Tire Behavior Research Articles

Viscoelasticity and Flatspotting

Abstract Flatspotting involves delayed elasticity, so conventional principles of polymer viscoelasticity should be applicable. The strain behavior of the tire cord material during the complex stress and thermal history of the tire is idealized in a model, assuming flatspotting is caused mainly by the tire cord material and that the strains in the cord in the footprint area are less than the strains in the cords elsewhere in the tread. A flatspot index based on this model is empirically correlated with tire performance. It is shown here that this commonly used empirical index can be quantitatively interpreted in terms of a viscoelastic property of the tire cord material, in this case, creep compliance of nylon 66. Flatspotting depends on the shape of the viscoelasticity function, which is governed by chemical composition, stress differences in the tire, and the effect of environmental variables on the time scale. The most important environmental variables are temperature and moisture content. Certain qualitative predictions of tire behavior can be made on this basis.

Mechanics of the Pneumatic Tire

Abstract We have attempted to describe the mechanical problems of tires, from the point of view of elasticity theory, and have, in this connection, regarded research on the stresses and deformations in the casing as the primary problem of tire mechanics. Less attention was paid to factors which have to do with the behavior of tires with respect to the vehicle, because we believe that the effects of the choice of any design or structural parameters or materials, upon the behavior of tires, are not explainable in a sufficiently general manner, as long as the above problem, designated as the chief one, cannot be handled, at least numerically. How far we still have to go, in spite of many efforts, can be seen from Section III. The striking thing here is that belted tires have scarcely been investigated up to now. This may be due, in part, to the fact that the prerequisites for a theoretical investigation, reported in Section I, have been provided only imperfectly for this type of tire, up to now. Our own contribution, in this respect, was an outline of a generalized theory of the tire cross section, found useful for the belted tire. Measured against the state of knowledge in related fields, the present survey of the literature available to us shows that tire mechanics still represents a rather poorly developed field of research which might arouse the interest of scientists working at academic centers, for example. Section II of this work can also be thought of as stimulating interest in further development, as it mostly presents methods which can be taken over from other fields.

19. Behaviour of pneumatic tyres on wet roads : Hofferberth, W.A.T.Z., September 1965, Vol. 67, No. 9, pp. 314–320 (in German)

19. Behaviour of pneumatic tyres on wet roads : Hofferberth, W.A.T.Z., September 1965, Vol. 67, No. 9, pp. 314–320 (in German)

An Introduction to the Dynamic Properties of Vehicle Suspensions

While the general outline of vehicle suspension behaviour is fairly well known little interest has been shown in the detailed dynamic performance of the various designs. From such a study it is possible to predict the natural frequencies of the suspension systems and their response to various disturbances whether these are due to cornering forces, wind gusts or road disturbances. Initially some typical suspensions are considered using the equation of Lagrange. Body movements are considered to consist of vertical and lateral displacements together with rotation about a geometrically defined point, the instantaneous centre of roll. Wheel movements are controlled by the geometry of the particular suspension. The suspensions considered do not exhaust the subject but serve as a guide for the analysis of particular systems which may be required from time to time. The linearized equations of motion are given in matrix form, from which the natural frequencies of the system may be derived. No attempt is made to produce formulae for the natural frequencies since in practice it is more satisfactory to substitute numerical values for the symbols at this stage. Some of the differences between the tyre behaviour in static and rolling states are mentioned. This is of particular relevance in view of the development of extensive vehicle vibration test rigs.

