Mesomechanical Properties Of Two-dimensional Multilayer Composite Particle System

A large number of discrete particles form a granular system through contact interaction,and the multi-scale and multi-media of granular materials lead to a granular system with complex mechanical prope.In this paper,aiming at the two-dimensional multilayer composite particle system under different loads,taking the mechanical response at the bottom of the particle system,the internal force chain network and interlayer shear stress and other mesomechanical properties as the starting point,the influence of loading mode and particle layer number on the internal mechanical response of the system is analyzed and discussed by using the discrete element research method,and finally a four-layer composite particle system is established in combination with the actual engineering to verify the correlation and analyze its mechanism from the perspective of meso-mechanical properties.The main conclusions are as follows:(1)In a monodisperse regular granular system,the concentrated load action will cause more force to be transmitted to the bottom area of the particle system and to the boundary with minimal transfer.The bottom peak force and the bottom average force under impact load are smaller than when subjected to concentrated load,but the proportion of the intermediate particle force to the sum of the bottom forces is larger,and the peak force is closer to the middle loading part.In the case of double loading,the change of the number of particle layers will lead to a large dissipation of force,making the particle system more robust and not easy to be destroyed,double loading can improve the distribution of the particle system.(2)The distribution of force at the bottom of the two-dimensional random particle system is more uniform,and the internal dissipation is greater when the force is transferred from the top of the system to the bottom.In the case of single and double loading,the average bottom force under impact load is significantly smaller than the bottom force under concentrated load.The loading method has a large change on the bottom force of the system,and the increase of the number of layers has little effect on the bottom force.As the number of layers in the particle system increases,the strong chain distribution is more uniform.The double-loading scenario is more secure and stable than the single-loading scenario.(3)Under the condition of double loading,the concentrated load action can significantly reduce the magnitude of the interlayer shear stress.In addition,with the increase of the number of layers of the system,the maximum interlaminar shear stress at the top and the maximum interlaminar shear stress at the bottom of the one-to four-layer particle system both decrease at the corresponding positions,which also helps to reduce the deformation performance of the system,so that the system is safer and more stable.(4)The changes in permeability and transfer efficiency of the three-layer particle system under the double-loading impact load show that the soft particle interlayer can effectively resist the double-loading impact load and make the failure more less likely to occur.Under double-loading impact load,the three-layer particle system has the best force transfer effect,while under concentrated load,the three-layer particle system has the worst permeability and the lowest force transfer efficiency.(5)As the loading position shifts to the right,the upper overall force chain and the strong chain will be significantly shifted to the right,while the lower force chain will hardly change.The loading interval has little effect on the evolution of the overall force chain,but when the loading interval is small,the strong chain inside the system will be very dense,and as the loading interval increases,the strong chain inside the system will become sparser.(6)The direction and magnitude of interparticle shear stress in the system change rapidly with the change of loading position and loading interval,and the maximum shear stress of the upper,middle and lower layers all show a trend of first decreasing and then increasing and then decreasing and then increasing.At the same time,the loading interval has a significant effect on the maximum interlaminar shear stress of the lower layer,which will lead to the weakening of the deformation performance of the system.However,there is no obvious law to follow the effect of loading interval on the maximum interlaminar shear stress of the middle layer and the upper layer.With the change of loading position,the change law of vertical average displacement is similar to the change law of maximum shear stress between layers,while with the change of loading interval,the change law of vertical average displacement is different from the change law of maximum shear stress between layers.