Physical And Numerical Study On The Vibrated Packing Densification Of Regular Tetrahedral Particles

Based on the situation of insufficient studies on packing of non-spherical particles,regular tetrahedra in current study are chosen as the research target.And systematic physical and numerical experiments are carried out to reproduce the packing densification of regular tetrahedral particles when subjected to mechanical vibrations,where in numerical work the molecular dynamics based discrete element method(DEM)is used for dynamic simulations.The researches are mainly focusing on:(1)Identifying the influences of operating parameters such as vibration conditions(including vibration time,amplitude,frequency and vibration intensity)and boundary conditions(container size and container wall)on packing densification,obtaining the optimal processing parameters,and validating the numerical results by physical experiments;(2)Numerical and physical realization of dense random packing structures(amorphous states)of tetrahedral particles,followed by the analysis and characterization on corresponding macro-property such as packing density or porosity and various micro-properties such as coordination number(CN),radial distribution function(RDF),orientation,contact network,and force distribution.The work in this thesis can on the one hand effectively compensate current research gaps in the packing densification of tetrahedral particles,and on the other hand the obtained dense amorphous packing structures have theoretical and practical meanings not only for the new particulate materials in scientific research but also for many key areas in industry such as materials,metallurgy,and chemical engineering etc.The results indicate that:(1)In both the numerical simulation and physical experiments,the influences of vibration conditions on macro properties of regular tetrahedral packing systems have similar trends.I.e.the packing density increases with the amplitude A or frequency ? to a maximum and then decreases.The role of A or ? in the packing densification can be ascribed to the vibration intensity effects.Increasing ? means the input of external energy into the packing which will densify the packing structure.However,too large or small ? is not helpful for densification.Meanwhile,no one-to-one relation between p and ? implies that we cannot simply use a single ? to characterize the packing densification,A and ? should be considered concurrently.(2)In physical and numerical experiments,the maximum packing densities through extrapolation to eliminate container size effects can reach 0.747 and 0.743 respectively,which indicates good agreements between physical and numerical results and validates the accuracy and effectiveness of the applied numerical model in DEM simulation.(3)The CN distributions obtained in DEM numerical simulation show the peaks of 6 for initial loose packing and 8 for vibrated dense packing,respectively.The shift of the curve to the right indicates that the input of the external energy can realize the transition of packings from random loose to dense.In addition,the two structures also give different RDF distributions.Compared with the initial packing structure,the vibrated dense structure has the features of random close packing.I.e.a high peak appears at the minimum possible distance of two adjacent particle centers,which corresponds to these two particles with a face-face contact.While at a longer distance,no obvious peaks can be observed,which indicates that the particles are distributed uniformly and the structure is random enough.(4)The orientation distribution and the contact network of the numerically generated loose and dense structure also prove the randomness of the packing structure of regular tetrahedral particles.And the differences of the magnitudes and distribution of forces in these two structures demonstrate external energy influence on the packing densification.