ON RAYLEIGH WAVES AND RAYLEIGH WAVE EXTENSION OF SURFACE MICRO-CRACKS (LAMB SOLUTION, RAYLEIGH SOLUTION, FRACTURE MECHANICS)

The problem under investigation in this dissertation concerns the extension of surface micro-cracks induced by the action of a surface or Rayleigh wave. This problem is examined both theoretically and experimentally. The theoretical approach involves a full-field reappraisal of the original Rayleigh solution for a surface wave propagating in a homogeneous, isotropic, elastic, two-dimensional material, for the cases of plane strain and plane stress. As a refinement to this approach the full-field solution by Lamb is also reconsidered. To obtain a view of the entire field of interest and to compare the Rayleigh and Lamb results, the theoretically predicted isochromatic patterns associated with a propagating Rayleigh wave in two-dimensions are generated. Using the Griffith-Irwin energy release rate fracture criterion for cracks under combined Mode I and Mode II loading, a prediction is made of the path and final length of the surface micro-crack extension produced by the Rayleigh wave. Predictions of the crack extension direction are also obtained using the maximum normal stress fracture criterion. The experimental approach uses dynamic photoelasticity to observe the isochromatic patterns associated with a Rayleigh wave propagating along the narrow edge of a transparent, birefringent plate and also examines in detail the process of crack extension due to a Rayleigh wave. Finally, the theoretically and experimentally obtained results are compared, and reasonable agreement is obtained.