A Study On Tuning Mechanical Response In Granular Systems

Granular system is a complex system composed of a large number of particles,which is widely found in nature and closely related to people's production and life.The inelastic collisions and frictions between the discrete particles that make up the particle system cause many unique mechanical behaviors.Researching on these behaviors has always been one of the leading topics that mechanics and physics are paying close attention to.Due to the complexity of the granular system,its mechanical response under external forces has not been clarified.In addition,because of the ubiquity of granular systems,it also requires the artificial regulation and intervention of the system's mechanical response under external forces in order to make better use of it.In this paper,the mechanical properties of the particles,such as hardness and the distribution characteristics of the particle system have been experimentally studied in the change of the system's mechanical behavior by using the classic photoelastic experiment method,and some meaningful results have been obtained,as follows:First of all,in the traditional study of the granular systems' mechanical behavior,the average square gradients and external force,i.e.the ?G ?-F curve of the granulars are given by the diameter-compression mode without taking account of the impact on the results caused by force configuration of the particles.In order to solve this problem,we have applied different amounts of forces to photoelastic test pieces.For example,we have adopted 2-point compression,3-point compression and 4-point compression modes.As a result,we have obtained corresponding calibration curves between the average square gradients and the external forces by considering the force pattern of the particles.The results show that the traditional calibration curve for diameter compression does not have universal adaptability,and the contact force given by it is higher than the value obtained by using the calibration curve,which have taken force pattern into account.This also shows that in the study of the mechanical behavior of granular systems,it is necessary to identify the force pattern of particles in the first place,and then use a reasonable calibration model to quantify the contact force.Then,for the granular systems consisted of "soft" and "hard" particles,the experimental results show that when they are subjected to local quasi-static external forces,the force chains tend to propagate in "hard" particles.This is consistent with the theoretical calculations in the literature.In addition,experiments have been conducted by placing some “soft” particles in a “hard” particle system.The results show that the introduction of “soft” particles can effectively change the propagation path of the force chains,and the introduction of “soft” particle groups will change the overall mechanical behavior of the system.Finally,this paper makes a preliminary exploration of the mechanical response of granular system under impact loading.The stress wave propagation velocity in the "soft" particle system under initial prestress was measured.The results show that the initial prestress can promote the propagation speed of the stress wave.In addition,the variation of stress wave propagation characteristics induced by the introduction of "soft" particle layers in the particle system was studied.The results show that the introduction of "soft" particle layers can inhibit the transmission of stress wave.