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Hardness tests on impact test specimens |
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|  MIL-A-12560H (MR)
w/INT. AMENDMENT 4
4.6.2.1 Hardness tests on impact test specimens. Samples for all classifications shall be examined
on a lot by lot basis. Except as provided in 4.6.2.2, each sample from which impact test
specimens are taken shall have a hardness check made upon it as follows: For samples 1/4 to 1/2
inch inclusive the hardness check shall be made on the surface. For samples of 1/2 inch up to 4
inches in thickness, at least two hardness tests shall be taken from an adjacent location, midway
between the surfaces of the plate. For samples of 4 inches in thickness or greater, at least six
hardness tests shall be made at equal intervals across the plate thickness.
4.6.2.2 Rockwell hardness tests on impact specimens. At the option of the contractor at least two
Rockwell C hardness tests shall be made on each impact test specimen sampled from each lot.
The test specimens shall be prepared and tested in accordance with ASTM E18. The average
shall not exceed the maximum requirement for thickness specified in table II.
4.6.3 Charpy V-notch impact tests. At least two Charpy V-notch impact test specimens shall be
taken in each direction from each sample as obtained in accordance with 4.6.3.1 or 4.6.3.2, and
shall be prepared and tested in accordance with ASTM E23.
4.6.3.1 For samples less than 4 inches in thickness. Charpy V-notch impact test specimens from
samples less than 4 inches in thickness shall be taken in both the TL orientation and in the LT
(see 3.2.5.2) orientation from a location midway between the top and bottom surfaces of the plate
and at least 4 inches or 2T, whichever is less, from any quenched edge as well as outside the heat
affected zone of any thermal-cut edge. When the amount of materials available is insufficient to
obtain standard specimens, the largest attainable subsize Charpy V-notch impact specimens
shown in figure 3 of ASTM E23 shall be used and the results compared to the applicable
requirements of table VI.
4.6.3.2 For sample 4 inches or greater in thickness. Charpy V-notch impact test specimens from
samples 4 inches or greater in thickness shall be approximately 1 inch below the surface of the
plate and at least 4 inches from any quenched edge as well as outside the heat-affected zone of
any thermally-cut edge.
4.6.4 Ballistic tests. Ballistic testing of armor plate shall be conducted at a Government test
facility specified in the contract or order or at a test facility approved by the Government.
Testing shall be conducted in accordance with the requirements of the appendix.
4.6.5 Ultrasonic examination.
4.6.5.1 Inspection equipment. The ultrasonic soundness inspection equipment shall conform to
ASTM A578/A578M.
4.6.5.2 Procedure. Unless otherwise specified (see 6.2), the ultrasonic examination shall be
carried out in accordance with ASTM A578/A578M with the following exceptions.
(a)
Scanning shall be continuous over 100% of the plate surface.
(b)
Scanning rate shall be at a speed where recordable discontinuities can be detected.
(c)
The testing frequency shall be a minimum of 2 megahertz (MHz).
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