RAYLEIGH-WAVE INDUCED CRACK EXTENSION

Micro-crack extension induced by both a single and two approaching surface or Rayleigh waves (R-waves) is examined experimentally and theoretically. The experimental model consists of a thin rectangular plate of Homalite 100, a transparent bi-refringent material, on whose edge a micro-crack is located close to where one or two PETN explosive holders are mounted. The events occurring subsequent to setting-off the explosive(s) are photographed using a multiple spark camera equipped to function as a dynamic light field polariscope. This permits the observation of the isochromatic patterns associated with the R-wave(s) and the detailed examination of R-wave induced crack extension. The theoretical model relies on a two-dimensional plane stress description of the propagation of a surface wave in a homogeneous, isotropic, linear elastic material. This full-field description of the R-wave stresses is used in conjunction with a quasi-static Linear Elastic Fracture Mechanics (LEFM) approach to mixed-mode cracking. This approach permits the utilization of the experimental conditions obtained an instant prior to R-wave induced crack extension as input conditions for the theoretical model and allows for the prediction of the crack path and final crack length. A comparison of the experimental and theoretical results yields reasonable agreement. © 1990.