Finite Element Simulation of Dynamic Instabilities in Frictional Sliding Contact

This paper describes tools for numerical modeling which enable the understanding of the appearance of vibrations of a structure generated by the frictional contact between two bodies (the excitation source being friction). The dynamic finite element code PLASTD is used to reproduce transitory phenomena generated at the contact interface. This code includes contact and friction algorithms based upon a formulation which uses Lagrange multipliers. A numerical study of the dynamic response of a 2D mechanical model composed of a deformable body in relative translation and unilateral contact with Coulomb friction with a rigid surface is presented. The steady sliding solution is generically unstable and leads to a dynamic response which leads to the generation of instabilities characterized by the appearance of steady-state pulses. It is important to notice that those instabilities appear even with a constant friction coefficient of Coulomb. These simulations provided the local contact conditions (kinematics, tribological state, contact stresses, etc). The kinematics shows the existence of local impacts and sliding at high frequencies. Furthermore, local contact normal stress is found to be much higher than that expected for a smooth surface. Finally, a 3D simulation of brakes is carried out, focusing on the vibrations of the disk and the brake pad which produce noise and are due to the interface instabilities.