doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Blow Up EUREKA

An incredibly illuminating time with Adam at METL, who has an interest in damascus/wootz blades and has visited Al Pendray's shop in Gainesville.

Boy was I/most of us confused

1. This is rivelling from plastic deformation during the rupture - NOT the crolle pattern. I think Will & Craig called this one



2. Adam, on initial examination, did NOT identify low cycle fatigue but suspects an area of embrittlement at the forward, lower point of the blow out. He agrees the deformation superiorly looks like there was a bulge.



3. Unfortunately, composition testing by EPX, SEM, or OES will require a piece of a Damascus demonstration rod at least 1" X 1" and with the layers of steel and iron at least 1/16". The dense matrix of iron and steel will not allow analysis of each component separately. SO if someone would please whack off the end of their demonstration rod, we could do the testing, then try to match each with the modern equivalent



4. Photomicrographs of the barrel wall should give us a definitive diagnosis, AND identify interlaminar rust, voids, inclusions, micro-fractures, defects. Adam does NOT think the fracture lines follow weld lines.

5. Adam does not believe MPI/Magnaflux testing would be the best procedure to identify defects in the barrel walls by NDT. Gloria a Dios there is another testing lab in Phoenix that specializes in radiographic (x-ray) testing of metal and I will set up a meeting with their engineer.
I'll have two barrels for radiography; one of which could then be sectioned to identify any defects found on the x-ray testing and possibly blown up to see if the blow out occurs at the defect.

Adam shares my excitement about doing something no one has done before, and I am hopeful that the x-ray testing (of course combined with wall thickness, chamber, and bore evaluation) may be a way, and at less cost, to establish a GREATER (but not definitive) level of confidence in the safety of Damascus barrels.

Again, many thanks to all who have contributed opinions and suggestions!!

Thanks Drew.

I hope that part about embrittlement is not the case, as this would pertain to all old guns Damascus or fluid steel.

ninepointer brought this up earlier.
"Something I've never seen discussed at length is, notwithstanding adequate wall thickness etc., can metal fatigue be an overlooked factor in old doubles? Metal fatigue is usually not detectable to the naked eye or through caliper measurements. Yet military research (albeit that research has been mostly done on very, very big guns) has clearly established that metal fatigue in such guns is real and that the safe and useful life of a gun has its limits, even if that gun was always operated within its design specs. Formulas have been developed to predict when a military gun needs to be taken out of service."

How does the overpressure that was indicated by the extractor imprint on the steel base of the hull figure into this explanation?

I need to know how embrittlement and plastic deformation would not be mutually exclusive.

My working hypothesis, and feel free to post yours:

1. An unknown (and likely never known) something obstructed the bore
2. Pressure rose proximal to that obstruction.
3. The rise in pressure caused a bulge, which caused the rivelling.
4. The rise in pressure caused the expansion of the base of the hull's steel head, and the extractor left an imprint on the head (both described by Burrard)
5. When the capacity of the chamber/barrel proximal to the obstruction to contain the pressure was exceeded, the barrel blew (in at least 2 pieces but NOT along ribband weld lines), possibly starting at the area of embrittlement.

IF METAL FATIGUE IS PRESENT, microphotographs will show evidence thereof. Adam described it as the appearance of the sand at the edge of the shoreline ie. layers of wavy lines.

Although highly unlikely the obstruction may well have resulted from "shot bridgeing" where for some reason the shot was fused togeather and did not compress when it passed through the forcing cone perhaps caused by hot gas escaping around an ill fitting wad.

Good stuff Doc Drew. Was there any comment about the appearance of the grain of the steel. I'd guess that the same steel with a finer grain would be tougher and more resistant to failure. Any comment about possible preexisting defects, maybe the bright metal of the sudden failure is different from the occasional small pockets of dark appearing maybe oxidized pits that may have been there from before the mishap.

Any thoughts as to why the barrel appears as though pressure vented in a limited area and doesn't appear to show 360* signs on the inside of the barrel. I'm only being curious, and thank you for looking at it a whole lot closer than these things tend to be.

I agree with all 5 points, except the part about brittle.

The metal shows ample evidence of elasticity in the bulged part.

I eagerly await more information Drew. I'm not a metalurgist I'm a drunkard, which at least according to Captain Renault makes me a citizen of the world.

SGJ: I edited the original post for clarity. Again, initial visual examination did NOT suggest low cycle fatigue.

"IF METAL FATIGUE IS PRESENT, microphotographs will show evidence thereof."

Ah!

So there's no presumption of a fatigue condition.

Maybe it was the 'low cycle' thing that wasn't in my lexicon.

One would naturally think 'high cycle' might be the appropriate term, but specialists tend to use cryptic terms.

I'll edit my post so I don't look like I completely lack reading comprehension.