The Velocity of Dilatation and Rayleigh Waves in Metal Bars

Abstract

Single elastic waves in rock and metal specimens were studied by partially immersing the specimen in water and observing the body waves in the water by means of spark shadowgrams. The waves were started by impact from a fast moving steel sphere. Waves in the water were observed to come from the dilatation body wave and the Rayleigh surface-wave in the solid. Using the slope of the wave front in water, the dilatation wave velocities were measured for cold-rolled steel, yellow brass, and an aluminum alloy, as well as for two rock specimens, a marble and a diabase. These agreed well with the velocities calculated from the elastic constants. The velocity of the first wave or pulse was found to correspond to the velocity of a dilatation wave in an infinite medium, while the wave velocities which were measured when the bar was in resonant oscillation were observed to have values characteristic of a dilatation wave in a narrow bar. The Rayleigh surface wave velocities were measured in steel, brass, and an aluminum alloy and showed good agreement with the theory. None of the surface waves was strong enough in the rock specimens to be observed. Spark shadowgrams were also made, showing that a Rayleigh wave is produced when a dilatation wave passes through an interface at nearly normal incidence. Rayleigh waves were also observed to produce a second Rayleigh wave at a square corner, demonstrating that the Rayleigh wave has a component of displacements which is parallel to the surface.