Identification of aircraft by Rockwell test

Horace Knerr
naca-tn-342
Jun 1930


A large number of tests were made on tubes of 1025 and 4130X steel, in various diameters and wall thicknesses, and after diverse heat treatments. The Rockwell B scale was employed, as being the best suited to the ranges of hardness encountered. Only satisfactory chrome molybdenum tubes were found to show a hardness in excess of 90-B after normalizing. The method therefore provided the desired means of identification of chrome molybdenum steel. It is a qualitative test only. The conditions of a satisfactory test are as follows. 1) The tubing must be normalized. 2) It must be clean inside and out at the point where the test is to be made. 3) The tube must be held in correct alignment with the penetrator and must not move during the test. 4) For thin-walled tubes, the anvil must extend within the tube so as to support the wall.

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http://naca.central.cranfield.ac.uk/reports/1930/naca-tn-342.pdf