Page 166 - Failure Analysis Case Studies II

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15

0 0.2 0.4 0.6 0.8 1
COD (mm)

5 c"

0 0.1 0.2 0.3 0.4 0.5
COD (mm)
Fig. 4. Load vs crack opening displacement records. (a) Notched beams. @) Short bars.

elliptical cracks, as sketched in Fig. 5 (a and b are the ellipse semi-axes). The stress intensity factor
for this geometry was numerically computed in 1976 by Astiz [4, 51 and also by photoelastic
techniques by the authors [6]. When b > a the maximum stress intensity factor is at point A (see
Fig. 5) and its value can be expressed as

where P is the applied load and D is the bar diameter. The coefficients C, are given in Table 4. A

Table 4. Values of C,
cu j=O 1 2 3
i=O 1.118 -0.179 -0.339 0.130
i=2 1.405 5.902 -9.057 3.032
i=3 3.891 -20.370 23.217 -7.555
i=4 8.328 21.895 - 36.992 12.676