Is this a shot test

[Nathan Clark]

I agree with Bob on this one, I believe that the test holes were done with a firearm, most likely with a 303 as Bob suggested. My proof to this theory is the fact that all test holes done on 1824 in particular still have trace elements of lead in the test holes and they are not all unison in size or shape. If they were done with a punch or a rivet gun etc. all the holes would be perfect and unison in shape. I know for a fact that the holes were put in 1824 before construction and are not battle or post-war related because they are mostly in spots that would be impossible to shoot or 'test' once the carrier was assembled. The steel in a LP2a would have been designed to stop rounds up to .303 in calibre so if you were going to test the steel during construction, if would have been quite simple to just discharge a .303 at it and find out wouldn't it?

Nathan

[Michael R.]

Well, I suppose if you expected your carrier to be fired upon by the standard .303BRIT round, it may be reasonable to perform a proof test to that standard. A .303BRIT standard bullet would have a jacket made of a material that encases a lead core. Could one expect the adversary to be equipped and shooting at you with 7.92x57 or perhaps 7.7x58 ? Those rounds would likely be fired from a distance and angle other than what we see in the LP2A. Close range and at right angles would be a worse case scenario. Not to mention 20mm Solothurn ... Quite interesting Nathan. I do not doubt the possibility that a rifle round may have created the mark shown: I am simply intrigued that it enters production.

Why would a factory invest time and material to produce an armoured vehicle without having knowledge ahead of time that the material meets standard?

It is a common practice to test assorted armour under simulated field conditions on post production items, in particular at set periods of time during service life. Once the armour has been struck by a round, it is not deemed appropriate to return the item to stock for service issue.


Here is an image showing an example of a heat treated Canadian Universal Carrier side plate, displaying what I believe is the hardness test dimple,(update, not from a bullet strike) along with strike marks left from the straightening process, and the control or registration number of the production plate. The number is not related to the lower hull number, upper hull number, serial number or WD number. On the sample shown, the opposite side plate of the Carrier has a non-sequential number.


There are numerous wartime examples showing Canadian Universal Carrier armour was defeated by enemy small arms fire. Here is an image of a captured Canadian made MKI* that has gone through the retrofit program to the MKII UCW standard. You can see the side plate has been struck at an acute angle and defeated. June, 1944, France. Ignore the red circles, they identify the deep wading plate pads over the MKI* folding armour.

As a side note, you can see this Carrier being driven by the adversary, as it is brought along side of a Sherman. See minute 7:49 in: http://www.youtube.com/watch?v=Dpb9_YS3CzE

[Hanno Spoelstra]

Originally Posted by Michael R.

It is a common practice to test assorted armour under simulated field conditions on post production items, in particular at set periods of time during service life. Once the armour has been struck by a round, it is not deemed appropriate to return the item to stock for service issue.

Here is an image showing an example of a heat treated Canadian Universal Carrier side plate, displaying what I believe is the hardness test dimple, along with strike marks left from the straightening process, and the control or registration number of the production plate. The number is not related to the lower hull number, upper hull number, serial number or WD number. On the sample shown, the opposite side plate of the Carrier has a non-sequential number.

I agree, the dimple is a sign of the hardness testing method, most likely the Brinell Hardness Test:

Brinell hardness is determined by forcing a hard steel or carbide sphere of a specified diameter under a specified load into the surface of a material and measuring the diameter of the indentation left after the test.The Brinell hardness number, or simply the Brinell number, is obtained by dividing the load used, in kilograms, by the actual surface area of the indentation, in square millimeters.The result is a pressure measurement, but the units are rarely stated.
(...)
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.

The number most likely is the lot or batch number of the batch of plates going through the hardening process at the same time. Typically only a few samples of a batch are tested, and if the samples fail the test the whole batch is rejected or reworked. The batch number is used to ID the plates that need to be rejected or reworked.

Testing each plate by firing a bullet sounds like a laborious, dangerous, costly process with unreliable results as there is too much variation. To rule out variation in hardness testing, men like Brinell, Rockwell and Vickers developed standardized tests with reliable measured outcomes.

For what's my €0,02 worth, anyway.
Hanno

[Paul Dutton]

Originally Posted by Michael R.

Well, I suppose if you expected your carrier to be fired upon by the standard .303BRIT round, it may be reasonable to perform a proof test to that standard. A .303BRIT standard bullet would have a jacket made of a material that encases a lead core. Could one expect the adversary to be equipped and shooting at you with 7.92x57 or perhaps 7.7x58 ? Those rounds would likely be fired from a distance and angle other than what we see in the LP2A. Close range and at right angles would be a worse case scenario. Not to mention 20mm Solothurn ... Quite interesting Nathan. I do not doubt the possibility that a rifle round may have created the mark shown: I am simply intrigued that it enters production.

Why would a factory invest time and material to produce an armoured vehicle without having knowledge ahead of time that the material meets standard?

It is a common practice to test assorted armour under simulated field conditions on post production items, in particular at set periods of time during service life. Once the armour has been struck by a round, it is not deemed appropriate to return the item to stock for service issue.


Here is an image showing an example of a heat treated Canadian Universal Carrier side plate, displaying what I believe is the hardness test dimple, along with strike marks left from the straightening process, and the control or registration number of the production plate. The number is not related to the lower hull number, upper hull number, serial number or WD number. On the sample shown, the opposite side plate of the Carrier has a non-sequential number.


There are numerous wartime examples showing Canadian Universal Carrier armour was defeated by enemy small arms fire. Here is an image of a captured Canadian made MKI* that has gone through the retrofit program to the MKII UCW standard. You can see the side plate has been struck at an acute angle and defeated. June, 1944, France. Ignore the red circles, they identify the deep wading plate pads over the MKI* folding armour.

As a side note, you can see this Carrier being driven by the adversary, as it is brought along side of a Sherman. See minute 7:49 in: http://www.youtube.com/watch?v=Dpb9_YS3CzE

If you look at the test dimple on the first pic you can make out a small "punch" mark in the middle. That dimple doesnt look like a .303 test hit, too even! On a "hit" you would have some distortion around the outer edge as all rounds dont break up the same on impact. Thats my Tuppence (Nickles...!!!) worth.

[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]

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."

[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.