Molecular Dynamics Simulation Of Resonance Caused By Friction At Micro Scale

With the rapid development of micro / nano electromechanical system technology,people’s research on Tribology has changed from macro scale to micro scale.Although the research on Tribology has been very mature at the macro scale,the cognition and understanding of friction at the micro scale is still insufficient.This paper mainly studies the friction characteristics at the micro scale and the vibration phenomenon caused by friction.The main contents and results are as follows:Firstly,a single rough peak contact model composed of diamond tip and monocrystalline silicon substrate is established.The change of monocrystalline silicon substrate with external load is studied by molecular dynamics simulation.It is found that with the increase of load,the silicon substrate changes from elastic deformation to plastic deformation and then to wear stage.Then,the correlation between friction,temperature and load in the process of tip sliding is studied.When the substrate is elastically deformed,the change trend of average friction is consistent with the prediction results of Hertz model.When the substrate is plastic deformed or even worn,the average friction increases with the increase of load,and the growth rate is faster and faster.Then,according to the simulation results,the excitation principle of phonons in the process of micro scale sliding friction is explained,and the resonance in the process of friction plays a key role in the excitation of phonons,providing an effective damping channel for energy dissipation.This interaction will produce excess phonons at the washboard frequency and its harmonics,resulting in the resonance of the tip.With the gradual increase of the sliding speed of the tip,multiple peaks appear in the friction curve.By adjusting the spring stiffness in the model,the position of the friction peak will also change.This means that different resonances can be controlled and generated by changing the spring stiffness.Finally,the effect of ultrasonic excitation along the Y direction on friction is discussed when the substrate is in the stage of plastic deformation.At this time,the application of lateral ultrasonic excitation can not achieve over sliding as in the elastic deformation stage,and the average friction may be reduced or increased.Then,the influence of ultrasonic excitation on the average friction is studied.When the load is low,ultrasonic excitation mainly reduces the average friction;When the load is high,the average friction will increase.In addition,after the ultrasonic excitation is applied,the resonance phenomenon in the friction process does not disappear,and the energy dissipation ability becomes stronger.The resonance can be controlled by changing the frequency and amplitude of the ultrasonic excitation.