Papers by Author: Dong Min Yang

Abstract: Damage and failure of the fiber reinforced composites remain as a challenging research subject in the area of material science and engineering. In this study a novel particle assembly model is developed using two dimensional Discrete Element Method (DEM) for the purpose of simulating the damage and failure process of the single-fiber composite (SFC) under axial tension. Fiber (SiC) and matrix (Epoxy) are represented by particles bonded together through elastic parallel bonds which are calibrated by a series of numerical tests. The contacts between the fiber particles and matrix particles are directly accounted for the fiber/matrix interface which is represented by the contact softening model similar to the cohesive zone model (CZM) in the continuum mechanics. The single-fiber composite tensile test is carried out using the developed DEM model in order to evaluate the interactions between fiber breakage, interfacial debonding and matrix cracking. The numerical results have demonstrated the capability of the developed DEM model in simulating the entire failure process of each individual constituent of the single fiber composite. This study has also confirmed that the DEM model has unique advantages over the conventionally numerical models in terms of dealing with the evolution of microscopic damages in composite materials.

Abstract: Based on the theory of metal pre-stressing machining, the method of pre-stressing suitable for ceramic materials machining was presented. Using the cluster method, the discrete element method (DEM) model of ceramic materials machining was established. The DEM simulations of cutting process of SiC ceramic under different machining parameters were carried out by orthogonal test design method, and the effects of machining parameters on the number of surface cracks and maximum crack depth after processing were also analyzed. The results showed that the tool edge radius influenced greatly on the number of surface cracks, while the pre-stress influenced greatly on the maximum crack depth.

Abstract: In this paper, the technology of pre-stressed machining suitable for ceramic materials was presented. Using the cluster method, the discrete element method (DEM) model of SiC ceramic was established to simulate the crack’s initiation and propagation in cutting processes with different pre-stress value. The scratching tests were carried out to confirm the validity of simulation. Both the DEM simulation and the experimental investigation showed that: with the increasing of pre-stress, the number of radial cracks reduced and the transverse cracks replaced the radial cracks to some extent, and also caused the material removal in the form of smaller fragments. Using pre-stressed machining can decrease the machining damage and improve the surface quality, and further prove that using DEM to simulate the machining process of ceramic materials was feasible.

Abstract: The mechanical models formed by packed circular discrete elements were used to investigate the mechanical properties of Si3N4. In these models, the distribution of elements is random in the specified region, and the average radius of elements is 6m. The main mechanical properties investigated here are Young’s modulus, compressive strength, Poisson’s ratio, fracture toughness and bending strength. Some numerical simulation analysis of the size effect of the mechanical properties in these discrete element models were carried out. The simulation results suggest that there is no obvious size effect for Young’s modulus, compressive strength and Poisson’s ratio in these discrete element models. However, for bending strength, when the number of elements in model is less than about 9000, there exists obvious size effect, with the increasing of the number of the elements, the size effect will become less and less until disappeared. The value of fracture toughness decreases with the increasing of the number of the model elements. The classical continuum fracture mechanics model about material fracture under tensile stress is also established by discrete element method. The simulation results are just the same as the simulation results of single edge notched bending (SENB) and the experimental values reported in other literatures. The results provide a more reliable foundation for the application of DEM in simulating the mechanical behaviors of advance ceramics.