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The results of an experimental activity carried out with the aim to investigate on the adhesive behaviour of visco-elastic materials in sliding contact with road asperities are presented. Experiments are carried out using a prototype of pin on disk machine in which pin is constituted by a specimen of rubber coming from a commercial tire, while diff...
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... With the aim to reproduce the functionalities between adhesive friction and the main variables influencing it (i.e. sliding velocity V s , contact pressure p and temperature T), a model, which takes into account both the approach of Le Gal and Klüppel [16] and the one of Momozono and Nakamura [17], has been adopted: (8) in which, from Le Gal's model, (9) and, from Momozono's model, the ratio of the real actual contact area A c to the apparent contact area A 0 is approximated by: (10) Thanks to a wide experimental campaign, performed by the authors using a pin on disk machine [18] [19], it has been possible to identify the parameters of Le Gal's model most difficult to define, i.e. the interfacial shear strength τ s,0 , the critical velocity v c and the viscoelastic dissipation parameter n. ...
The aim of the paper is the study of the frictional behaviour of a tyre tread elementary volume in sliding contact with road asperities. Friction is supposed as composed by two main components: adhesion and deforming hysteresis. The target, fixed in collaboration with a motorsport racing team and with a tyre manufacturing company, is to provide an estimation of local grip for on-line analyses and real time simulations and to evaluate and predict adhesive and hysteretic frictional contributions arising at the interface between tyre tread and road.
A way to approximate asperities, based on rugosimetric analyses on macro and micro scale, has been introduced. The adhesive component of friction has been estimated by means of a new approach based on two different models found in literature, whose parameters have been identified thanks to a wide experimental campaign previously carried out.
The hysteretic component of friction has been estimated by means of an energy balance taking into account rubber viscoelastic behaviour and internal stress / strain distribution, due to indentation with road. The correct reproduction of friction phenomenology and the model prediction capabilities are highlighted making particular reference to grip variability, due to changes in working conditions.
... Through the wheels, the vehicle exchanges forces with the track [12][21] which depend on the structure of the tyres [35] and on their adherence, strongly influenced by temperature [36] [37]. Theoretical and experimental studies, aimed to predict temperature distribution in steady state pure rolling conditions, useful to evaluate its effects on energetic dissipation phenomena, are quite diffused in literature [38] [39]. ...
... Thanks to the experimental campaign illustrated in the previous paragraphs, performed using a pin on disk machine and discussed also in [36] [37], it has been possible to identify the parameters of Le Gal's model most difficult to define, i.e. the interfacial shear strength τs,0, the critical velocity vc and the viscoelastic dissipation parameter n. ...
The target of the activities described in the PhD thesis, fixed in collaboration with a motorsport racing team, with a high performance vehicle manufacturing company and with a tyre research and development technical centre is the development of a procedure able to estimate tyre interaction characteristics, reproducing them in simulation environments taking into account the fundamental friction and thermal phenomena concerning with tyre/road interaction.
A first tool, called TRICK, has been developed with the aim to process data acquired from experimental test sessions, estimating tyre interaction forces and slip indices. Once characterized the vehicle, filtering and sensors output correction techniques have been employed on the available data, creating a robust procedure able to generate as an output a "virtual telemetry" and, following a specifically defined track driving routine, to provide tyre interaction experimental curves.
TRICK virtual telemetry can be employed as an input for the second tool, TRIP-ID, developed with the aim to identify the parameters of a Pacejka Magic Formula tyre model. The advantage of this kind of procedure is the possibility to simulate the behaviour of a tyre without the bench characterizations provided by tyremakers, with the further benefit to reproduce the real interactions with road and the phenomena involved with it, commonly neglected in bench data.
Among such phenomena, one of the most important is surely the effect that temperature induces on tyre performances, especially in racing applications. For this reason a specific model, called TRT, has been realized and characterized by means of proper thermodynamic tests, becoming a fundamental instrument for the simulation of a tyre behaviour as close to reality as possible. One of the most useful features provided by the model is the prediction of the so called "bulk temperature", recognized as directly linked with the tyre frictional performances.
With the aim to analyse and understand the complex phenomena concerning with local contact between viscoelastic materials and rough surfaces, GrETA grip model has been developed. The main advantage to which the employment of the grip model conducts is constituted by the possibility to predict the variations induced by different tread compounds or soils on vehicle dynamics, leading to the definition of a setup able to optimise performances as a function of tyre the working conditions.
The described models and procedures can cooperate, generating a many-sided and powerful instrument of analysis and simulation; the main features of the available employment solutions can be summarised as follows:
full geometric, thermodynamic, viscoelastic and structural characterization of tyres on which the analyses are focused;
estimation of the tyre interaction characteristic curves from experimental outdoor test data;
definition of a standard track driving procedure that employs tyres in multiple dynamic and thermal conditions;
identification of Pacejka Magic Formula tyre models parameters on the basis of the estimated tyre interaction characteristic curves;
estimation of surface, bulk and inner liner tyre temperatures for variable working conditions and real-time reproduction of tyre thermodynamic behaviour in simulation applications;
correlation of tyre thermal conditions with friction phenomena observable at the interface with road;
prediction of tyre frictional behaviour at tread compound and soil roughness variations;
modelling of tyre interaction by means of MF innovative formulations able to take into account grip and thermodynamic effects on vehicle dynamics;
definition of the optimal wheels and vehicle setup in order to provide the maximum possible performances improvement.
