Friction-Induced Vibrations as a result of system response and contact dynamics: a newer friction law for broadband contact excitation

Friction-Induced Vibrations (FIV) are a complex phenomenon which arises each time two surfaces undergo relative sliding. During the last decades, a significant amount of experimental and numerical works dealt with Friction-Induced Vibrations, while the simulation of the dynamic excitation from frictional contacts has always been a real challenge to face in many industrial research areas. In this research framework, this work is addressed to the investigation of the Friction-Induced Vibrations, carrying on at the same time experimental and numerical analyses; a new numerical approach is proposed to reproduce the local dynamic excitation from the contact and its effect on the vibrational response of the system, without significant increase of the computational time costs. The mechanical system, object of the investigation, is composed by two steel beams in frictional contact during relative motion; the simple dynamics of the system allows for distinguishing between the dynamics response of the system and the broadband excitation coming from the contact. A parametrical experimental campaign has been conducted to analyse the effects of three main contact parameters (the relative sliding velocity, the normal load and the surface roughness) on the system vibrational response, i.e. on the induced vibrations. In parallel, a numerical model has been implemented to reproduce the local dynamic excitation from the contact and its effect on the vibrational response of the system. A new friction law has been introduced in the model, proposing the use of a perturbative term in the friction coefficient in order to simulate the effects of the contact excitation. The inclusions of the local dynamic excitation, due to the contact phenomena, by the perturbation term of the friction coefficient allows to correctly reproduce the Friction-Induced Vibrations without introducing a representation of the real surface topography, which usually needs a large number of elements, saving then computational time. Different signals for the perturbative term have been tested to simulate correctly the measured vibrations. The evolution of the perturbative term recovered by an inverse method allowed for highlighting the different spectral contributions of the local excitation coming from the contact. The comparison between the measured Friction-Induced Vibrations and the ones simulated numerically showed good correlation, validating the proposed friction law. Finally, the effect in a change of the sliding velocity and surface roughness have been simulated numerically too and correlated with experimental results.