Coupling system dynamics and local contact behaviour

Actual mechanical systems include surfaces in sliding contact that are subjected to wear if exposed to large vibration. In fact, the vibration of components in contact results in large oscillations of the local contact stresses, due to the local deformation of the components at the contact interfaces. Vice-versa the local contact behaviour affects largely the system dynamics. An interdisciplinary approach is need to handle dynamic and tribological problems.

Fingers are moved to scan the object surfaces generating skin vibrations. The information on object surfaces is contained in the friction induced vibrations. The mechanoreceptors, mechanical sensors immersed into the skin, have the key role of transducing the stress state oscillations into electrical impulses conveyed to the brain. It is needed to develop appropriate investigations to link the vibration spectra generated by the finger scanning with the tactile sense.

 
Wave propagation at  contact interfaces

Friction is a stiff phenomenon, depending on several parameters and affecting system behavior. At the frictional contact the relative motion gives rise to local ruptures and waves which propagate at the interface. An understanding of wave propagation and generation at the contact is fundamental for understanding friction induced vibrations and the macroscopic frictional behaviors (local and macroscopic stick-slip, continuous sliding, ...) at the origin of several phenomena such as earthquakes or surface machining damages.

 
Maps of contact instability scenarios

Phenomena rising when two body are in frictional contact like stick-slip, fatigue failures, self-excited vibrations, are substantial subject of interest in different domains, such as nonlinear dynamics, tribology, biomechanics, or geophysics. The aim of this project is to investigate the instability scenarios occurring when friction forces excite the mechanical systems during the relative motion; the coupling between the frictional behaviour at the contact and the global dynamic of the system bring to either stick-slip phenomena, or modal instabilities.

 
Hip endoprosthesis Squeaking noise emission

The ceramic-on-ceramic bearings are characterized by low wear rates and an excellent biocompatibility. Nevertheless, recent worrisome rates of squeaking noise occurrence are reported for this kind of prosthesis. The aim of this project is the development and validation of a numerical model able to predict the friction induced vibrations at the origin of the squeaking noise emission. The model allows as well for recovering the same in-vivo squeaking frequencies and for comparing squeaking propensity of different prosthesis designs.

 
Energy transfer between acoustic fields by frictional contacts for passive structural monitoring

The friction nonlinearity between sliding surfaces can be used to transfer vibrational energy between acoustic fields, by the dynamic response of the solids in contact. The energy transfer can be useful for several applications such as passive health monitoring and diagnostic, recovering of environmental vibrational energy, etc. Numerical and experimental analyses are used to develop a mechanical system able to transfer energy between the wished acoustic fields.

 
Analysis of degradation scenarios of high loaded oscillating bearings

This project addresses the analysis of the degradation mechanism of oscillating ball bearings subjected to high loads. These bearings can reach extreme contact pressures at the ball-race contact surfaces; the oscillation of the bearings provides fatigue loading of the contact area due to the repetitive rotation of the balls between the races. A numerical plastic model with contact nonlinearities and experimental tribological observations are developed to highlight the degradation scenarios and to prevent/predict the bearing failure.

 
False Brinelling degradation of bearings exposed to vibrational environment

This project deals with the numerical analysis aimed to reproduce the behavior of the local contact stresses between balls and raceways of the rolling bearings used into bleed valves of aircrafts. The scenario of the false Brinelling degradation of the race surfaces is investigated. A multi-body nonlinear model is developed to account for the vibrational excitation from the engines and the dynamic response of the bleed valve. The forces acting on the bearings are then introduced in a finite element model by the code PLASD2, in order to recover the stress distribution at the contact. The stress values at the nucleation zones of the false Brinelling degradation are recovered numerically.

Energy balance of a frictional contact: contact damping and friction induced vibrations

One of the research branches the most investigated lies in the field of non-linear dynamics and deals with the vibration damping by frictional contact. A more general approach accounting for the energy transfer between surface and solid dynamics is needed to identify the energy effectively dissipated at the contact and the energy reintroduced in the system by friction induced vibrations. To allow this distinction, a main attention is addressed to the energy balance and a correct analysis of the energy flows. energy, etc.

Coupling mechanism, first bodies and third body scales of the tribological triplet

The tribological triplet (mechanism, first bodies, third body) is the framework of every contact issue. Different spatial and time scales intervene in the phenomenon. While several numerical methods deal with the different scales separately, a global approach is still unknown. The project aims to propose a coupling of numercal methods (FEM, DEM, ...) dealing with the different scales, for a more accurate modeling of contact issues.