Papers by Francesco Massi
On the Role of Friction Vibrations for Tactile Perception of Periodic and Complex Surfaces
HAL (Le Centre pour la Communication Scientifique Directe), Oct 1, 2011
Tactile perception originates from the scanning of the fingertip on object surfaces (haptic sensi... more Tactile perception originates from the scanning of the fingertip on object surfaces (haptic sensing). Vibrations induced by the sliding contact activate the receptors (mechanoreceptors) located in the skin, allowing the brain to identify objects and perceive information about their surfaces. While the correlation between surface roughness and tactile sensation has often been investigated in literature, the spectra of the vibrations induced by the finger-surface scanning are rarely mentioned. The aim of this work is to focus on such induced vibrations, which are hold to be responsible of the tactile perception. An experimental set-up, named TRIBOTOUCH, is developed to recover the vibration dynamics by detecting the contact force and the induced vibrations at the finger nail; the test bench, based on a compliant kinematical system, has been designed and validated to guarantee the measurements of low amplitude of the vibrations of interest, and to perform measurements without introducing external noise. Experimental campaigns characterizing the vibration spectra with respect to scanning speed and surface roughness are presented and the role of fingerprints on the duplex model of tactile perception is highlighted. The spectra of the induced vibrations generated by the touching of a textile is presented and linked to the textile features
On the role of friction induced vibrations in tactile perception
Contrary to sight and hearing the tactile sense is still largely unknown. This is mainly due to t... more Contrary to sight and hearing the tactile sense is still largely unknown. This is mainly due to the lack of kowdledge on the perceived signals and to the difficulty in measuring contact forces and induced vibrations. In particular, it is known that fine texture can be appreciated only by the relative motion between the finger and the object, that gives rise to friction induced vibrations. This work focuses on the investigation of the role of these vibrations on the origin of the tactile perception and surface texture discrimination. A particular attention is placed on the effect of the different amplitude and spectral content of the induced vibrations. The results suggest the role and the limits of friction induced vibrations in the discrimination process
Experimental and numerical characterization of system response under dry frictional contact
On the role of local contact dynamics in the macroscopical frictional behaviour
This paper presents the results of a 2D non-linear finite element analysis under large transforma... more This paper presents the results of a 2D non-linear finite element analysis under large transformations of the onset and evolution of sliding between two isotropic elastic bodies separated by a frictional interface. The aim is to investigate in deep the trigger of the dynamic rupture at the interface, which preludes and goes with the sliding, and its effect on the macroscopic frictional stick-slip behaviour of the system. The analysis is focused on the energy flows associated to the interface phenomena observed during the onset of the sliding (micro-slips, precursors and macro-slips), accounting for the frictional properties and the inertial and elastic properties of the system. The results depict the frictional behaviour of a mechanical system as the outcome of a complex interaction between the local dynamics at the frictional interface and the global dynamics of the system
Proceedings of the 17th LACCEI International Multi-Conference for Engineering, Education, and Technology: “Industry, Innovation, and Infrastructure for Sustainable Cities and Communities”, 2019
Modelling of frictional contact systems with high accuracy needs the knowledge of several contact... more Modelling of frictional contact systems with high accuracy needs the knowledge of several contact parameters that are mainly related to the properties of the contact interfaces. While the interface parameters cannot be directly obtained by performing local measurements, the values estimated by means of analytical/numerical models are not reliable to describe the contact behavior, which affects in a prominent way the complex contact phenomena. This work presents a newer approach for identifying reliable values of the normal contact stiffness between rough surfaces in both sliding and sticking conditions as a function of contact pressure, surface roughness and materials. The combination of dynamic experimental tests, on a dedicated set-up, with finite element modelling allowed for an indirect determination of the normal stiffness at the contact. Keywords-contact stiffness, dynamic test, roughness, third
Tactile stimulation is used in the rehabilitation of damage to the central or peripheral nervous ... more Tactile stimulation is used in the rehabilitation of damage to the central or peripheral nervous system and in brain injury recovery. Tactile deficits of the hand are currently diagnosed through the evaluation of pain thresholds, spatial discrimination, vibration sensitivity and by using filaments or tuning forks, without truly established protocols. The global goal of the COSTaM project is to develop a tactile stimulator to identify tactile disorders and allow specific rehabilitation. The first step is to study the response of healthy individuals to complex textures in different ways: perceptive discrimination, study of friction and vibration between textures and the finger and the response of each kind of cutaneous mechanoreceptor. Three kinds of real textures have been chosen: relief, braking and fibrous. The use of a tactile stimulator, based on the modulation of the coefficient of friction with the finger, has been validated for the simulation of the braking descriptor.
