中文摘要：

在冲击荷载作用下，颗粒材料通过颗粒间的摩擦及非弹性碰撞可有效进行能量耗散实现缓冲作用．本文采用离散元方法对冲击载荷下颗粒材料的缓冲过程进行数值分析，研究不同厚度下颗粒材料的缓冲性能．计算结果表明：颗粒层厚度日是影响颗粒材料缓冲性能的关键因素，并存在一个临界厚度风．当H〈Hc时，冲击力随日的增加而降低；当H〉Hc时，冲击力对日的变化不敏感并趋于稳定值．此外，在不同颗粒摩擦系数和初始密集度下对缓冲过程的离散元分析表明，光滑和疏松颗粒材料具有更好的缓冲性能．最后，对颗粒材料在冲击过程中的力链结构和底板的压力分布进行了讨论，以揭示颗粒材料缓冲性能的内在机理．

英文摘要：

As a typical energy dissipation system,granular material acts as a buffer under the action of impact load,with absorbing and dissipating energy effectively through the sliding friction and viscous contacts between particles.In this paper we study the buffer capacity of granular material under impact load,by the discrete element method（DEM）.The spherical elements are filled randomly into a rigid cylinder under the action of gravity.A spherical projectile with a certain initial velocity drops into the granular bed from a given height.The impact loads on the projectile and the rigid bottom plate of cylinder are both obtained with DEM simulations.The simulated impact loads on the bottom plate are compared well with the physical experiment data.The influences of granular thickness,sliding friction and initial concentration on buffer capacity are investigated under the impact of spherical projectile.The DEM results show that granular thickness H is a key factor for buffer capacity.In the DEM simulations,the impact load on bottom plate presents unique characteristics under various granular thickness values.With granular thickness increasing from zero,a transition from one peak to two peaks takes place,then the two peaks return to one peak in the time curve of impact load.The evolution of impact load peak with its temporal interval is discussed.A critical thickness Hc is obtained.The impact force decreases with the increase of granular thickness when H 〈Hc,but is independent of the granular thickness when H〉 Hc.Moreover,the impact forces are simulated under various sliding friction coefficients and initial concentrations.It is found that the smooth and loose granular material has more effective buffer capacity.Finally,the spatial structures of force chains and the distribution of impact forces on bottom plate are discussed to reveal the mechanism of buffer properties of granular material on a micro scale.