The Influence Of Friction Properties On Macro-and Micro-mechanical Characteristics Of Granular Materials

Granular materials are everywhere in the nature world.At the same time,they are widely used in engineering construction.There is a gap between the macro research and the microscopic study of granular materials because that particle system is a typical discrete system.In order to get to the root of the complex characteristics of granular materials,it is important to build bridges between macro-scale and mesoscale.Then,try to find the microscopic mechanism for the macro response.As two extremely important characteristics of granular materials,the friction properties and the critical state are studied in this work.Using DEM,a series of numerical experiments are conducted.The relations between the macro behavior and the evolution of mesoscale structure are analyzed.The results under different sliding friction and rotational resistance properties are also discussed.The critical state of granular materials is researched combining different friction properties.Main findings are as follows:A)Sliding friction coefficient has significant influence on the macro behaviors of granular materials.As sliding friction coefficient increasing,the peak strength and the critical state strength of the specimen increase;The dilatancy phenomenon is more obvious;Void ratio becomes larger and mechanical coordination number decreases;The mobilized friction index decreases.But the change of the sliding friction coefficient has little effect on the normal contact force distribution of the granular system.B)The effect of the rolling friction coefficient on the particulate material is similar to the sliding friction coefficient but they are not exactly the same:With the increase of the rolling friction coefficient,the peak intensity and critical state strength of the specimen increase,the volume strain decreases,the internal friction angle increases,the particle speed decreases,the void ratio becomes larger,the coordination number decreases,the normal contact force increases,and the correctness of the stress-force-fabric model is verified.C)When the particle system is loaded into the critical state,the critical stress under the same mean effective stress increases,the critical void ratio increases and the critical coordination number decreases with the increase of the rolling friction coefficient.The characteristics of the critical state are further illustrated by the strain analysis of the VORONOI mesoscopic unit.D)The macro-scale and mesoscale response have shown a consistent law.It proves that the mesoscale characteristics of the granular material determine the macro-scale behaviors.