Proceedings of the 17th LACCEI International Multi-Conference for Engineering, Education, and Technology: “Industry, Innovation, and Infrastructure for Sustainable Cities and Communities”, 2019
Several complex mechanisms can be responsible for undesirable friction-induced vibrations in many... more Several complex mechanisms can be responsible for undesirable friction-induced vibrations in many mechanical systems. This paper presents a tribological and dynamic analysis of the stick-slip problem, under greased lubrication, taking into account the practical application of a spring-brake system used in electric tubular motors. The main functioning of these brakes is based on the frictional greased contact between a stationary cylinder and a torsional spring, which rotates inside it. The identification of the parameters that most affect the stick-slip appearance in greased contacts requires a complete understanding and appropriate analysis of the entire system, to identify the effects of all physical parameters on the system. Here the global dynamics and the local contact behaviour is analysed, providing an in-depth examination of the stick-slip phenomenon on a greased contact. Keywords-Stick–slip, contact instabilities, tribology, greased contact, brake systems.
Lubricants, 2019
Modeling of frictional contact systems with high accuracy needs the knowledge of several contact ... more Modeling of frictional contact systems with high accuracy needs the knowledge of several contact parameters, which are mainly related to the local phenomena at the contact interfaces and affect the complex dynamics of mechanical systems in a prominent way. This work presents a newer approach for identifying reliable values of the normal contact stiffness between surfaces in contact, in both sliding and sticking conditions. The combination of experimental tests, on a dedicated set-up, with finite element modeling, allowed for an indirect determination of the normal contact stiffness. The stiffness was found to increase with increasing contact pressure and decreasing roughness, while the evolution of surface topography and third-body rheology affected the contact stiffness when sliding.
Squeaking friction phenomena in ceramic hip endoprosthesis: Modeling and experimental validation
Mechanical Systems and Signal Processing, 2015
ABSTRACT The modern evolution of ceramic bearing surfaces for total hip arthroplasty has allowed ... more ABSTRACT The modern evolution of ceramic bearing surfaces for total hip arthroplasty has allowed longer implant longevity with lower amounts of osteolysis. It has been applied to younger patient expecting improved survivorship compared with traditional bearing surfaces. However, the phenomenon of an audible squeaking produced by implants during daily activities is reported as an annoying complication for patients.
Mechanical Systems and Signal Processing, 2015
Mechanical systems present several contact surfaces between deformable bodies. The contact interf... more Mechanical systems present several contact surfaces between deformable bodies. The contact interface can be either static (joints) or in sliding (active interfaces). The sliding interfaces can have several roles and according to their application they can be developed either for maximizing the friction coefficient and the energy dissipation (e.g. brakes) or rather to allow the relative displacement at joints with a maximum efficiency. In both cases the coupling between system and local contact dynamics can bring to system dynamics instabilities (e.g. brake squeal or squeaking of hip prostheses). This results in unstable vibrations of the system, induced by the oscillation of the contact forces. In the literature, a large number of works deal with such kind of instabilities and are mainly focused on applied problems such as brake squeal noise. This paper shows a more general numerical analysis of a simple system constituted by two bodies in sliding contact: a rigid cylinder rotating inside a deformable one. The parametrical Complex Eigenvalue Analysis and the transient numerical simulations show how the friction forces can give rise to in-plane dynamic instabilities due to the interaction between two system modes, even for such a simple system characterized by one deformable body. Results from transient simulations highlight the key role of realistic values of the material damping to have convergence of the model and, consequently, reliable physical results. To this aim an experimental estimation of the material damping has been carried out. Moreover, the simplicity of the system allows for a deeper analysis of the contact instability and a balance of the energy flux among friction, system vibrations and damping. The numerical results have been validated by comparison with experimental ones, obtained by a specific test bench developed to reproduce and analyze the contact friction instabilities.
