Page 334 - T. Anderson-Fracture Mechanics - Fundamentals and Applns.-CRC (2005)

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314 Fracture Mechanics: Fundamentals and Applications

FIGURE 7.16 Effect of ligament length on apparent fracture toughness in an aluminum alloy. Taken from
Kaufman, J.G. and Nelson, F.G., ‘‘More on Specimen Size Effects in Fracture Toughness Testing.’’ ASTM STP
559, American Society for Testing and Materials, Philadelphia, PA, 1973, pp. 74–98. Wallin, K., ‘‘Critical Assess-
ment of the Standard E 399.’’ ASTM STP 1461, American Society for Testing and Materials, Philadelphia, PA, 2004.

where A and m are material constants. Using the above expression, and assuming that nonlinearity
in the load-displacement curve is due entirely to crack growth, it is possible to compute the P /P
max Q
ratio for standard test specimens. Figure 7.18 shows the results of such an exercise for the compact
specimen [13]. The load ratio is a function of the exponent m, but is insensitive to a/W. Moreover,
this analysis predicts that the computed P /P ratio is completely independent of the absolute
max Q

FIGURE 7.17 Schematic illustration of the inherent size effect in K Q , as it is defined by the ASTM E 399
test method.