SOLITARY WAVES IN A CHAIN OF BEADS UNDER HERTZ CONTACT

We study experimentally the propagation of high-amplitude compressiona l waves in a chain of beads in contact, submitted or not to a small st atic force. In such a system, solitary waves have been theoretically p redicted by Nesterenko [J. Appl. Mech. Tech. Phys. (USSR) 5, 733 (1984 )]. We have built an impact generator in order to create high-amplitud e waves in the chain. We observe the propagation of isolated nonlinear pulses, measure their velocity as a function of their maximum amplitu de, for different applied static forces, and record their shape. In al l experiments, we find good agreement between our observations and the theoretical predictions of the above reference, without using any adj ustable parameter in the data analysis. We also show that the velocity measurements taken at three different nonzero applied static forces a ll lie on a single curve, when expressed in rescaled variables. The si ze of the pulses is typically one-tenth the total length of the chain. All the measurements support the identification of these isolated non linear pulses with the solitary waves predicted by Nesterenko.