| Summary: | 博士 === 國立臺灣科技大學 === 營建工程系 === 91 === This paper uses a numerical analysis method to investigate the influence of characteristics of a particle on properties and behavior of granular materials. The numerical analysis approach is based on three new frames: (1) A new quasi-polygonal particle (QPP) suitable to simulate various particle shapes is used. The shape of the QPP is controlled by only four control parameters, but have the capability to include several shapes of different particles into the particle packing simultaneously by merely varying the values of these four control parameters; (2) A new statistically random search packing algorithm (RSPA) suitable to form a dense packing within a very short time is used. Comparing with other dynamic packing methods with the time-consuming proneness, the proposed algorithm shows an apparent advantage to shorten the time for packing to have a higher degree of applicability; (3) A new systematic method suitable to handily deal with the contact behavior on the particle boundary and estimate the unit normal contact force is used. The contact behavior on intruded boundary for various particles is investigated, including the case of more than one contact points. The result shows that there is a nonlinear relationship between the contact force and intruded depth.
By combining these three above-mentioned frames with the discrete element method (DEM), a new numerical analysis method based on the QPP is formulated. By taking the advantage of numerical simulation and the characteristics of reproducibility on packing, the influence of various particle shapes on properties and dynamic behavior of particle packing is studies by simulation. The results show that the shape of the particle indeed has a obvious effect on the density and fabric characteristics of the particle packing. On static packing, the particle packing composed of uniform particles has a higher initial density and a fabric diagram displaying an “X” pattern. On the other hand, the bigger the difference of the shape of particle away from the round contour, the lower the initial density of the packing will be. The fabric diagram for packing composed of noncircular particles shows a relatively isotropic contour without an obvious slipping plane.
On dynamic behavior of particle packing, lacking of the rotating torque provided by the normal contact force for round particles results in more slipping planes. The particle will show a tendency of rolling rather sliding provided that the shape of particle is distinctly different from the round contour such that the rolling torque can be easily supplied by the normal contact force from such particles. The coefficient of friction and the viscosity of particle will also directly affect the dynamic behavior of particle packing such as the slump and flowability. For the range of coefficient of friction considered in this paper, the influence is not significant , but the influence from the viscosity is relatively large. By assuming the values of slump and flowability are equal to 100% for the packing with a viscosity of 0.08, then, the packing with the viscosity of 0.1, 0.12 and 0.14 shows a value of 60%, 70 and 84% for the slump, and 65%, 74% and 84% for the flowability, respectively. Moreover, although the configuration of particle packing has shown a finite deformation under the compressive test by a downward plate pressure, the overall contour of the fabric diagram still remains its original orientation without too much variation.
Keyword：quasi-polygonal particle(QPP), packing, contact behavior, intruded depth, overlapped area, unit normal stiffness, fabric
|
|---|
