Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

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2nd Revised Pages

9.5 Principles of Fracture Mechanics • 295

(b)

Grains

SEM micrograph

Path of crack propagation

(a)

Figure 9.6 (a) Schematic

cross-section 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©c1987 by John Wiley

& Sons, New York. Reprinted by

permission of John Wiley & Sons,

Inc.]

cross-sectional area (perpendicular to this load). Due to their ability to amplify an

stress raiser applied stress in their locale, these flaws are sometimes calledstress raisers.

If it is assumed that a crack is similar to an elliptical hole through a plate, and is

oriented perpendicular to the applied stress, the maximum stress,σm, occurs at the

crack tip and may be approximated by

σm= 2 σ 0

(

a

ρt

) 1 / 2

(9.1)

For tensile loading,

computation of

maximum stress at a

crack tip