Callister - An introduction - 8th edition

8.6 Fracture Toughness Testing • 253
Figure 8.13
Temperature
dependence of the
Charpy V-notch
impact energy (curve
A) and percent shear
fracture (curve B)
for an A283 steel.
(Reprinted from
Welding Journal.
Used by permission
of the American
Welding Society.)
Impact energy (J)
100
80
60
40
Temperature (°F)
–40 0 40 80 120 160 200 240 280
Impact
energy
B
A
Shear
fracture
100
80
60
Shear fracture (%)
40
20
20
0
–40 –20 0 20 40 60 80 100 120 140
0
Temperature (°C)
fracture appearance (e.g., 50% fibrous fracture). Matters are further complicated
inasmuch as a different transition temperature may be realized for each of these criteria.
Perhaps the most conservative transition temperature is that at which the fracture
surface becomes 100% fibrous; on this basis, the transition temperature is
approximately 110C (230F) for the steel alloy that is the subject of Figure 8.13.
Structures constructed from alloys that exhibit this ductile-to-brittle behavior
should be used only at temperatures above the transition temperature, to avoid brittle
and catastrophic failure. Classic examples of this type of failure occurred, with
disastrous consequences, during World War II when a number of welded transport
ships, away from combat, suddenly and precipitously split in half. The vessels were
constructed of a steel alloy that possessed adequate toughness according to roomtemperature
tensile tests. The brittle fractures occurred at relatively low ambient
temperatures, at about 4C (40F), in the vicinity of the transition temperature
of the alloy. Each fracture crack originated at some point of stress concentration,
probably a sharp corner or fabrication defect, and then propagated around the entire
girth of the ship.
59 12 4 16 24 79
Figure 8.14 Photograph of fracture surfaces of A36 steel Charpy V-notch specimens
tested at indicated temperatures (in C). (From R. W. Hertzberg, Deformation and Fracture
Mechanics of Engineering Materials, 3rd edition, Fig. 9.6, p. 329. Copyright © 1989 by John
Wiley & Sons, Inc., New York. Reprinted by permission of John Wiley & Sons, Inc.)