Page 207 - T. Anderson-Fracture Mechanics - Fundamentals and Applns.-CRC (2005)

1656_C004.fm Page 187 Thursday, April 21, 2005 5:38 PM

Dynamic and Time-Dependent Fracture 187

FIGURE 4.13 Crack arrest experiments on wedge-loaded DCB Araldite B specimens. The statically inter-
preted arrest toughness underestimates the true K IA of the material; this effect is most pronounced for long
crack jumps. Taken from Kalthoff, J.F., Beinart, J., and Winkler, S., “Measurement of Dynamic Stress Intensity
Factors for Fast Running and Arresting Cracks in Double-Cantilever Beam Specimens.” ASTM STP 627,
American Society for Testing and Materials, Philadelphia, PA, 1977, pp. 161–176.

Recall the schematic in Figure 4.8, where it was argued that arrest, when quantified by the
quasistatic stress intensity, would occur below the true arrest toughness K , because of the kinetic
IA
energy in the specimen. This argument is a slight oversimplification, but it leads to the correct qualitative
conclusion.
The DCB specimen provides an extreme example of reflected stress wave effects; the specimen
design is such that stress waves can traverse the width of the specimen and return to the crack tip
in a very short time. In many structures, the quasistatic approach is approximately valid, even for
relatively long crack jumps. In any case, K gives a lower bound estimate of K , and thus is conservative
IA
Ia
in most instances.