124 DEPARTMENT BULLETIN 1216, U. S. DEPT. OF AGRICULTURE 
14. (a) The term "yield point" in compression is defined the same as in 
tension, as follows : 
Yield point. — The stress in a material at which there occurs a marked increase 
in strain without an increase in stress. 
(&) The same methods for determining yield point as given in section 21 of 
the tentative methods of tension testing of metallic materials (serial designation, 
E 8-27 T, see p. Ill) shall he used. The method by the use of dividers or by 
the use of a strainometer seems generally suitable for compression testing. 
15. The term " compressive strength " is defined as follows : 
Compressive strength. — The maximum compressive stress which a material is 
capable of developing. 
Note. — In the case of a material which fails in compression by a shattering fracture 
the compressive strength has a very definite value. In the cast' of materials which do 
not fail in compression by a shattering fracture the value obtained for compressive 
.strength is an arbitrary value, depending upon the degree of distortion which is regarded 
as indicating complete failure of the metal. 
PLOTTING STRESS-STRAIN DIAGRAMS 
16. The discussion and directions given in section 25 of the tentative methods 
of tension testing of metallic materials (serial designation. E 8-27 T, see p. 
Ill (5) apply to plotting stress-strain diagrams for compression tests. 
70. STANDARD METHODS OF BRINELL HARDNESS 
TESTING OF METALLIC MATERIALS 64 
(A. S. T. M. standard method (S) serial designation E 10-27) 
The Brinell test for determining the hardness of metallic materials consists 
in applying a known load to the surface of the material to be tested through a 
hardened steel ball of known diameter. The diameter (or depth) of the result- 
ing permanent impression in the metal is measured. The Brinell hardness 
number is taken as the quotient of the applied load divided by the area of the 
surface of the impression, which is assumed to be spherical. If P is the applied 
load (measured in kilograms), D is the diameter of the steel ball (measured in 
millimeters) and d is the diameter of the impression (measured in millimeters), 
then : 
p 
B.H.X 
ivDfD— JD 2 — d^ 
2 
rv 
in which B.H.N, is the Brinell hardness number in kilograms per square 
millimeter. 
It' the steel ball were not deformed under the applied load and if the impres- 
sion were truly spherical, then the above formula would be a general one, 
and any combination of applied load and size of ball could be used. As the 
impression is not quite a spherical surface (since there must always be some 
deformation of the steel ball and some recovery of form of the metal in the 
impression), for a standard Brinell test the size and characteristics of the ball 
and the magnitude <>f the applied load must be standardized. (A standard ball 
10 millimeters in diameter and a load of 3.000 kilograms for hard metals and 
500 kilograms for soft metals is standard practice. See sections 3 and 6.) 
In Table 12 is given the Brinell hardness number corresponding to various 
diameters of impression for both 500 and 3.000-kilogram load, making it unneces- 
sary to compute for each test the value of the Brinell hardness number by the 
above formula. 
14 Under the standardization porcedure of the society, these methods are under the 
jurisdiction of the A. S. T. M. committee E-l on methods of testing. These methods are 
in effect a revision of the methods for Brinell hardness tests of the standard methods of 
mechanical testing of metallic materials. The standard methods, which were last pub- 
lished under the serial designation E 1-18, have accordingly been withdrawn. 
