Is this a shot test

[gordon]

A Brinell Hardness Number ( BHN value ) will give you a decent measure of ballistic penetration resistance up to about 3/8" thick plate, since I'd expect an impression made by a 10mm Tungsten ball.

Over about 3/8" thickness, and depending on the plate production method, the physical characteristics of the metal at the centre of the cross section would be such that a BHN figure would just be a guide, and some chunkier form of testing would be required.

If I was setting it up, I'd have the plate subject to a a drop test, where a known weight was dropped on it from a known height on a particular shape and cross section of pin. It would be reasonably easy to simulate the energy input and physical characteristics of a bullet that way, and the resulting dent would look fairly similar. The result wouldn't be recorded as a pass or fail either, you would record the displacement ( depth ) at the centre of the dent, and make a separate note of any physical damage such as cracking or penetration.

Test frequency would be one or more per type of plate per heat treatment batch and per cast number ( distinguishing between the cast number, which sets the chemical composition, and the heat number, which sets the physical heat treatment characteristics )

If I had to guess, on the 81047 image above, I'd say that someone has done a drop test on the plate, and then a Brinell Hardness at the centre of the drop test mark, probably to generate consistent records as you would know both figures came from the same area of the plate.

If I had to fake up a test report;

Date: 01/01/19xx
Tester: MLU
Cast: ABC123 Bloggs Foundries
Heat: DEF456 Smiths Heat Treatment
Plate Batch: 81047 Production side plate, 5/16" thick
Impression Depth: 3/32" from 50lb load dropped 3 feet on 1/2" standard pin
BHN: 235 using 10mm Tungsten indenter at impact centre.
Notes: No evidence of cracking or penetration

[motto (RIP)]

Around forty years ago I was involved in a discussion about what would and what would not penetrate a carrier hull in the way of small arms fire. This came about because there was an abandoned, stripped out, hacked around carrier hull laying around on a property where my workmates used to hold occasional social functions (read 'booze-ups').

It was decided that the only way to settle the argument was to carry out some practical testing. Subsequently a return was made to the site in the cold light of day and all of us completely sober with a selection of firearms and ammunition. Firing was at right angles (square on) and carried out at a range of 30 to 40 feet with the impact area being on standard thickness hull armour ie not frontal. To the best of my memory the findings were as follows:-

.303 Mk 7 Ball - A bit of a dent, bullet vaporised.
.577/450 Martini Henry - A shallower dent, bullet vaporised.
.303 AP (don't recall Mk No) - Consistent penetration of tungsten carbide core.
30-06 AP - Inconsistent penetration of hardened silver steel core. Core break-up.

Nothing we had would penetrate the frontal armour.

The dimple in Michaels picture is nothing like a bullet strike, either AP or Ball. The edges are too defined.

David

[Lynn Eades]

Thank youMichael, Hanno and Gordon, for you detailed posts.
Here is the rear flap from a 1938 Bren NoII, MkI, (HMH243) The two indentations would fit remarkably well the descriptions given in the last two posts, re the Brinell test.

[Richard Farrant]

The Daimler armoured vehicles made during WW2 had a much more accurate hardness test and done with a very small ball probably only a few millimetres in diameter. Every armour plate had a small area surface ground, approx. 15mm square and the ball mark within it. This way the indentation could be accurately measured for depth. Not sure if this was Rockwell or Brinell method now, without checking.

[Michael R.]

Did I cause a misunderstanding in my previous post? Regarding the image of the numbered armour plate with dimple and straightening hammer tool mark impressions: I am quite confident this dimple tool mark impression was made following the heat treating process, and that it was done by a method similar to the Brinell or Rockwell testing protocol. This same plate has these test marks at regularly spaced intervals. It has nothing to do with a rifle cartridge bullet being fired from a barreled weapon or other device for testing purposes.


As Hanno indicated:
"The Brinell hardness test was one of the most widely used hardness tests during World War II . For measuring armour plate hardness the test is usually conducted by pressing a tungsten carbide sphere 10mm in diameter into the test surface for 10 seconds with a load of 3,000kg, then measuring the diameter of the resulting depression" (paraphrased)

Reference: CALCE and the University of Maryland, sourced 25 May 2013 from WWW at URL: http://www.calce.umd.edu/TSFA/Hardness_ad_.htm, quoting from http://www.wargamer.org/GvA/background/hardness1.html (does not load)


Posted in response to:
"If you look at the test dimple on the first pic you can make out a small "punch" mark in the middle. That dimple doesn't look like a .303 test hit, too even! On a "hit" you would have some distortion around the outer edge as all rounds don't break up the same on impact."
and:
"The dimple in Michael's picture is nothing like a bullet strike, either AP or Ball. The edges are too defined."

