MEASURING RAYLEIGH-WAVES TO INVESTIGATE T HE EROSION AT THE SURFACE OF CRYSTALLINE MATERIALS BY MEANS OF DOUBLE-PULSE HOLOGRAPHIC-INTERFEROMETRY

The repeated impact of solid particles on a material surface results i n erosion. For technical applications as the pneumatic transport the p article diameters are varying between 10(-6) ... 10(-3) m, the mean pa rticle velocities are up to 30 m/s. In order to investigate experiment ally the mechanism of erosion for crystalline materials, planar plates of austenitic steel are damaged due to the repeated impact of spheric al particles. The elastic and plastic deformations, which are produced by this impact, result in propagation of longitudinal and transverse elastic waves into the material and of Rayleigh waves along the materi al surface. The amplitude of the surface deflection due to a single im pacting particle is only 10(-8) ... 10(-7) m. At different states of d amage the surface deflection which is caused by such an impact is meas ured by means of double-pulse holographic interferometry. Because of t he small amplitude of the Rayleigh waves two-reference-beam holographi c interferometry is required. The initial wear of the material is reco gnized by the disturbed propagation of the surface wave.