SCATTERING BY 2 PENNY-SHAPED CRACKS WITH SPRING BOUNDARY-CONDITIONS

The elastodynamic scattering by a penny-shaped crack with spring bound ary conditions is investigated. The transition (T) matrix of the crack is determined and the usefulness of this is illustrated by considerin g also the scattering by two cracks. The T matrix of a single crack is first determined by a direct integral equation method which gives the crack-opening displacement and the integral representation which subs equently gives the scattered field expanded in spherical waves. Two cr acks are considered by a multi-centred T matrix approach where matrix inverses are expanded in Neumann series. Rotation matrices are employe d so that the cracks may have an arbitrary orientation. The back-scatt ered longitudinal far field amplitude is computed both in the frequenc y and time domain in a few cases and the effects due to multiple scatt ering are in particular explored.