METHODS OF SAMPLING AND TESTING HIGHWAY MATERIALS 127 
testsi the relation between applied load,* P, measured in kilograms, and 
diameter of ball, D. measured in millimeters, should be 
D 2 
P =3,000 yj^ =30 TV for iron and steel 
7)2 
and P= 500 ~ = 5D 2 for brass, bronze, and soft metals in general. 
For extremely soft metals the relation P=D 2 may be used. 
Balls differing in size from the standard 10-millimeter ball shall conform to 
the requirements for the material and the tolerance in size of diameter as 
specified for the standard ball. 
TEST SPECIMENS 
Specimens used in Brinell hardness testing vary greatly in form since it is 
frequently desirable to make the impression upon a part to be used in the 
finished product rather than upon a sample test specimen. 
4. The thickness of the piece tested shall be such that no bulge or other 
marking showing the effect of the load appears on the side of the piece 
opposite the impression. In any event, the thickness of the specimen shall be at 
least ten times the depth of impression. 
5. The surface on which the impression is to be made shall be filed, ground, 
machined, or polished with emery paper so that the edge of the impression 
shall be clearly enough defined to permit of the measurement of the diameter 
within 0.01 millimeter (0.0004 inches). 
APPLICATION AND MAGNITUDE OF LOAD 
6. The load in the standard Brinell test shall be 3,000 kilograms for iron 
and steel and 500 kilograms for brass, bronze, and soft metals generally. 
Note. — For extremely soft metals a load of 100 kilograms is sometimes used. If for 
any reason it is necessary to use loads differing from those specified above, the load used 
should be specifically stated in the test report, conveniently as a subscript of the hardness 
numeral. 
7. (a) The load shall be applied steadily to the specimen without jerk. 
(&) The load shall be applied for at least 10 seconds in the case of iron 
and steel and for at least 30 seconds in the case of other metals. 67 
(c) The center line of the applied load shall be far enough from any edge 
of the specimen so that when a straightedge is applied to the edge after the 
load has been applied, the eye can detect no bulge in the edge due to the load 
and the resulting impression. 
MEASUREMENT OF IMPRESSION 
8. In the standard Brinell hardness test the diameter of the impression shall 
be measured. 
9. When a micrometer microscope is used to measure the diameter of the 
impression the sharpness of definition of the edge of the impression can be in- 
creased by the use of a movable lamp for illuminating the specimen, placing 
the lamp so that the contrast of light and shade will bring first one edge of 
the impression, then the other into sharp definition. In testing very hard ma- 
terial, the sharpness of definition of the impression can be somewhat increased 
by the use of a ball lightly etched with nitric acid, or by the use of some pig- 
ment, such as Prussian blue, on the ball. In testing material in which there 
is considerable recovery of shape, the material may first be coated with a 
dull black pigment, such as drawing ink or a mixture of graphite and alcohol. 
The edge of the impression is rendered clear on a surface so coated. 
BRINELL HARDNESS TESTS IN WHICH DEPTH OF IMPRESSION IS 
MEASURED IN PLACE OF DIAMETER 
When it is necessary to make Brinell hardness tests very rapidly, as is some- 
times the case when the Brinell test is used as a control test for the output 
67 It was suggested in discussion that for magnesium and magnesium alloys the 
minimum time of application be two minutes. It was also suggested that for any given 
soft metal a definite time for holding the load be specified rather than a minimum time. 
See discussion of the report of committee E-l. (16, p. 729-730). 
