Page 296 - Materials Science and Engineering An Introduction

268 • Chapter 8 / Failure

Figure 8.13 Temperature Temperature (°F)
dependence of the Charpy V-
notch impact energy (curve A) and –40 0 40 80 120 160 200 240 280
percent shear fracture (curve B) for
an A283 steel. 100
(Reprinted from Welding Journal. Used
by permission of the American Welding A
Society.)
80
100
Impact energy (J) 60 energy fracture 80 Shear fracture (%)
Impact
Shear

Tutorial Video: 40 B 60
Ductile-to-Brittle 40
Transition Failure
How do I Interpret 20
the Ductile-to-Brittle 20
Transition Failure
Graphs and Equations?
0 0
–40 –20 0 20 40 60 80 100 120 140
Temperature (°C)

Alternatively, appearance of the failure surface is indicative of the nature of frac-
ture and may be used in transition temperature determinations. For ductile fracture,
this surface appears fibrous or dull (or of shear character), as in the steel specimen of
Figure 8.14, which was tested at 79 C. Conversely, totally brittle surfaces have a granular
(shiny) texture (or cleavage character) (the 59 C specimen in Figure 8.14). Over the
ductile-to-brittle transition, features of both types will exist (in Figure 8.14, displayed by
specimens tested at 12 C, 4 C, 16 C, and 24 C). 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 the temperature at which the CVN energy assumes
some value (e.g., 20 J or 15 ft-lb f ), or corresponding to some given fracture appearance
(e.g., 50% fibrous fracture). Matters are further complicated by the fact that 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 110 C (230 F) for the
steel alloy that is the subject of Figure 8.13.

Figure 8.14 Photograph of fracture 59 12 4 16 24 79
surfaces of A36 steel Charpy V-notch
specimens tested at indicated tempera-
tures (in C).
(From R. W. Hertzberg, Deformation and
Fracture Mechanics of Engineering Materi-
als, 3rd edition, Fig. 9.6, p. 329. Copyright
© 1989 by John Wiley & Sons, Inc., New
York. Reprinted by permission of John
Wiley & Sons, Inc.)