Interaction of Rayleigh

The phenomenon of friction is one pillar of physics and life would be impossible without it. When two (possibly dissimilar) rough solids are in compressive contact shear stresses can be transmitted through the interface. If the shear stress becomes too large, however, slip will occur and the two bodies move relative to one another into opposite directions. This slip movement can also be achieved in a dynamic situation when surface waves or interface waves propagate along the interface. In this case, the compressive contact will be reduced in a dynamic fashion and a wave-like slip motion will take place. This is associated with a local unloading phenomenon which may lead to global instability of the contact. For material pairings consisting of two dissimilar materials slip movements along the interface (rupture) can occur depending on the fracture and wave speeds. If, therefore, surface (Rayleigh) and interface waves are propagated along a non-ideal contacting interface these waves play a crucial role in the damage and failure of the contacting interfaces. In the general case the dynamic wave and fracture propagation problem is characterized by the four longitudinal and shear wave velocities of the dissimilar materials and the "slip wave" speed. Depending on the speed of slip propagation, subsonic, transonic and supersonic delamination/loss of contact can occur. The most interesting cases seem to be the transonic and supersonic cases where the interface wave speed is higher than at least one of the body wave speeds. In these cases the interface wave runs faster than the body wave and therefore creates a Mach cone front in the acoustically slower material. This Mach front is responsible for large stresses and displacements and, hence, damage which can occur off the interface. Dynamic photoelasticity will be used to identify the wave system which will develop around and within a contact area when a Rayleigh surface wave will interact with a partially contacting interface. It will be shown that a complicated diffraction pattern arises which gives rise to localized dynamic contact slip and damage off the contact region. Numerical simulation using various advanced dynamic codes allow quantitative calculation of the stresses and displacements and quantification of the damage and slip. It will be shown that the Rayleigh/interface wave interaction with contacting interfaces between dissimilar media offers an explanation for some unusual form of damage produced by the recent Kobe earthquake.