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摘要
Both continuum and discrete methods are used to investigate the soil cutting process. The Discrete Element Method (DEM) is used for the discrete modelling and the Material-Point Method (MPM) is used for continuum modelling. MPMis a so-called particle method or meshless finite element method. Standard finite element methods have difficulty in modelling the entire cutting process due to large displacements and deformation of the mesh. The use of meshless methods overcomes this problem. MPM can model large deformations, frictional contact at the soil-tool interface, and dynamic effects (inertia forces). In granular materials the discreteness of the system is often important and rotational degrees of freedom are active, which might require enhanced theoretical approaches like polar continua. In polar continuum theories, the material points are considered to possess orientations. A material point has three degrees-of-freedom for rigid rotations, in addition to the three classic translational degrees-of-freedom. The Cosserat continuum is the most transparent and straightforward extension of the nonpolar (classic) continuum. Two-dimensional DEM and MPM (polar and nonpolar) simulations of the cutting problem are compared to experiments. The drag force and flow patterns are compared using cohesionless corn grains as material. The corn macro (continuum) and micro (DEM) properties were obtained from shear and oedometer tests. Results show that the dilatancy angle plays a significant role in the flow of material but has less of an influence on the draft force. Nonpolar MPM is the most accurate in predicting blade forces, blade-soil interface stresses and the position and orientation of shear bands. Polar MPM fails in predicting the orientation of the shear band, but is less sensitive to mesh size and mesh orientation compared to nonpolar MPM. DEM simulations show less material dilation than observed during experiments.
- 出版日期2014-12
