Callister - An introduction - 8th edition

240 • Chapter 8 / Failure
Grains
SEM Micrograph
Path of crack propagation
Figure 8.6 (a) Schematic crosssection
profile showing crack
propagation through the interior
of grains for transgranular
fracture. (b) Scanning electron
fractograph of ductile cast iron
showing a transgranular fracture
surface. Magnification unknown.
[Figure (b) from V. J. Colangelo
and F. A. Heiser, Analysis of
Metallurgical Failures, 2nd
edition. Copyright © 1987 by
John Wiley & Sons, New York.
Reprinted by permission of John
Wiley & Sons, Inc.]
(a)
(b)
transgranular
fracture
marking patterns will be sufficiently coarse to be discerned with the naked eye. For
very hard and fine-grained metals, there will be no discernible fracture pattern. Brittle
fracture in amorphous materials, such as ceramic glasses, yields a relatively shiny
and smooth surface.
For most brittle crystalline materials, crack propagation corresponds to the
successive and repeated breaking of atomic bonds along specific crystallographic
planes (Figure 8.6a); such a process is termed cleavage. This type of fracture is said
to be transgranular (or transcrystalline), because the fracture cracks pass through