Research On Multi-Scale Dynamics And Bearing Mechanism Of Shear Dilatancy For Granular Lubrication

Granular lubrication is a new type of lubrication mode which was put forward according to the granular matter system theory. The basic design idea of granular lubrication is that the hard solid granules as lubricant are directly put into the friction pair clearance. In the process of lubrication, by utilizing microscopic movements such as collision, sliding, friction, rolling between the solid granules, as well as elastic deformation of granule itself, the mutual contact area between friction pair surface and the friction are minimized, and so the friction pairs were protected. Granular lubrication can adapt poor working environment and bear static load. Researching on granular lubrication to mater its multi-scale dynamical features and bearing mechanism of shear dilatancy, which has the important scientific meaning and practical engineering application value.First of all, the governing equation and boundary condition of collision granular lubrication have been deduced basing on supposed two element collision theory. The flow states of collision granular lubrication are researched using numerical method. Numerical results show that the fluctuation of granular lubrication medium between sheared parallel plates is the main factor for inducing changes of solid volume fraction, fluctuation velocity and friction coefficient. Changes of main three body parameters can alter the fluctuation trend of granular lubrication medium, thus cause changes of solid volume fraction, fluctuation velocity and friction coefficient.Next, the theoretical research model of dense granular lubrication has been established between sheared parallel plates by discrete element method. The fluctuation velocity, self-diffusion features, dynamic characters, force chain characters, shear dilatancy phenomenon and bearing mechanical mechanism are researched for the granular lubrication medium. The main research results show that variation tendency of average velocities are opposite to fluctuation velocities. Contact forces and contact angles exhibit a power law behavior and magnitude of normal contact forces are far greater than tangential contact forces. The dynamic behaviors of granular lubrication medium can transform into four states, jamming, quasi-static, slow and rapid flow. Variation of shear dilatancy rates with time steps for granular lubrication medium exhibit a power law behavior in the process of shearing, overall shear dilatancy degree decrease with increasing the shear velocity and increase with decreasing the pressure load. Normal forces generating in the process of shear dilatancy can effectively bear pressure load for the granular lubrication medium.Bearing ability of granular lubrication medium decreases with increasing of shear velocity, and increases with increasing of pressure load, etal.Lastly, the stick-slip motion mechanisms of dense granular lubrication have been studied by experiment based on plane contact tribotester. Experimental results show that macroscopic friction coefficient between the moving friction pair and the granular lubrication medium is closely related to mesoscopic force chains. The evolution rule of mesoscopic force chains decide on the change of macroscopic friction coefficient, and the macroscopic friction coefficient can been seen as macroscopic mirrors for changes of mesoscopic force chains. The rheological behavior of granular lubrication medium can gradually transform form stick-slip state to slip state with increased shear velocity and pressure load.From the above theoretical and experimental study for granular lubrication system, the rheology mechanism, bearing mechanism of shear dilatancy and stick-slip features for granular lubrication is illuminated. On this basis, establish the granular lubrication theory which considered multi-scale dynamics and bearing mechains of shear dilatancy for granular lubrication medium. The research results could supply theoretical support in application and progress for granular lubrication, and also promote the development of granular matter mechanics.