The Stress-Wave Radiation from Growing Cracks.

Explicit formulae are given for the stress discontinuities radiated by a suddenly starting two-dimensional crack under tension, in an ideal elastic body. These formulae also give, with a change in sign, the stress discontinuities radiated by a suddenly stopping crack, and, with a geometrical deformation, those radiated by a three-dimensional crack. The stress in the primary radiation due to short crack-jumps is thus shown to vary in essentially the same manner as does the crack speed during the jump. The diffraction of the primary radiation from one tip of a centre-crack by the other tip produces a secondary radiation, whose properties depend mainly on the nature of the surface wave associated with the primary radiation. Since this first diffraction can lead to crack extension, further diffractions would be difficult to study analytically. If it is possible to isolate the primary radiation experimentally, however, it should give directly the essential characteristics of the source. This could be used to separate source-characteristics from specimen and transducer effects in acoustic emission studies of fatigue cracking, or stress-corrosion cracking. Author