International audienceThis 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
International audienceThe aim of this paper is to present a means of analysing "friction instabilities". The explicit dynamic finite element software PLAST3 in 3D is used to simulate the behaviour of the two bodies (pin and disk) of a tribometer during frictional contact. Coulomb's friction law is used at the contact surface. The phenomenon of relay between the instantaneous contact zone, the contact stresses distribution and the kinematics of the contact surfaces are presented. As the friction coefficient and velocity of the disk are considered constants in the simulations, the contact zone (stick, slip) and separation depend on a "dynamic effect". This generates wave propagation in the interface and involves a variation of normal contact stress. Definitions of macroscopic and local friction coefficients are given. The interfacial instabilities due to the dynamic effect produce a macroscopic friction coefficient that is less than the local friction coefficient. The influence of disk velocity on the macroscopic friction coefficient is also investigated
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