Callister - An introduction - 8th edition

252 • Chapter 8 / Failure
Figure 8.12
(a) Specimen used
for Charpy and Izod
impact tests. (b) A
schematic drawing of
an impact testing
apparatus. The
hammer is released
from fixed height h
and strikes the
specimen; the energy
expended in fracture
is reflected in the
difference between h
and the swing height
h. Specimen
placements for both
Charpy and Izod
tests are also shown.
[Figure (b) adapted
from H. W. Hayden,
W. G. Moffatt, and
J. Wulff, The Structure
and Properties of
Materials, Vol. III,
Mechanical
Behavior, p. 13.
Copyright © 1965 by
John Wiley & Sons,
New York.
Reprinted by
permission of John
Wiley & Sons, Inc.]
Izod
Notch
10 mm
(0.39 in.)
Pointer
10 mm
(0.39 in.)
Scale
Charpy
(a)
Starting position
Hammer
8 mm
(0.32 in.)
End of swing
Specimen
h
h'
Anvil
(b)
Over the ductile-to-brittle transition, features of both types will exist (in Figure 8.14,
displayed by specimens tested at 12C, 4C, 16C, and 24C). Frequently, the percent
shear fracture is plotted as a function of temperature—curve B in Figure 8.13.
For many alloys there is a range of temperatures over which the ductile-to-brittle
transition occurs (Figure 8.13); this presents some difficulty in specifying a single
ductile-to-brittle transition temperature. No explicit criterion has been established,
and so this temperature is often defined as that temperature at which the CVN
energy assumes some value (e.g., 20 J or 15 ft-lb f ), or corresponding to some given