GTBL042-09 GTBL042-Callister-v3 October 4, 2007 11:53
2nd Revised Pages294 • Chapter 9 / Failure(a)(b)
Figure 9.5 (a) Photograph showing V-shaped “chevron” markings characteristic of brittle
fracture. Arrows indicate origin of crack. Approximately actual size. (b) Photograph of a
brittle fracture surface showing radial fan-shaped ridges. Arrow indicates origin of crack.
Approximately 2×.[(a) From R. W. Hertzberg,Deformation and Fracture Mechanics of
Engineering Materials,3rd edition. Copyright©c1989 by John Wiley & Sons, New York.
Reprinted by permission of John Wiley & Sons, Inc. Photograph courtesy of Roger Slutter,
Lehigh University. (b) Reproduced with permission from D. J. Wulpi,Understanding How
Components Fail,American Society for Metals, Materials Park, OH, 1985.]discrepancy is explained by the presence of very small, microscopic flaws or cracks
that always exist under normal conditions at the surface and within the interior of
a body of material. These flaws are a detriment to the fracture strength because
an applied stress may be amplified or concentrated at the tip, the magnitude of
this amplification depending on crack orientation and geometry. This phenomenon
is demonstrated in Figure 9.8, a stress profile across a cross section containing an
internal crack. As indicated by this profile, the magnitude of this localized stress
diminishes with distance away from the crack tip. At positions far removed, the
stress is just the nominal stressσ 0 , or the applied load divided by the specimen