[Mike Cecil]

I believe the testing was done on the plate at the manufacturer, not once the plate was cut up into hull sections, or after it was assembled. The test was specific to ABP3 (Australian Bullet Proof No.3) plate, as this type of plate manufacture/formula was unique to Australia. As far as I can tell from the limited info I've located so far, the testing was done with a test rig and was supposed to simulate a bullet strike by service Ball ammunition, but did not actually use a ball projectile. I've been unable to find any diagrams or descriptions of the test rig, but it was built so the testing was repeatable and consistent, ie was a valid comparative measure of the brittleness and armour qualities of each ABP3 plate. You will find that all the marks - which I agree do not look anywhere like a Ball round impact at 2500-odd fps - are the same and show a flat 'punch' mark, rather than exertion of steady pressure or the impact of a pointed bullet.

ABP3 had a tendency to become very brittle if the final quenching process was done at a slightly varied temperature - early Cruiser tank hulls consistently failed the test because of the difficulties of maintaining the correct temp across such a large structure, whereas flat plate was comparatively easier to control.

ABP3 is unique to Aust armoured vehicles, so I doubt that the exact same rig with a captive pin was used in the UK or elsewhere. Certainly, it appears to be a variation on the standard test method, with pressure, speed of application etc tailored to test the qualities of ABP3, particularly brittleness.

Mike C

[David Dunlop]

Michael.

That test mark you showed was on six locations on one side of my Mk II Cdn Carrier - two, top and bottom rear, centre and front (upper front missing when this piece of plate was cut out. The other side of the carrier had the test marks in the same locations, but each location was a grouping of three marks in the pattern your middle three finger tips would make. The marks were more 'random' on the rest of the carrier - single marks or none at all.

Mike.

You are correct in that these tests were done by the plate manufacturer, prior to delivery to the vehicle maker (at least that is how it worked here in Canada with the plate made for the Carriers built by Ford). The armour plate was time-consuming to make and expensive for the day. It had to be right before going into production. A neighbour of my parents many years ago had been an engineer at the Ford Windsor plant during the war and he told me that when the pattern torch had cut back the side armour at the upper front ends, these small pieces were then used in the fabrication of the armour shrouds surrounding the fan/rad assembly, immediately aft of the front bulkhead. Waste not, want not.

David

[gordon]

Originally Posted by Richard Farrant

The Daimler armoured vehicles made during WW2 had a much more accurate hardness test and done with a very small ball probably only a few millimetres in diameter.

Just another explanatory note here, although the ball used to make the impression was 10mm diameter, the resulting impression could be just 2, 3, or 4 mm on most surfaces, so that would fit quite well.

The surface grinding Richard mentions was to clean up any surface roughness and remove any effects of surface hardening, as the hardness value can drop quite dramatically if you remove as little as 1/32" of metal from the surface.

[David Dunlop]

Rummaged in an album this morning and found a photo of the three cluster hardness test on my old carrier, along with a couple of photos of it 'as found' in a farm yard. The chap had five young grand kids and played in it a lot, but the instruments and mirror were complete and untouched. Used to end great stuff 20 years ago! Harder to do now!

David

[Bob Moseley (RIP)]

Hi all - I have lived with this story for many years. I cannot exactly remember where I heard it but I am sure one source was a WW2 Carrier test driver. However the gauntlet has now been thrown down and the truth needs to be revealed. Watch this space.

Bob

[eddy8men]

i remember during my REME trade training a machine called an izod impact tester. it was basically a weighted pendulum with a ball bearing on the end that hit the test piece with a known amount of force this enabled the material to be rated for hardness by measuring the depth of the indentation. i'm sure carrier armour would have been tested with a machine like that but i'm also sure that most dents you see on a carrier are caused by bullet strikes. my carrier has plenty of dents of varying sizes and 3x 11.5mm holes in the left side panel caused by what i assume to be armour piercing rounds from a boys rifle. if the dents were caused by a measuring machine then the dents would be uniform and all the same depth but if a dent is ragged or oblong it make sense that it was caused by a bullet.
the first pic shows 2 bullet holes on the left panel and the second pic shows the strike marks on the opposite side, the third pic shows a quite large dent but with a flat bottom ? and the last pic shows another penetration hole near the top of the armour that has bent the side with the force of it.

rick