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Integrated Tyre and Road Interaction (ITARI)

Final Report Summary - ITARI (Integrated Tyre and Road Interaction)

The objective of the ITARI project was to provide the necessary design, test and measurement tools to investigate new road surfaces, which might lead to lower noise emission and lower fuel consumption and at the same time meeting safety requirements. In addition to this, ITARI aimed to demonstrate the implementation of virtually prototyped road surfaces in the production process of road surfaces. In this way, ITARI wishes to supply knowledge, methodology and insight to enable the research community to develop sustainable road transport for the future.

ITARI focused on the interaction between tyre / vehicle and road with its consequences with respect to:
- rolling resistance and fuel consumption;
- noise generation and radiation;
- safety;
- production techniques.

The main scientific and technical objectives of ITARI consisted of three categories: design tools, measurement methods, and demonstration of production techniques. The objective of this set of design tools was to allow for virtual design of road surfaces and their essential properties.

Based on these tools, road surfaces can be designed and implemented. To validate the tools but also to ensure that the road surfaces meet specifications defined in the design process a number of measurement tools are required. The objectives of ITARI were to suggest and demonstrate the properties of advanced road surfaces. The demonstration was scheduled to be performed by construction of test surfaces reduced to 'laboratory-scaled' test patches that are not suitable for vehicle coast-by and roll-over measurements.

While the development of models and tools took place mainly during year 1 and year 2 of the project, year 3 was specifically dedicated to the review and assessment of the project results. The main activities were demonstrating and validating the results by:
- suggesting optimised innovative road surfaces with an improved overall performance based on the models developed for the prediction of noise, rolling resistance, and wet grip;
- building such virtually designed surfaces applying new and innovative pavement technology;
- validating the results by measurements.

One main outcome of the project was a database of road surface data and coast-by level spectra for 840 different tyre pavement combinations. These were specifically treated dense and porous pavements, driven over at rolling speeds from 50 km/h up to 120 km/h. The parameters of texture and acoustical impedance of the road surface have been varied in a systematic way. The tyre set comprised of 16 different types of passenger car tyres and 4 types of truck tyres including a subset of slick tyres. Results of near field measurements of the rolling noise of two sets of normal car tyres on the 42 different road surfaces completed the measurements. The data are unique due to thoroughly adjusted and controlled boundary conditions to ensure that the data were free from the corrupting effects of varying tyre temperature and inflation pressures etc. From the data it was possible to identify surface textures, which might give much lower tyre / road noise generation than is known from conventional pavements.

Inside vehicle industry even simpler methods are applied for estimation of the contribution of the rolling resistance to the total fuel consumption. These models are not suitable to study the influence of road design parameters. In the tyre industry, finite element models are used to calculate the deformation and energy losses during rolling. However, the models are not able to calculate the dynamic contact and are, therefore, not be able to describe the variation of energy losses during rolling as function of different road surfaces. Consequently, to the best of the research groups' knowledge, there are no studies in the open scientific literature, or in industry, modelling the influence of road surface properties on rolling resistance. One of ITARI's objectives was the development of such models. These models to be developed are based on the formulations for tyre vibration and dynamic tyre-road contact force in RATIN, which will be further enhanced for rolling resistance prediction, thereby facilitating a sustainable transport system.

The frictional behaviour of rubber, unlike friction of other solids, is controlled by the very low elastic modulus giving high internal energy losses over a wide frequency band. The friction force is mainly derived from the loss modulus, a bulk property of the rubber. For tyre / road contact, two contributions of rubber friction become important, commonly described as the adhesion and hysteretic components, respectively. Although pavement texture has been considered in tyre/road contact modelling within the last years this has been done in a more general, empirical way and, besides that, focussed on tyre / vehicle behaviour. To use friction modelling in designing the grip properties of pavement surfaces is a new approach adopted by this project.

There are three properties that characterize the road surface in terms of tyre / road noise, grip and rolling resistance: texture, porosity and flexibility. In order to make road surfaces safe and durable, mixtures of mineral aggregates and powerful binders are used for the construction in the present situation. For safety reasons, the surface of a road must show a certain roughness combined with certain microscopic properties. The basic idea of this project was that the pavement characteristics can be optimised with respect to the tyre-road interactions: noise, rolling resistance and grip. When the physical processes that lead to these effects are understood mathematical models and consequently design tools can be developed that can help to make better pavements.

The first attempts with the hybrid model within the Sperenberg project has shown that there are new, not yet applied textures and road constructions, which are likely to lead to very effective, noise reducing road pavements. The noise reduction potential is expected to be 6 dB for passenger car tyres on dense road surfaces (referenced to stone mastic asphalt 0/8 or 0/11). Combining these low noise textures with sound absorbing and / or flexible constructions should add at least 4 or 5 more decibels - independently from the tyre and the speed. However, the effects on grip, (durability) and rolling resistance are not yet known. To implement this noise reduction potential on real road surfaces investigations on new materials and construction methods are necessary which are able to produce textures, void structures and flexibility in a well directed and reproducible way - not neglecting the crucial properties grip, (durability) and rolling resistance. The problem of conforming to conventional road construction procedures has to be overcome. However, development of new types of road surfaces by means of measurement procedures and calculation models for analysis and synthesis will help to improve the state of the art.