Elastic waves in monoclinic incompressible materials and reflection from an interface

The reflection of plane elastic waves from a free surface of monoclinic incompressible materials is examined under plane strain conditions in a plane of material symmetry. It is found that this problem can be equivalently treated by elastic wave reflection in orthotropic incompressible materials if the material constants of the monoclinic material are properly related to those of the orthotropic material. Thus the range of existence of the two (one homogeneous and the other homogeneous or inhomogeneous) reflected waves in a monoclinic material, including points corresponding to zero amplitude reflected waves, can be obtained from that given in a previous paper [Nair and Sotiropoulos, J. Acoust. Soc. Am. 102, 102–109 (1997)] where an orthotropic material was treated.