Ultrasonic probe radiation and crack scattering in anisotropic media

摘要

The present project has been concerned with mathematical and numerical modelling of ultrasound in homogeneous anisotropic materials. More specifically, the modelling of ultrasonic probes and crack detection has been in focus. To illustrate the method some examples of grey scale contour plots of the displacement field generated by a probe are given. The most striking difference between an isotropic and an anisotropic material then appears. In an isotropic medium the phase velocity and the group velocity always coincide. In an anisotropic medium they are normally different and even for relatively weak anisotropy the angle between phase and group velocity may be large. In an anisotropic austenitic steel (weld) this angle can be as large as 40 deg. Also a probe on a component with a number of homogeneous anisotropic layers has been investigated. For a layered component comparisons with the simulation program RAYTRAIM have been performed. This is a ray tracing program that follows the group velocity for a number of rays from the probe. To investigate a strip-like interior, near surface or surface-breaking crack an integral equation is employed. For an anisotropic austenitic weld a general comment is that the quasi SV waves behave in a more complicated way than the quasi L and SH waves. As the quasi SV and quasi L waves usually are generated simultaneously it seems that the SH waves should be used if possible. 15 refs, 27 figs.