Abstract

The recent use of rubber components in extremes of climate and under a variety of service conditions has drawn attention to the importance of the knowledge of the physical properties of rubber vulcanizates at temperatures other than normal; the dearth of such knowledge has been emphasized by the enforced replacement of natural rubber by synthetic rubbers having reduced resistance to cold. When designing mechanical parts, the engineer must know first the conditions under which the part will be required to operate and, second, the physical properties under these conditions of the materials to be used. In a recent review Riesing has given illustrations of the importance of such knowledge; in particular he has shown that rubber mountings in an automobile may well be subjected to temperatures as high as 80 to 100° C, and although rubber mountings normally warm up during their operation, they may commence to function at extremely low temperatures, while there is a limiting temperature below which they fail even to warm up. The first part of this paper gives the results of the measurement of rebound resilience on a number of vulcanizates over a wide range of temperatures. Resilience is one of the important physical properties of a rubber vulcanizate, and in designing parts for shock or energy absorption, data on the resilience of the material are essential; for such applications a material with a low resilience is required, but as the energy absorbed manifests itself in the form of heat, the temperature rise of the absorber may control the permissible value of the resilience. In many other applications it is necessary that the material should have a high resilience and so absorb little energy. The resilience is normally determined by measuring the rebound of a ball or pendulum after impact on a sample of rubber; various other methods have been used, involving, either measurement of the decay in amplitude of the damped free vibration which results when a sample is deformed and then released, or measurement of the energy loss during sustained forced vibrations. Unhappily, the results from one test do not always show great similarity to the results from another test and, as a result, the engineer has to relay on empirical correlations with resilience tests conducted in a particular way, or on service behavior. The second part of this paper gives the lines along which an investigation is being conducted to illuminate the significance of these dissimilarities. The measurement of resilience over a range of temperatures has an added importance, since it throws some light on the structure of the rubber and on the processes taking place during deformation. Recent papers which have just become available in this country show that there has been interest and activity in this field in Germany during the war years.

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