Introduction of Adhesive Force to DEM Simulation and Application to Fracture of Fragile Powder Materials

We introduce an adhesive powder model based on the discrete element method (DEM). By using this model, we investigate how fragile substances consisting of a lot of adhesive powders, powder materials, are fractured. In the powder material, the powders have a weak attraction and are stuck to each other by adhesion. Thus, the powder materials are easily broken by the external force. We investigate the crack morphology of the fractured powder materials by changing two parameters expressing the strength of the adhesive force χ and width of the powder size distribution Δ. The fracture pattern is changed from cracking to crumbling as Δ increases for every χ value. Interestingly, we find that this change seems to start at a particular point of Δ from observations of the fractal dimension of the cracks Df versus Δ. This result may suggest that the morphological change of the cracks may be related with a transition in the granular systems such as the glass transition.