Research on Transient Wave Propagation Across Nonlinear Joints Filled with Granular Materials

Abstract

A nonlinear thin layer interface model overcoming the long-wavelength assumption of displacement discontinuity model is developed to analyze the full-wavelength wave propagation across nonlinear parallel joints. In this study, the filling material is treated as a thin layer with reduced mechanical properties to reveal multiple reflections and time shifting within the filled joint. The nonlinearity of the filling material is considered, and a recursive matrix is derived in time domain. An experimental study on wave propagation across a filled joint was carried out by SHPB test. The quartz sand layer of different filling thicknesses sandwiched between Hopkinson bars was pressured by compressional waves to investigate the wave attenuation. Comparisons of the joint thickness, the wave frequency and the incident angle are carried out between the present model and the existing displacement discontinuity model. The results indicate that the thin layer interface model considering the thickness of the joint is capable of extending the long-wavelength assumption to full-wavelength research and it is more appropriate for filled joints with thick thickness that is comparable to wavelength. Then, this model is extended to parallel joints, and the properties of the filling material (i.e., initial elastic modulus and maximum closure), impact velocity, incident angle and wave frequency on wave attenuation are discussed for a joint set. The spacing dependency of the transmission coefficient for parallel joints is compared with displacement discontinuity model.