Photos from Dan's GH 20

[edgarspencer]

Originally Posted by Dean Romig

Letting the science do the talking, those “striations” could be simply the result of lateral stretching of the metal.

The term for "streching" is Elongation; one of the four basic maesurements obtained in a destructive test bar. Tensile, sometimes expressed as UTS, Ultimate Tensile Strength, Yield Strength; the point at which the specimen will no longer relax to it's original length (2") RA, Elongation, as a percentage of the pre-measure 2" measured length, and lastly, Reduction of Area, the amount the specimen reduced at the point of failure. The area at the failure of the test bar has a somewhat different appearance, dependent on the alloy, but looks nothing like those 'striations', which, in my opinion, are on the surface. I also doubt there was any linear stretching, simply because the failure area reach (1st) Yield, then UTS and elongation.
A properly heat treated specimen fails in a very predictable, and repeatable manner; the numbers only varying because of the percentage of individual alloying elements.
On average, we produced between 25 to 30 individual heats (Furnaces batches of steel) per week, and it's safe to say we would break between 6 and 20 tensile specimens per heat (not to mention creep strength tests, Charpy (V notch)Impact tests, and weld bend tests)

Originally Posted by ED J, MORGAN

That seems logical as the metal expanded the radius on the out side being greater than the inside would tear first,

You are quite correct. The area of the failed tube is the CxOD minus the CxID.

Originally Posted by Pete Lester

I am not engineer and have no experience or training in the physics and engineering involved with a barrel burst. What I find counterintuitive as a layman is the amount of pressure required to burst a fluid steel barrel is around 30,000 psi per Sherman Bell's destructive tests. How is it that a shot charge and wad being pushed by a force between 11,000 and less than 30,000 psi wouldn't dislodge and send a thin plastic base wad stuck in the bore out the muzzle before it reached a level of barrel burst pressure? Serious question looking for an answer. Perhaps the answer is the pressure builds faster than the ejecta moves but I don't know that.

Bell's burst tests were on unobstructed tubes, and, I think This tube was obstructed, and in pretty close proximity to the charge. The spike was (obviously) catastrophic. The pressures rise initially, after firing, and decrease the further down the bore they are measures. Within a few inches of the forcing cone, they're going up fast, but with no bore to go down.

I remember some work done by a Proof House, that took deliberately sealed tubes of various lengths, and measured the resulting failures. I found it while in the library at Leeds University, no doubt waiting for the pubs to open on a Sunday evening. That was an exchange year from RPI, and despite learning a lot, found the pubs dramatically more interesting than the labs.