Study On Force Chain Of Two-dimensional Photoelastic Particle System Based On G~2 Value Method

The particle system is a complex and large system,which is not only closely related to human life,but also related to the safety of people’s lives and property in nature.From a macroscopic point of view,its behavior can sometimes behave in a stable manner,while at other times it can change due to very small effects and show powerful explosive forces,such as collapse,and from a microscopic point of view,the internal behavior of a system formed by the interaction of a large number of single particles is again extremely complex.For the exploration of particulate matter,starting from the macroscopic scale of the particle system and the microscopic scale of a single particle alone does not achieve the expected results,and it is often necessary to establish the connection between the two from the fine scale of the force chain,which is the path of contact force transfer between particles and is a relatively stable structural body existing inside the particle system.In order to investigate the evolution of the internal mechanical behavior of the particle system,this paper uses a two-dimensional photoelastic experiment method and combines digital image processing technology to extract the geometric information of the particle material,calculates the inter-particle contact force and obtains the distribution of the force chain using the G~2value method,and analyzes the changes of the average coordination number,contact vector angle and the distribution of the contact force of the particle system under different vertical loads,and observes the evolution of the strong force chain under vertical loads by obtaining the distribution of the internal force chain of the particle system.The information on the angular distribution of the force chain direction and the change of the force chain length were counted,and the fracture and reorganization of the force chain at different loading moments were analyzed.The experimental model of two-dimensional particle system under vertical load was constructed by using PFC numerical simulation software,and the changes of velocity field,displacement field and force chain of the particle system at different loading moments were analyzed.The following aspects are mainly carried out:(1)Read domestic and foreign research materials related to the topic,and summarize the current development of experimental techniques for particulate matter,force chains,and photoelasticity.(2)Based on the basic principle of the photoelastic experimental method,two-dimensional photoelastic particle compression experiments were carried out for the same diameter particle system with the same thickness and the mixed diameter particle system with different thickness under vertical loading,and the photoelastic images at different loading moments were collected by digital cameras to study the effects of different factors on the internal mechanical behavior of the particle system.(3)The basic principle of G~2 value method is introduced,and the photoelastic particle images under step-by-step loading are obtained through calibration experiments,combined with Matlab program to calculate the G~2 value corresponding to the photoelastic particle images at each loading moment,and fit and analyze the relationship curve between G~2 and the average contact force F.Based on the obtained G~2 value of each particle,the contact force of the particle system subjected to vertical loading is calculated.(4)The geometric position information of the particle system obtained from the photoelastic experiment was extracted by digital image processing.The change rules of the average coordination number and contact vector angle of the particle system under different vertical loads were analyzed.Based on the average contact force variation table and contact force frequency distribution curve,the variation of contact force distribution of the same diameter and mixed diameter particle system under different vertical loads was investigated.(5)The criteria for discriminating the strong and weak force chains and the identification method of the strong force chains are introduced,and the distribution rules of the particles located on the strong force chains and the evolution of the force chains in the system of particles of the same diameter and mixed diameter under different vertical loads are analyzed.The mechanical parameters related to the strong force chains are calculated and the fracture and reorganization of the strong force chains at different loading moments are analyzed.(6)The PFC-2D software is used to simulate the two-dimensional particle system compression experiment under vertical load,to discuss the velocity field and displacement field that are not explored in the photoelastic experiment,to compare and analyze the force chain formed by the particle system in the photoelastic experiment and the computer simulation experiment,and to supplement and improve the data of this experiment.