dumpsters that looks like it could withstand nuclear war, sans roof) and test in there. There happens to be a hose hookup nearby, and our hydro pump isn't too heavy, so it's no big deal to carry around. Since there's very little energy involved if the part in question fails, we haven't had any issues hydrotesting on campus.
I guess the question really extends to motor-experimentation as a whole... one of my professors is just about done getting an LEUP though we still have to convince the other professors that we wish to pursue motor-fabrication seriously...and not play around. Any suggestions?
Get your California Pyrotechnic Operators license. You can start directly with a Class 2 license for working with solids, and then move later to a Class 1 license for liquid work. When firing, we operate under the supervision of multiple pyro ops at the MTA. And we document *everything*. This gives the impression that we are serious about what we do... and most of the time, we are!
Technically, there is no motor size restriction on this site besides the california M motor thing (I assume that rule still exists)
If you are operating under the rules for "experimental rockets/unlimited", to the best of my knowledge, there is no impulse limit. (*I might be wrong on this, but 19 CCR § 1010-1019 seems to agree with me). However, the ER/U rules are a bit stricter than for simple high power motor tests and flights. We've flown motors larger than the 2300 lb-sec M limit with no problems under ER/U.
What about the thermal cycling problems that may occur with the aluminum/CF composite? When heated the aluminum will have more thermal strain and a stress will be induced on the joint. Has this been a problem in the past?
We're still waiting to make it through an entire burn to find out ourselves
It's an interesting challenge trying to prevent the case from leaking. I think we've got the problem licked, though, so we're gonna try again in May...
are you using the wax method for filament winding?... For what I understand, it may have to do with non-uniform stress distribution so local fiber groups fail and move to the next group and those fail and so-on. I dunno.
We convolute wind our tubes from unidirectional Cytec prepreg. Your theory about local failures seems to be correct based on our testing, however we have designed the tubing with such a safety margin that small failures of the fiber matrix are of little consequence to the pressure capabilities of the tube. During hydrotesting, we often hear the tubes creak a bit as assorted fibers fail; even testing the same section multiple times to over 2000 psi, we've yet to blow a tube up.
