Page 297 - Mechanical Engineer's Data Handbook

ENGINEERING MEASUREMENTS 285

Toothed wheel and
eleCIriCBl pick-up

and indiitor

7.9 Materials-testing measurements

7.9. I Hardness testing Let :
D =diameter of indentation (mm j
Hardness tests on materials consist of pressing a D, = diameter of ball (mm)
hardened ball or point into a specimen and measuring F=force on ball (kg)
the size of the resulting indentation. The two methods
shown are the Brinell method, which utilizes a ball, Values of F: steel, F=300<; copper, F= 1OD<; alu-
and the Vicker's pyramid method which utilizes a minium, F = 5 0:
pyramidal point. Hardness BHN = F
Other methods in use are the Rockwell method 1 .57D,(D,- dm)
which uses a ball or diamond cone, and the Shore
scleroscope, a portable instrument which measures the Vicker's pyramid number (VPN)
height of rebound of a hammer falling on the surface.
Let:
Measurement of Brinnel hardness number F=load (kg)
(BHN) b = diagonal of indentation (mm)
F
The ball size is 10 mm for most cases or 1 mm for light VPN = 1.854 -
bZ
work.

I'