Radiation from a tensile fracture

The radiation pattern for elastic waves from a tensile fracture has been observed in a two-dimensional model. The fracture is induced by a local concentration of thermal stresses. The observed radiation pattern for the first motions is compared with that predicted by two different theoretical calculations, one by Ang and Williams and the other by Knopoff and Gilbert. The experiment does not reproduce all of the conditions of either theory, but arguments are advanced which suggest that the theoretical predictions are applicable to the observations. Although there is generally a qualitative agreement between experiment and theory, the quantitative agreement is poor. The principal criticism of the experiment is that the first motions are emergent, and the experimentally measured amplitudes may not characterize the true first motion. On the other hand, linear elasticity is assumed in both theories. Inasmuch as fracture involves nonlinear processes, it may be that the theories cannot properly be applied to radiation from a fracture.