Study On The Force Transmission Mechanism In Two-dimensional Double Dispersed Granular Stacks Under Concentrated Load

In this paper,the bottom force distribution curve in the granular deposit is taken as the entry point,the experimental method using aluminum-plastic composite board combined with carbon paper technology and the simulation method based on discrete element method are mainly used for the force of the double-dispersed granular stacks under concentrated load.The force transmission mechanism was experimentally studied and numerically simulated to compare the changes in the bottom force and the internal force chain contact network of monodisperse,upper and lower soft and hard layered,left and right soft and hard layered,and sandwich granular system with intermediate interlayer.The influence of friction coefficient on the force transmission mechanism of the granular system is further discussed.The innovation point is to design and process a new experimental model and analyze the bottom force distribution of the double-dispersed granular system.The phenomenon at the bottom"force gathering"is observed for the first time.When the concentrated load is transmitted in the two-dimensional monodisperse granular system,both the experimental and simulation results show that the bottom force curve is a symmetric bimodal curve,but the simulated curve amplitude and bottom average force are smaller,and the peak position is closer to the center point.When the particle stiffness factor decreases,the bottom force also decreases.In the experiment,the peak and average force of the soft particles were only about 60%of the hard particles;in the numerical simulation,it was83%.After the stiffness coefficient of the particles is reduced,the transverse network near the point of action of the concentrated load and the boundary between the two sides changes from the original disconnected state to the connected state.In the upper soft and lower hard double-dispersed particle system,when the force is transmitted from top to bottom,the distribution curve of the bottom force is a symmetric bimodal distribution curve in both experiments and simulations,and the bottom force is greater than the total soft particle system.In the experiment,the bottom average force,peak value,intermediate position force and positional force on both sides increased most when the hard layer thickness ratio was about 0.7-0.8,resulting in 2.33 to 5.65 times of the original system.In the numerical simulation,as the hard layer thickness ratio increases,the average force at the bottom increases linearly with the peak value,and the intermediate position force has a minimum value at?₁=0.45,which is 89.35%of the total soft particle system.After the side position force is?₁>0.2,it fluctuates slightly around 0.61N-0.67N,and the contact of the particles near the left and right boundaries is gradually opened,and tends to the full hard particle system.The contact at the left and right boundaries of the lower half is?₁>0.2.After its lateral disconnection area is almost unchanged.With the increase of soft layer thickness ratio,the bottom forces in the upper hard and lower soft double-dispersed particle system in experiments and simulations are evolutioned according to bimodal distribution?platform distribution?monomodal distribution?bimodal distribution curve.In the experiment,the average force and peak value at the bottom are smaller than those of the full hard particle system,and the intermediate position force and the position force on both sides fluctuate around the value of the original full hard particle system.In the numerical simulation,the average force decreases linearly with the increase of the soft layer thickness ratio.The peak and intermediate position forces have the maximum value at?₂=0.45,and the positional forces on both sides increase first and then decrease,and decrease to 0.5,fluctuate between 0.45-0.5N.In the left and right laterally layered bi-dispersed particle systems,the contact force is more likely to accumulate on one side of the hard particles.Whether the concentrated load is transmitted from the hard area on the right side to the weak area on the left side or from the weak area on the left side to the hard area on the right side,a more obvious strong main force chain is formed in the right hard particle layer,and the bottom force is distributed.When the soft column thickness ratio or the hard column thickness ratio is equal to 0.2,it becomes a right single peak distribution.In the contact network,as the soft?or hard?particle layer increases,a stable effective connection region is formed in the left soft particle region,and a stable triangular break region is formed at the soft and hard interface of the hard particle region.The bottom force distribution curve of the sandwich type bi-dispersed particle system with a weak interlayer in the middle still maintains a bimodal form similar to the full hard particle system.When the weak interlayer is kept in the middle area and the thickness changes,the bottom average force and the positional force on both sides of the experiment are generally larger than the value of the original full hard particle system,while the peak and intermediate position forces are exactly opposite;the average force in the simulation is When the thickness of the interlayer exceeds half of the total number of layers,it is reduced to about 40%of the total hard particle system.When the thickness of the interlayer is constant and the position changes,the average force at the bottom,the peak value,the intermediate position force,and the positional force on both sides are related to the thickness of the weak interlayer.The intergranular friction coefficient?₁ will obviously affect the transfer of contact force in the particle system,and the friction coefficient?₂ between the wall and the particle hardly affects the transmission of the contact force.When the intergranular friction coefficient?₁ is small,the force chain will be transmitted along two main chains distributed in an equilateral triangle.After the force chain is transmitted to the bottom,the bottom contact force is bimodal;when?₁ is large,the force will be in the middle.Offset,the bottom contact force will exhibit a unimodal distribution.Intergranular friction increases the elasticity,making the internal stress distribution more satisfying the elliptic equation.