Research On Unsteady State Behavior Of Restricted Granules In Frictional Interfacial Micro-fields

The non-steady state of particulate matter is an important research direction at the microscopic scale.It often affects the nonlinear response of macro-mechanical response and macro-friction coefficient directly.It has important research value and significance in the field of soil mechanics and tribology.So,the research background of this subject is based on the characteristics of granules unsteady behavior in restricted space.Because the complexity of particle movement in microscopic is hard to be observed experimentally,therefore,finite element method is used to study the mechanical behavior between granules and interface,and preliminary explore the change of the force chains shape and the microscopic movement of the granules in restricted space.First of all,a two-dimensional finite element model of granules in interface-restricted space is established to simulate the movement process of granules under different loads,contact friction coefficients and velocities of the lower surface.The results show that with the increase of load,the contact friction between the granules and the lower surface increases gradually.And friction has been in a state of fluctuation,which is a manifestation of non-steady state.Friction and speed are not directly proportional relationship,but there is a similar "polarization" of the law,that is,at high speed and low speed,the friction is relatively large,and moderate speed,the friction is small.Secondly,in order to reflect the unsteady characteristics of particles more clearly,this paper also analyzed the effect of speed,load,friction coefficient on the granules and the upper and lower surface velocity displacement fluctuations.At the shearing stage,the granules displacement begins to increase continuously.As the load increases,the displacement difference between the granules also increases.Granules movement is gradually increased without law.Under different loads,the velocity fluctuations of the elastic granules show more intense fluctuations at both ends,while the weak fluctuations in the middle.In addition,the influence of the friction coefficient on the displacement of the upper surface in the x-axis direction produces a "W"-type trend,but the change of the friction coefficient has less effect on the variation of the displacement.As the velocity increases,the effect of velocity on granules displacement also shows "polarization".The research shows that the frictional dissipation energy and kinetic energy of the model are basically proportional to the load and slip velocity.The dissipation of energy is mainly due to the energy change of the force chain.The slip and rotation of the granules lead to the slippage or rotation of the surrounding particles,so that the strong chains are weakened or broken.The increase of kinetic energy basically corresponds to the release of elastic potential energy.When the kinetic energy changes intensely,the shear band begins to appear.Small loads,as well as smaller and larger speeds,can adversely affect the granules unsteady behavior,whereas larger loads and speeds,but not to a certain degree,can make granules in restricted spaces better isolated the contact surface between asperities,to achieve the lubrication effect.Granules non-steady state is also weak.In practical engineering applications,the optimal steady state can be achieved by appropriately adjusting the load bearing of the surface and the relative sliding speed between the interfaces.Finally,the force chain morphology evolution and microscopic movement of particles were studied."U-shaped" chain and ring-shaped chain similar,are extremely unstable.The strong chain surrounded by some weak force chains is in a relatively stable structure.At the same time,the rotational movement of the granules in the shear band is also consistent with the granules contact movement model.