Other than the test video, without any instrumentation, post test hardware
inspection (and speculation) will be all you can do to conduct your
analysis.
One channel minimum of Pc, chamber pressure, trace would be helpful. Even
an analog pressure gauge on video would give
at least a low frequency reading and maybe give the failure pressure...
Posting some pics of the post test hardware would give more eyes on the
subject and more chances of zeroing in on the overpressure mechanism.
Ken.
On Tue, Feb 21, 2023 at 8:25 AM John DeMar <jsdemar@xxxxxxxxx> wrote:
Rick,
From those specs on the case and screws, I get about 2800 PSI to shear
the screws (derate grade 8 tensile strength by 50%). Assuming 1/4" wall
standard-grade oil pipeline steel, the case should have deformed the holes
at 2000 PSI and sheared at 2400 PSI. High grade pipeline steel would shear
at 3000 PSI. I didn't derate for temperature based on the short time to
heat soak.
So, plenty of margin on the hardware for a normal operating pressure in
the 1000 to 1500 PSI range.
-John DeMar
Las Cruces, NM
https://www.linkedin.com/in/jsdemar/
On Mon, Feb 20, 2023 at 7:18 PM Rick Maschek <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
The case was approximately 12 inch by 9 feet long, quarter inch wall oil
pipeline steel pipe.
24 grade 8 half inch bolts in two rows holding the quarter inch wall
steel retaining ring.
The forward bulkhead was a steel plate welded in the motor case.
5 grains of KNSB propellant 20 inch long with the cores varying from 2.5
inches at the bulkhead to 4 inches at the nozzle
We used aluminum motor cases as our mandrels covered in silicon sheet
and greased for release.
The nozzle grain weighed in at 124 pounds with the others slightly
heavier because of smaller cores.
The nozzle had a 94% ideal density, normal density for me is 96-98%
I was up all night Thursday and much of Friday night helping student
teams so I left soon after our 12 inch test.
Not sure what caused the anomaly, lots of speculation and guessing. I'm
still investigating the cause.
We had two previous successful 12 inch KNSB sugar tests, one with 2
grains and one with 3 grains.
This test had five grains and was designed to be progressive to test our
three piece safety nozzle.
Design pressure at start up was higher than the two previous 12 inch
tests.
Flew a 4 inch KNSB motor just a couple hours before the 12" test UCLA
Rocket Project Avionics & Recovery test
<https://www.youtube.com/watch?v=jWspWbTCXbM>
UCLA Rocket Project Avionics & Recovery test
<https://www.youtube.com/watch?v=jWspWbTCXbM>
https://www.youtube.com/watch?v=jWspWbTCXbM
Rick