GTBL042-09 GTBL042-Callister-v3 October 4, 2007 11:53
2nd Revised Pages322 • Chapter 9 / FailureRegion of slow
crack propagationRegion of rapid failureFigure 9.30 Fatigue
failure surface. A crack
formed at the top edge.
The smooth region also
near the top corresponds
to the area over which the
crack propagated slowly.
Rapid failure occurred
over the area having a
dull and fibrous texture
(the largest area).
Approximately 0.5×.
[Reproduced by
permission fromMetals
Handbook: Fractography
and Atlas of Fractographs,
Vol. 9, 8th edition, H. E.
Boyer (Editor), American
Society for Metals, 1974.]Often the cause of failure may be deduced after examination of the failure sur-
faces. The presence of beachmarks and/or striations on a fracture surface confirms
that the cause of failure was fatigue. Nevertheless, the absence of either or both does
not exclude fatigue as the cause of failure.
One final comment regarding fatigue failure surfaces: Beachmarks and striations
will not appear on that region over which the rapid failure occurs. Rather, the rapid
failure may be either ductile or brittle; evidence of plastic deformation will be present
for ductile, and absent for brittle, failure. This region of failure may be noted in Figure
9.30.Concept Check 9.4
Surfaces for some steel specimens that have failed by fatigue have a bright crystalline
or grainy appearance. Laymen may explain the failure by saying that the metal
crystallized while in service. Offer a criticism for this explanation.[The answer may be found at http://www.wiley.com/college/callister (Student Companion Site).]9.13 FACTORS THAT AFFECT FATIGUE LIFE^9
As mentioned in Section 9.10, the fatigue behavior of engineering materials is highly
sensitive to a number of variables. Some of these factors include mean stress level,(^9) The case study on the automobile valve spring found in Sections M.7 through M.9 of Web
Module M relates to the discussion of this section.