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