Role of damping on contact instability scenarios
In the last years, many studies have been dedicated to investigate sliding contact issues between... more In the last years, many studies have been dedicated to investigate sliding contact issues between deformable bodies. Local frictional behavior and its interaction with the global dynamics of the system has been the subject of many works in several disciplines as tribology, geophysics, vibration mechanics and fracture mechanics. Experimental and numerical papers have focused the attention on the understanding how local interface dynamics (wave and rupture propagation) affects the macroscopic frictional behavior of the system during instability regime (stick-slip instability, mode coupling instability) and conversely. The stick-slip regime is characterized by sudden friction force drops (sliding state) along the time, separated by period of elastic energy accumulation (stick state). Instead, the modal dynamic instability occurs when a vibration mode of the mechanical system becomes unstable, due to frictional contact forces. This kind of instabilities, generated by frictional forces, has been mainly object of papers [5] dealing with a specific issue named brake squeal. However general and common mechanical system can generate harmonic acoustic emission comparable to brake squeal noise during relative motion with frictional contact. In such context, the role of material damping on the frictional dynamics has been investigated by a simple frictional elastic model. Comparison between nonlinear transient simulations and complex eigenvalues analysis allowed for investigating different instability scenarios for general systems in frictional contact and drawing a qualitative map in function of damping parameters. Moreover, the results show the importance on defining a good estimation of damping to modeling system with frictional contact, in order to have reliable results. Finally a brief comparison between numerical and experimental results has been carried out
Modal dynamic instabilities generated by frictional contacts
In mechanical systems the frictional forces at the contact interfaces allow for coupling the syst... more In mechanical systems the frictional forces at the contact interfaces allow for coupling the system dynamics and the contact behavior, originating dynamic instabilities. From a numerical point of view the contact forces introduce an asymmetry on the system stiffness matrix, acting as a cross coupling factor between tangential and normal motion to the contact interface. Typical examples of this phenomenon, largely investigated in literature, are the squeal noise emission in automotive brakes or railway wheels. A general analysis is here proposed, showing how the deformation modes of a single deformable body can be excited by the frictional forces and become unstable. In this study the behaviour of a simple mechanical system is numerically analyzed. The system is composed by a polycarbonate cylinder constrained on the external surface and a steal cylinder rotating inside the first one. The inner cylinder is expanded to assure the contact pressure between the two bodies. The simplicity of the system considered allows for reducing the problem to a 2D model and the difference in stiffness between the two materials allows for considering only the polycarbonate body as deformable for the transient simulation. Two different approaches are used: a linear complex eigenvalue analysis (CEA) and a nonlinear transient analysis. The results obtained on a single deformable solid in frictional contact allow for generalizing the findings obtained in recent literature dealing with brake squeal, i.e. the lock-in instability, to a general frictional system. The selection mechanism between the unstable modes predicted by the linear CEA is investigated. An experimental validation is presented.
Dialogues numériques entre échelles tribologiques
Design and validation of an experimental set-up for the analysis of friction induced vibrations at the finger contact surface
Wave and rupture propagation at frictional bimaterial sliding interfaces: From local to global dynamics, from stick-slip to continuous sliding
Tribology International, 2012
ABSTRACT This paper presents the results obtained from a 2D non linear finite element analysis un... more ABSTRACT This paper presents the results obtained from a 2D non linear finite element analysis under large transformations of the onset and evolution of sliding between two dissimilar isotropic elastic bodies separated by a frictional interface.The aim of this work is to investigate the time evolution of the global behaviour of the system, and relating it to the local phenomena occurring at the interface. Results from the numerical parameter space study show how the system parameters affect local dynamics. Consequently, local dynamics affect the macroscopic frictional behaviour of the system and excite the system dynamic response. The evolution of the tangential force changes from stick-slip like behaviour to continuous sliding as a function of local phenomena.
