Some experimental studies in elastic wave propagation

Abstract

A number of experimental studies of elastic wave propagation in solids, with which the author has been associated, are reviewed. These concern the propagation and reflection of mechanical pulses in elastic solids. In most of these studies, unexpected mechanical response has been observed. The problems discussed include that of a glass beam subjected to flexural loading [H. Kolsky, Dynamic Crack Propagation, edited by G. C. Shih (Noordhoff, Groningen, 1973), pp. 399–414; V. Kinra and H. Kolsky, Eng. Fracture Mech. 9, 423–432 (1977); H. J. Schindler and H. Kolsky, J. Mech. Phys. Sol. 31, 427–437 (1983)] and it has been shown that the time for the fracture to be completed is equal to the time it takes the extensional compressive wave generated by the growing crack to travel to the free ends of the beam and be reflected back as a tensile pulse. Another problem discussed is that of the elastic impact of a sphere on a plate. When the plate is sufficiently thick, i.e., its thickness is such that the sphere separates from the plate before reflected waves reach the region of contact. The problem, which was first treated by Hertz, has more recently been treated by S.C. Hunter [J. Mech. Phys. Solids 5, 162 (1957)], who showed that about 1% of the energy is converted into elastic vibrations of the block. C. Zener [Phys. Rev. 59, 669 (1941)] has shown that the low coefficients of restitution observed for thin plates can be explained in terms of flexural plate waves. More recently, M. G. Koller and H. Kolsky [Int. J. Solids Structures 23, 1387–1400 (1987)] have studied the problem in detail in terms of the propagation and reflection of the waves generated by the impact and shown two unexpected phenomena, namely the propagation of a longitudinal disturbance at the S-wave velocity, and an enhancement of amplitude on reflection of an outgoing P wave. Other studies which will be discussed are the change in pulse shape which occurs when a unidirectional pulse is reflected at the boundary between two noncollinear rods [J. P. Lee and H. Kolsky, J. Appl. Mech. 39, 809–813 (1972)], and between a rod and a half-space [S. Boucher and H. Kolsky, J. Acoust. Soc. Am. 52, 884–898 (1972)].