Study On The Mechanical Response Of The Existence Of The Weak Zone To The Two-dimensional Particle Accumulation

The macroscopic mechanical behavior of particulate matter is closely related to its microstructure and microscopic interactions between particles.Therefore,to study the mechanical response characteristics of a particulate system under external loads,it is necessary to conduct detailed discussions with experiments and numerical simulations at the same time.This paper takes the bottom force distribution curve in the particle accumulation as the starting point,adopts the experimental method of aluminum-plastic board combined with carbon paper technology,and discusses the influence of the existence of the weak area on the force transmission mechanism in the particle system by changing the parameters of different weak areas.At the same time,the corresponding discrete element simulation is carried out on the basis of the experimental scheme,and then the transformation law of the mechanical response characteristics of different composite particle systems is explained from multiple angles.This article mainly focuses on the size,shape,stiffness and location of the weak area.In the discussion of the influence of the size of the weak area,a particle system with triangular weak areas was constructed,and the weak area located in the middle of the system was expanded year-on-year to obtain the force of the particle accumulation under different sizes of weak areas.The experimental part mainly discusses the bottom force distribution state,average force and the change law of the peak value of the composite particle system.From it,we found the bottom force phase drop phenomenon,the peak shift phenomenon and the contact force diffusion law.Numerical simulations found that the average bottom force decreases parabolicly with the increase of the weak area,and the peak value decreases exponentially.At the same time,it reveals the law of contact force diffusion from the perspective of the evolution of the force chain network.The analysis of the forces at different depths of the pile reveals that the larger the weak area,the stronger the lateral spread of the force in the weak area,and the greater the load on the walls on both sides.In the discussion of the influence of the size of the weak area,both experiments and simulations show that as the size of the weak area n increases,the bottom force of the particle system containing the triangular weak area is always bimodal,and the bottom peak and average force decrease accordingly.In the numerical simulation,the average bottom force decreases parabolicly with the increase of the weak area,and the peak value decreases exponentially.The internal force chain distribution shows that as the size increases,the lateral diffusion caused by the weak area increases in the upper layer of the stack.The force chain reorganizes in the area enclosed by the two main force chains with a 60 degree inclination angle to the horizontal,and gradually forms the main force chain.Parallel to the adjacent secondary main force chain,the peak value of the bottom force is shifted.The contact force inside the accumulation body is below 20 mm in depth,and it is bimodal at the same depth layer.The peak profile line gradually turns from parabola to triangle with the expansion of the area size n,until n=6,it becomes a bell Type distribution.The average force of each layer rises stepwise as the depth H increases,and the edge average force rises in a broken line shape,and the larger the n,the smaller the average force,and the greater the edge average force.In other words,the larger the size of the weak area,the stronger the lateral spread of force,and the greater the load on the left and right walls.In the discussion of the influence of the shape of the weak area,a six-sided model and a triangle model are selected for comparison.The weak area occupies a relatively small area,and the bottom force distribution of the six-sided model and the triangle model is not much different;when the occupancy is relatively large,the six-sided model changes from a bimodal distribution to a "flying bird" distribution,and the triangle model maintains the bimodal distribution unchanged.Different from the triangle model,when the size of the weak area is larger in the hexagonal model,there is no obvious main force chain and secondary main force chain at the bottom of the stack.In addition,the average bottom force and peak value of the triangular model at the same depth are always greater than that of the hexagonal model with similar weakness.When the area of the weak area is the same,the hexagonal influence has a wider range of force chains,and the corners of the area are closer to the main force chain or involve the main force chain,which has a greater impact on the transmission of force.In the discussion of the influence of the location of the weak area,two sensitive locations at the bottom of the system and the main force chain are selected for comparison.Experiments show that the weak area at the bottom has a stronger absorption effect on force,and the weak area at the main force chain has a stronger hindrance and diffusion effect on the transmission of force.The higher the weak area along the main force chain,the easier it is for the force to gather on the right peak.The simulation results show that the position change of the weak area from the middle to the bottom will mainly have a greater impact on the middle and lower layers of the particle accumulation.The contact force inside the soft particles in the bottom weak model is smaller than that in the middle weak model.When the weak area is moved from bottom to top at the main force chain,the area where the contact force spreads laterally moves upwards,and the offset force gradually increases.The higher the position of the weak area on the main force chain,the stronger the ability to change the direction of the lateral contact force transmission.