Rotary Power Loss Machine

Abstract

Abstract Rubberlike polymeric materials, particularly in the technical form when compounded with carbon black, are imperfectly elastic and the associated energy loss is of considerable practical significance. In some applications a high energy loss is of value to provide high damping, but in many cases and particularly in tires, the temperature rise due to the losses may be a limiting operational factor. The losses cause the tire to exhibit rolling resistance which, in the case of solid tires, can be related accurately to the modulus and resilience of the rubber. An analysis of this system has been carried out by Evans, while Tabor has considered the case of rigid cylinders and spheres rolling on flexible rubber surfaces. In the case of pneumatic tires the composite nature of the construction of fabric and rubber and the complex system of strain distribution make the calculation of rolling resistance from polymer properties extremely complicated. In order to approach this problem it is necessary to know the modulus and resilience of the materials used over a very wide range of temperature and a range of amplitude of deformation and of frequency. The required temperature range may be from −60° C to above 200° C, but the frequency range over which appreciable amplitudes are involved does not extend beyond approximately a thousand cycles per second while the amplitude of deformation does not exceed 50 per cent. In order to investigate adequately the many possible combinations of polymers and compounding systems, the values of resilience and modulus are required over the above range of conditions, and various instruments have been described which measure some or all of these properties. The rebound pendulum was one of the earliest instruments and is widely used for the measurement of resilience because of its inherent simplicity of operation and high accuracy, but as normally operated at a fixed temperature does not provide sufficient information for evaluation of materials for use in tires. This type of instrument also is not well suited for determination of modulus owing to its single cycle method of operation. The vibrator type instruments give more complete information but normally demand a high degree of skill in their operation and in the interpretation of results and are more suited to research than routine work.