Materials for engineering, 3rd Edition - (Malestrom)

Determination of mechanical properties 47
Brinell
800
700
600
500
400
Shore A
Vickers (H v )
Rockwell C
300
200
100
0
Rockwell B
200 400 600 800 1000
30 40 50 60 70 80 90 100 110 120Shore A
H V
60 70 80 90 100
20 30 40 50 60 70
2.8 Relation between various scales of hardness.
Rock. B
Rock. C
172.5°, thus giving a rhombohedral impression with one diagonal (L) being
7 × longer than the other and with a depth which is one thirtieth of L. It is
particularly useful for measuring the relative hardnesses of brittle materials,
such as glasses and ceramics, when lower loads (P) are employed than in the
Vickers test.
The Knoop Hardness Number (KHN, in kgf mm –2 ) is given by the relation:
KHN = 14.229P/L 2
2.5.6 The Shore scleroscope
A small diamond-pointed hammer weighing 2.5 g falls freely from a standard
height down a graduated glass tube. The height of the first rebound is taken
as the index of hardness and this simple apparatus may be readily transported
for testing rolls, gears, etc. in situ. Its correlations with the indentation hardness
techniques are also shown in Fig. 2.8.
The Shore test may also be employed to measure the elastic response of
elastomers, as a check of the degree of cross-linking.
2.6 Fracture toughness testing
The toughness of a material must be distinguished from its ductility. It is true
that ductile materials are frequently tough, but toughness combines both
strength and ductility, so that some soft metals like lead are too weak to be