LXI. Glancing angle reflection of elastic waves from a free boundary

Abstract

The usual treatment of the reflection of an irrotational wave from a free boundary results for glancing incidence in a seemingly trivial solution where all motion and stress vanishes. In experiment a pressure pulse made to travel at glancing angle along a free boundary trails a shear pulse, but this is properly speaking a diffraction phenomenon, the free boundary beginning at some finite distance. Though this diffraction process cannot be described completely in terms of the reflection treatment, it is possible, by using a limiting process and by changing the interpretation of the variables, to obtain in these terms the asymptotic state far down the free boundary. The result accounts for the trailing shear pulse and is amenable to experimental check.