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Abstract-The hysteresis loss theory of rolling resistance is developed for solid rubber wheelchair tires. The analysis is used to correlate test data for a clayfilled natural rubber and a polyurethane tire material. A discussion of tire rolling work, hysteresis loss factor measurement, and rolling loss measurement is presented. An example calculation of rolling resistance for a polyurethane tire is given in detail. The subject of solid rubber tire design is developed on the basis of recommended fatigue life theory and practice. It is shown that polyurethane tires have a useful fatigue life due to a high shear modulus at useful values of hardness. This characteristic of polyurethane, if exploited, is predicted to lead to a tire with a lower rolling resistance than other wheelchair tires available. The effect of surface roughness on rolling resistance is briefly discussed and some experimental results are listed. The purpose of this paper is to give the rehabilitation engineer the means for wheelchair tire rolling resistance and fatigue life design ancl the methods to assess the tire characteristics when a tire design is modified or a new tire material is eontemplated. Other important design factors, such as wear and chemical degradation, are not discussed, but references are suggested for information on these topics. As in most research and clevelopment projects, this study raises problems which need further work. For example, the fatigue properties of the rubber compounds employed in this application are not completely understood; this subject is planned for future investigation.

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In EHL, the oil film thickness of rollers is controlled by the rate at which the oil is drawn into the conjunction of the disks by the moving surfaces of the rollers. The theory often assumes isothermal conditions in the inlet although it can be shown that the maximum shear rate often exceeds 106 sec−1, even in pure rolling. A theoretical analysis is presented for the oil temperature rise in the inlet of rollers, and the result is applied to predict the consequent film thickness. It is found that thermal effects on film thickness are only negligible at low rolling speeds. A comparison with experiment supports the conclusion that the thinning of the film thickness below that predicted by isothermal theory is substantially explained by inlet shear heating of the lubricant.

The wear performance of tribological material pairs is commonly assessed by experimental investigations which make use of rigs incorporating a pin-on-disc geometry. The information so generated is conventionally interpreted in terms of a linear relation between wear volume, applied load and sliding distance in accord with the Archard wear equation. An appropriate material parameter is thus the so-called dimensional wear rate usually measured in mm 3 =N m. However, there are many practical situations in which, as components wear, the area of apparent contact changes so that, although the Archard relation may still be applicable on the microscale, the relation between either the macroscopic wear dimension, or the total wear volume, may be other than a linear function of sliding distance or load. The following examples are considered: a spherically ended pin sliding or rotating against a flat, a pair of crossed cylinders, a radially loaded journal bearing and a radially loaded spherical bearing. Data from the wear literature are examined in the light of the analyses presented.