Transformation of a Longitudinal Elastic Wave into a Pochhammer Wave

The paper reports on a dynamic finite element simulation of the propagation of longitudinal elastic waves in cylindrical plates and Pochhammer waves in rods. The simulation shows that in cylindrical specimens of compact shape, a single longitudinal wave first propagates till unloading waves from their lateral surfaces start to interact, and then, two types of longitudinal elastic waves propagate at a time. In rods, first comes a longitudinal elastic wave, and then, two concurrent waves—a longitudinal elastic wave and a Pochhammer wave—due to the effect of unloading from their lateral surfaces. With the example of aluminum, it is demonstrated in which range of geometric parameters the elastic properties of near-compact specimens cannot be analyzed by ultrasonic methods.