| Granular matter is a complex system composed of a large number of interactional solid particles.It has important application value for the study of granular matter,which improves the processing technology of granular matter,the cognitive ability of the formation and evolution of natural disasters,and the mechanism of disaster prediction.The propagation path of contact force between particles is called the force chain.The description of the force chain and evolution law of the force chain is one of the most important cores in the study of granular matter,and the study of the contact force between particles is the basis of the study of the force chain.So it is of great significance for the study of granular matter.Experiment and numerical study were researched in this paper,and the contact force between particles and its propagation law were studied.The research idea of this paper was based on the three-dimensional digital image correlation method,then the change of particle contact force under different external forces was studied.The discrete element numerical simulation method was used,and this paper compared simulation results with experiment results.Then the correct simulation parameters were got by trial and inversion.Finally,the internal force chain of granular system was obtained.The specific research work and conclusions are as follows:In the experimental aspect,the 3D digital image correlation method was applied to the study of the contact force in the granular system for the first time.In this paper,the study of the contact force in the granular system by using the digital image correlation method of two-dimensional space expanded to three-dimensional space.Based on the principle of binocular stereo vision,3D digital image correlation method was used to solve the limitation of 2D digital image method for measuring the deformation of objects in the plane.Specific test plans were designed,and by using a transparent material and adding a refractive liquid method,the key problem of the occlusion between the boundary and the particle was solved.And the advantages of non-contact and full field measurement of 3D digital image correlation method were given.The contact deformation between particles in the granular system was obtained.From the basic idea of copying paper mark method,the calibration experiments of ball and plate as well as ball and ball were carried out,and the corresponding relation between the contact deformation and the contact force was established.Finally,the contact force between particles in the granular system was obtained.In numerical simulation aspect,because the characteristics of the particles in the simulation were real particles,Hertz-Mindlin contact model was used.Then the macroscopic elastic modulus and Poisson's ratio of the material were used for describing the contact stiffness,and the difficulty of determining some calculation parameters was solved.For the problem of uncertain friction coefficient,the results obtained from the trial and inversion by comparing the simulation results with the experimental results.The obtained parameters were validated with tests of other granular system,and the correctness of the mesoscopic parameters was proved.Finally,according to the correct calculation parameters,the force chains in granular system were studied numerically.Based on the numerical simulation of the mesoscopic parameters,the internal force chain about two structures of the whole granular system was obtained under exterior load.These two structures were the Spatial arrangement structure of body-centred cube and the Spatial arrangement structure of random.And the distribution of the force chain was analyzed.The following conclusions were obtained:?The transmission of force in granular system is divergent;?In the granular system,the direction of the main chain is the direction of external force;?In the same plane along the direction of the external force,the particles in the middle part bears the main external force. |
PDF Full Text Request