Experimental Investigation and Modeling of Brake Squeal Using Simplified Test Rigs
SAE Technical Paper Series, 2007
Degradation of high loaded oscillating bearings: Numerical analysis and comparison with experimental observations
Wear, 2014
ABSTRACT Nowadays mechanical systems are expected to sustain extreme working conditions, due to t... more ABSTRACT Nowadays mechanical systems are expected to sustain extreme working conditions, due to the increase of the involved power and the optimized design. Moreover special applications like aeronautics, space engineering and robotics require the reduction of the contact area in the contact pairs, which allow the relative motion between components, by increasing the power transmitted per unit of contact area. As a consequence the joint degradations are between the main issues, resulting in possible failures or increase of consumption and maintenance costs. This paper addresses the analysis of the degradation mechanism of oscillating ball bearings subjected to high loads. These bearings, needed to assure the repetitive relative rotation between two members of the mechanical system (e.g. repetitive motions of assembling and manufacturing robots, ship helms, aircraft flaps, etc.), can reach extreme contact pressures at the ball-race contact surfaces; the oscillations of the bearings provide a fatigue loading of the contact area due to the repetitive rotation of the balls between the races. This work is aimed to calculate the contact stress distributions due to the specific boundary conditions, in order to relate them with the bearing degradation. A numerical model is presented to reproduce the loading conditions and calculate the contact stress and strain distributions in order to correlate them with the damages observed experimentally; results obtained by 2D modelling and 3D modelling, for both elastic and plastic properties of the bearing material, are reported and compared. The numerical results and the comparison with tribological observations of a degraded bearing, after cyclic load application, suggest a possible degradation scenario that brings to the failure of the bearing due to subsurface damages.
Meccanica, 2014
When dealing with complex mechanical systems, the frictional contact is at the origin of signific... more When dealing with complex mechanical systems, the frictional contact is at the origin of significant changes in their dynamic behavior. The presence of frictional contact can give rise to modecoupling instabilities that produce harmonic friction induced vibrations. Unstable vibrations can reach large amplitude that could compromise the structural and surface integrity of the system and are often associated with annoying noise emission. The study of this kind of dynamic instability has been the subject of many studies ranging from both theoretical and numerical analysis of simple lumped models to numerical and experimental investigation on real mechanical systems, such as automotive brakes, typically affected by such issue. In this paper the numerical analysis of a lumped system constituted by several degrees of freedom in frictional contact with a slider is presented, where the introduction of friction can give rise to an unstable dynamic behavior. Two different approaches are used to investigate the effects of friction forces. The first approach, the Complex Eigenvalues Analysis, allows for calculating the complex eigenvalues of the linear system that can be characterized by a positive real part (i.e. negative modal damping). The complex eigenvalues and eigenvectors of the system are investigated with respect to friction. In the second approach a non linear model has been developed accounting for the stickslip-detachment behavior at the interface to solve the time history solution and analyze the unstable vibration. The effects of boundary conditions and of system parameters are investigated. Results comparison between the two different approaches highlights how nonlinearities affect the time history solution. The lumped model allows for a detailed analysis of the energy flows between the boundary and the system during self-excited vibrations, which are at the origin of the selection between the predicted unstable mode. Keywords Frictional contact Á Mode coupling instability Á Unstable induced vibration 1 Introduction Complex mechanical systems are always subjected to vibrations induced by the frictional contacts [15, 16,
Tribology Letters, 2012
The tactile information about object surfaces is obtained through perceived contact stresses and ... more The tactile information about object surfaces is obtained through perceived contact stresses and frictioninduced vibrations generated by the relative motion between the fingertip and the touched object. The friction forces affect the skin stress-state distribution during surface scanning, while the sliding contact generates vibrations that propagate in the finger skin activating the receptors (mechanoreceptors) and allowing the brain to identify objects and perceive information about their properties. In this article, the friction coefficient between a real human finger and both rigid surfaces and fabrics is retrieved as a function of the contact parameters (load and scanning speed). Then, the analysis of the vibration spectra is carried out to investigate the features of the induced vibrations, measured on the fingernail, as a function of surface textures and contact parameters. While the friction coefficient measurements on rigid surfaces agree with empirical laws found in literature, the behaviour of the friction coefficient when touching a fabric is more complex, and is mainly the function of the textile constructional properties. Results show that frequency spectrum distribution, when touching a rigid surface, is mainly determined by the relative geometry of the two contact surfaces and by the contact parameters. On the contrary, when scanning a fabric, the structure and the deformation of the textile itself largely affect the spectrum of the induced vibration. Finally, some major features of the measured vibrations (frequency distribution and amplitude) are found to be representative of tactile perception compared to psychophysical and neurophysiologic works in literature.
Brake squeal: Linear and nonlinear numerical approaches
Mechanical Systems and Signal Processing, 2007
“Brake squeal” groups a large set of high-frequency sound emissions from brake systems. They are ... more “Brake squeal” groups a large set of high-frequency sound emissions from brake systems. They are generated during the braking phase and are characterized by a harmonic spectrum. The onset of squeal is due to an unstable behaviour occurring in linear conditions during the braking phase, and a general approach used by several authors to determine the system instabilities is the
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Papers by Francesco Massi