Is this a shot test

[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

[Ian Patrick]

The front armour plate on my LP2A carrier and some other LP2/2A carriers I've seen have test marks that appear to have been caused by a bullet-like impact.

These appear to be reasonably consistently located in the same spot(s) on various different carriers which would seem to indicate that the test was undertaken either after the carrier was assembled or at least when the front armour plate had been cut to shape. Logically this would indicate the testing was done at the carrier assembly plant rather than the steel manufacturing plant.

These marks have not been caused by a ball striking the plate but appear to be from a small diameter sharp object hitting the plate with some force.

Any ideas?

Ian

[Ian Patrick]

Another test mark from a different carrier, SA Railways LP2A 2515.

[45jim]

Gentlemen,

No armour plate destined to be assembled onto or into a vehicle is proofed by actual ballistic testing. Any marks you see on your carriers either are a result of mechanical testing of the hardness using conventional test methods at the steel works or a result of "life experience" during the past 70 years.

Armour plate is produced just like any other blend of steel. It is composed of a carefully balanced mix of iron, carbon and other additives smelted into ingots. Later, those ingots are either cold or hot rolled into plate which is further heat treated to achieve the hardness and mechanical properties set down in the relevant specification. The standards, methodology and instruments used to confirm the hardness of armour plate are the same used for any production run of steel.

Armour plate production today is not much different. Plates are manufactured and heat treated in "heats" and a sample of the "heat" is tested to ensure the hardness meets the standard and metallurgy is scientifically examined, also a sample is sent to a ballistic test range to verify its performance. As the volume of successful testing increases the amount of testing will be reduced. Early in production every lot may be tested but later it may be every two or every three, depends on the demand of the customer.

Ballistic testing is "destructive testing" while hardness testing (in steel anyway) is considered "non-destructive testing" so there is no way that shot plates are going to end up on a carrier. As you can imagine with any scientifically designed standard, hardness is calculated as "averages" so many impacts may be taken on a single surface to get an accurate reading. Ballistic testing is the same, we often fire 10 rounds (or more) at a target at various velocities to ensure we have an accurate value of the Ballistic Limit (BL).

If you are curious, you can look up MIL-A-46100, this is the NATO specification for 500BHN armour plate steel. It details everything including the type of testing required and the ballistic limits samples must achieve. You will notice that the plate is tested for Brinell hardness, Impact testing (Charpy V-notch), bending test and finally ballistic sample testing. This is not a classified standard.

There are certainly other blends such as RHA (rolled Homogeneous armour) which is somewhat softer and more ductile than 46100, but this standard originated in WWII and closely reflects what was used on the carrier.