Discrete Element Analysis Of The Buffering Capacity Of Granular Materials To Impact Load

Granular matter is one of the most popular materials in nature. It is closely related to our life, and has been applied in every field, such as agriculture, industry, aerospace, transportation, construction, natural disasters and so on. It not only has the properties of both fluid and solidity, and sometimes also shows some more complex mechanical properties, for instance, the feature of dissipating energy rapidly. Granular matter will be extruded and collided strongly under the impact load, and its energy will be decayed quickly and efficiently which plays a buffering effect to impact load. Therefore, granular matter is the preferred material of damping and energy absorption under general circumstances. Based on the Discrete Element Method and Hertz contact theory, an impact model of a projectile on granular materials is established to reveal the intrinsic mechanism of granules’ buffering capacity, seek the influence factors and develop an in-depth research in this paper. This study will promote the technology of damping and provide a basic theory for its engineering application.Firstly, a model of projectile on granules is established based on discrete element method. The movement law of projectile and the mechanical properties of the bottom plate in different thicknesses of granular matter are analyzed. The factors including thickness, friction and concentration to the buffering capacity are discussed, the internal mechanism of granular matter is analyzed from the perspective of force chain structure and energy consumption, which reveal the relationship among force chain structure, energy dissipating and granular buffering capacity.Secondly, four impact models (disperse granules and bonded granules are packed in random packing and regular packing respectively) are established to analysis the dynamic characteristic of both projectile and plate in this paper. The effect of bond strength to granule’s buffer capacity and the force distribution on plate are investigated which show the transform process from point load to the distributed load from the aspects of micro perspective. The study illustrated that the buffering capacity is closely related with bonded strength and free sliding, explained that granular packing plays a decisive effect on force chain structure.At last, combining with the actual impact environment, this paper introduced the theory of Shock Response Spectrum (SRS) and the conversion method from SRS to time-history excite signal. A SRS from frequency domain to time-history is converted which would be used as an impact load. In order to analysis the buffering capacity of granules to SRS, discrete element models of bonded granules under the impact of the converted load are established. The mechanics responses of both projectile and base plate are calculated, and the influence of the elastic modulus is analyzed. The results show that the bonded granular matter plays buffering effect by reducing the vibration frequency and amplitude of shock excitation, the degree of attenuation is influenced by granular packings and elastic modulus.