Methods for Measuring Static Strains in Automobile Tires

Two methods for measuring strains in an automobile tire by means of x-rays are described and significant results are discussed. The first method was designed to measure tire cord strains resulting from tire ex pansion, inflation, and deflection hy studying the dimensional changes of metat-shadowed cord. The second method was developed to provide a measure of tire carcass strains by following the movement of steel balls located between fahric plies. These techniques provide means for studying cord and tire behavior during tire manufacture as well as during tire inflation and deflection. Both series of strain measurements (with shadowed cord and with steel balls) have shown quantitatively significant extensions and contractions in the cord and carcass of an automobile tire as a consequence of curing, expansion, inflation, and deflection. Specifically, it was found that after inflation nonuniform strains existed along the cords within the same ply from crown to head of a tire. Cord strains from ply to ply were also nonuniform. The cords in the crown were stretched during expansion and curing, while the cords in the sidewall were subjected to appreciable contraction ; dimen sional changes which reflected a characteristic strain pattern within the tire and which originated during expansion and curing were retained in the tire after inflation.

Construction and Behaviour Characteristics of Tyres

Development of automobile tyres over the past few years has led to certain improved performance characteristics and also to a wider choice of tyre behaviour patterns than has earlier been the case. To obtain optimum required performance characteristics for a particular vehicle design, attention must be paid both to individual tyre parameters and their interaction with particular features relating to the vehicle. Examples are given. The impact of new materials for making tyres and of constructional variations in the tyres is discussed in relation to improved tyre performance characteristics, including comfort, road adhesion, ease of control, high-speed running, tread pattern life, noise and tyre power consumption. Testing techniques which have assisted in assessment of some of these items are discussed, with illustrative results. The relative effects of mechanical and tyre variables are summarized. Reference is made to future trends in requirements of automobile tyre behaviour and possible consequent changes in tyre construction and form.

Behavior of vehicles subjected to wind gusts

This analysis gives the solution for the motion of a fourwheeled, rubber-tired road vehicle subjected to a particular type of gust load. After initially going on a straight forward driving path the car undergoes the action of a wind gust. The forces arising from this sidewise acting wind gust are applied as step functions in time. The equations of motion, in conjunction with relations expressing the tire behavior, the elastic steering system behavior and a compatibility relation for wheel contact, are derived. A perturbation procedure is applied to the governing relations and in the solutions the attention is directed to the response of the vehicle in the period of time immediately following the action of the wind gust. With the resultant solution an illustrative problem of a typical passenger car is given. The numerical results are discussed and shown graphically.

Effect of a Dynamic Fatigue Test on the Mechanical Properties of Tire Cords

Changes in the mechanical properties of cords subjected to dynamic fatigue were measured for cotton, mercerized cotton, and rayon tire cords. These data were obtained by the use of an instrument which subjected the cords under tension to localized dynamic forces under con trolled atmospheric conditions. The forces, when observed on an oscilloscope screen, were found to vary during the flex cycle. Flex life and ultimate elongation were found to be cumulative, regardless of whether the cords were fatigued continuously or were allowed to relax with or without static tension between periods of flexing. Calculated activation energies for fatigue failure were less than those for heat degradation. From the differences in properties a quali tative evaluation of tire cord behavior could be made.

Some Notes on Pneumatic Tyres

TYRES get very little attention of the inquisitive sort from those whose business it is to incorporate them in the aircraft. The only information that is usually required (and given) is the load‐deflection curve (obtained experimentally) and the overall dimensions, and that is all that is necessary for most purposes. Yet a theoretical investigation of tyre behaviour should be useful from the following aspects:

Tire Design with Relation to Comfort, Flexibility, and Wear

Abstract THIS paper summarizes some of the more important factors in tire design which exert a controlling influence on tire comfort, flexibility, and wear. It is not attempted to add to any of the fundamental principles of tire design already laid down, but it is hoped to give a somewhat clearer insight into some of the simple mechanics and economics of tire behavior. In doing so, acknowledgment should always be made of the important and fundamental work of Schippel and Healy, whose investigations have provided an exhaustive research into tire mechanics. The scope of tire design is so broad that only a very few of the most important phases of it can be treated here. Several hundred specifications enter into the construction and composition of a single tire. Furthermore, the recognized types of tire failures are very considerable in number and may be due to either chemical or mechanical defects, or both. All normal tire failures, however, can be broadly classified as carcass failures, or wear failures, the chemical difficulties being included in both groups.