Research On Deformation Theory And Dynamic Simulation Of Digging Process For Granular Materials

Granular materials is the object or medium actuated by lots of engineering machinery and bulk solids handling machinery. Digging and breakdown of the granular structure is a major actuating mode or objective in granular engineering. The digging resistance of granular materials affects directly function and efficiency of the working machine in the process of the digging materials. Because of the complicated mechanical behaviors of granular materials, we come up against difficulties in study of digging resistance and its actual engineering application. So that research on the mechanical behavior of granular materials and its digging resistance have important theoretical significance and engineering application value.Aiming at the problem of the digging and breakdown of the materials in granular engineering, this paper has carried out the research in the following three fields: 1. Research on the mechanical behaviors of granular materials and establishment of its constitutive models. 2. Research on the digging resistance of granular materials and establishment of its engineering applicable models. 3. Research on computer simulation models of the grab in the process of its digging the materials and experiment research on process of grab digging the materials. On the basis of the theoretical and experimental research, a lot of the research achievements have been obtained which have theoretical significance and engineering application value. The research contents in detail are following:1). This dissertation analyses the deformation characteristics of granular materials at critical state, and the deformation regulation is derived on the principle of energy equilibrium, i. e. the constitutive relationship of granular material at critical state. This constitutive model describes the non-associated plastic flow of granular material, and replaces the assumption that granular material complies with associated flow rule in the limit" equilibrium theory of granular material. It points out that the principal strain rate is coaxial with the principal stress at critical state and is independent of the critical stress surface. The energy equilibrium equation and the relation between plastic work and thecritical stress surface are given.2). This dissertation presents a hypoelastic constitutive model with four material constants in describing the mechanical behavior of granular materials under loading. Analysis results of the model have good coincidence with those of triaxial experiment of the standard sand under different relative density. The model can describe the contractant and dilatant phenomena of granular materials. A suitable calculation method is given to identify the fore material constants using trialxial tests. In comparison with the hypoplastic constitutive model presented by W. Wu and D. Kolymbas, this model has the advantage of form simplicity. The determination method of material constants presented in this dissertation avoids disadvantage that material constants vary with the chosen reference point.3). This dissertation verifies the applicability of the upper limit theorem and the lower limit theorem in the classical plastic limit analysis theory, and gives correspondingly constrained conditions. The pushing resistance model in digging process is set up. This model has wide-ranging application and simple computing procedure. It avoids the narrow-ranging limitations of slide line method, as well as avoids the complicated computing procedure in the simulation of the gradual breakdown process for the granular structure by FEM. Its analysis results are identical with those of the practical engineering, this model has engineering application value.4). On the basis of affection factor analysis of the pushing resistance in digging process, the dissertation brings up the more simplified resistance model. On the basis of the model, the factor table of the pushing resistance is set up for convenient engineering application. Furthermore some conclusions having engineering application value are obtained:...