A Study On Complex Dynamic Properties Of Granular Material

As a typical soft matter, granular materials exhibit solid-like behaviour and fluid-like behavior. The study of granular materials is attractive. In this thesis, many dynamic behaviors of granular materials have been studied, in order to understand the complex behaviour of granular materials. The remainder of this paper is organized into two parts as follows.The first part of this work is the impact response of granular materials which was investigated by experiment with split Hopkinson press bar.In Sec. II, we describe the dynamic mechanical properties of granular materials under confined compression. Based on the modified split Hopkinson press bar and materials test system, the stress-strain relation of dry sand was investigated. And strain rate effect, preloading, particle size and moisture were also been studied. From the results, we found that the strain rate effect is not obvious, and the compression curve can be dividing in two parts, compacted and crushing. Then, from the particle crushing theory and Cambridge model, an empirical formula was proposed. At last, using the PFC simulation method and cluster algorithm, the relation between particle crushing and microstructure was raised.In Sec. Ⅲ, we investigated the dynamic mechanical properties of granular effective medium under combined compression-shear. We present a new combined compression-shear test technique to investigate the dynamic response of materials. It is based on Hopkinson press bar, and applied the desired compression-shear loading by the beveled ends with different angles. The data processing methods are studied and verified by the finite element analysis. A series of experiments on granite were performed. It shows that this method can provide combined compression-shear loading, and achieve a new experimental method to investigate the dynamic mechanical properties of granite under impact multi-axial loadings.The second part of this work is the rheology and viscoelastic of granular materials which was researched by non-equilibrium molecular dynamicsIn Sec. IV, we study the rheology of planar shear flows of athermal granular systems via non-equilibrium molecular dynamics simulations. By applying the simple model without the interference of hydrodynamics and thermostat, we observe the transition from shear thinning to shear thickening. This transition is accompanied with some robust signatures which may not be limited to athermal systems and may thus provide us with a general picture of shear thickening.In Sec. V, we propose to characterize in detail the behaviour of granular materials under oscillatory shear, including the linear viscoelastic and nonlinear viscoelastic. Based on the results, a phase diagram was obtained to describe the mechanical response. And Fourier transforms rheology, stress decomposition method and energy analyses were as tools to analyze the nonlinear viscoelastic.These two parts said that, one is useful for the practical application; another is useful for the physical mechanism of granular material’s motion. We hope this work is helpful for understood the complex nature of granular materials.