... applied load, surface roughness and rubber characteristics) is plotted as a function of V s in order to highlight the good agreement with the experimental results. 32,33 As stated above, the differences between the dry and the wet experimental results can be attributed to the substantial reduction in the adhesive component of friction in wet conditions. Further experimental studies will concern the investigation of the hysteretic component of friction in the interaction with surfaces characterized by a lower roughness. ...
This paper deals with the frictional behaviour of a tyre tread elementary volume in sliding contact with road asperities. Friction is supposed as composed by two main components: adhesion and deforming hysteresis. The target, fixed in collaboration with a motorsport racing team and with a tyre manufacturing company, is to provide an estimation of local grip for on-line analyses and real time simulations and to evaluate and predict adhesive and hysteretic frictional contributions arising at the interface between tyre tread and road. A way to approximate asperities, based on rugosimetric analyses on macro and micro scale, has been introduced. The adhesive component of friction has been estimated by means of a new approach based on two different models found in literature, whose parameters have been identified thanks to a wide experimental campaign previously carried out. The hysteretic component of friction has been estimated by means of an energy balance taking into account rubber viscoelastic behaviour, characterized by means of proper DMA tests, and internal stress / strain distribution due to indentation with road. Model results are finally shown and discussed and the validation experimental procedure is described. The correct reproduction of friction phenomenology and the model prediction capabilities are highlighted making particular reference to grip variability due to changes in working conditions.
... Through the wheels, the vehicle exchanges forces with the track [1,2] which depend on the structure of the tyres [3] and on their adherence, strongly influenced by temperature [4,5]. ...
In the paper a new physical tyre thermal model is presented. The model, called Thermo Racing Tyre (TRT) was developed in collaboration between the Department of Industrial Engineering of the University of Naples Federico II and a top ranking motorsport team.
The model is three-dimensional and takes into account all the heat flows and the generative terms occurring in a tyre. The cooling to the track and to external air and the heat flows inside the system are modelled.
Regarding the generative terms, in addition to the friction energy developed in the contact patch, the strain
energy loss is evaluated. The model inputs come out from telemetry data, while its thermodynamic parameters come either from literature or from dedicated experimental tests.
The model gives in output the temperature circumferential distribution in the different tyre layers (surface,
bulk, inner liner), as well as all the heat flows.
These information have been used also in interaction models in order to estimate local grip value.
... The essential relationship between adhesive and hysteretic friction is taken into account by means of Kuznetsov's parameter K, that is supposed to be equal to the adhesive friction coefficient. Thanks to a wide experimental campaign, performed by the authors of the present paper with the aim to investigate tyre/road adhesive component of friction arising in the sliding contact with micro-rough profiles [22, 23], it has been possible to identify the optimal value of K for each kind of analysis. Applying Kuznetsov equations in the x-z plane, it is possible to calculate the stress components σ x and σ z generated by the sliding indenter in the direction of sliding velocity. ...
Knowledge about phenomena concerning with adherence is a key factor in the automotive field and in particular in the braking/traction and stability control systems design. Moreover, the continuous drivers’ seeking of the optimal grip conditions, makes the development of a physical friction model an essential instrument for the investigation of the factors acting on indentation and adhesion mechanisms on which tyre/road interaction is based. Rubber/asphalt friction, in fact, is influenced by a great number of variables and parameters, often hard to be controlled and measured: macro and micro roughness of the bodies in contact, pressure arising at their interface, materials stiffness characteristics and their frequency and temperature dependence, relative motion direction and speed.
The possibility offered by a physical model to provide a better comprehension of the cited factors allows to act on them with a wide range of aims: studying soil textures structured in order to increase drivers' safety both in dry and in wet conditions,
producing more performing rubber compounds, able to optimize frictional behaviour under certain temperatures or frequencies and, in particular in race applications - for which the presented studies have been originally carried out - in order to configure optimal vehicle setup and driving strategies.
A deep knowledge of the mechanisms involved with tyre/road friction is a key factor in the design of the suspension system: an optimal setting of tyre working angles, operated in order to optimize temperature, contact pressure and sliding velocity distributions, can be efficiently provided by a physical grip model able to indicate the best wheel configuration at the boundary conditions changes.
... Thanks to a wide experimental campaign, performed by the authors of the present paper with the aim to investigate tyre/road adhesive component of friction arising in the sliding contact with micro-rough profiles [28], [29], it has been possible to identify the optimal value of K for each kind of analysis. ...
According to the most recent approaches, the friction coefficient arising between tyre rubber and road can be seen as constituted by three components: adhesion, deforming hysteresis and wear.
This paper deals with the estimation of the hysteretic component of friction. This component is due to indentation phenomena regarding contact mechanics of deformable bodies sliding on the asperities of a rough substrate, which exert oscillating forces at the interface, leading to cyclic deformations of the rubber and then to energy "dissipation" via its internal damping. To evaluate this component, a physical model able to calculate energy dissipation of a rubber block indented by a rigid asperity in sliding contact has been built. To this aim the visco-elastic characteristics of the material have been taken into account.
The road profile has been modelled as the sum of two sinusoidal waves characterizing the macro and the micro roughness scales.
The results coming out from the physical model have been validated by means both of FEM models results and of experimental tests carried on a pin on disk tribometer.
