Evaluation of the Physical Properties of Rubber Vulcanizates at Low Temperatures

The technical importance of rubber vulcanizates in fields where they are likely to be subjected to temperatures lower than normal requires no emphasis, and has resulted in considerable activity being directed to the evaluation of the physical properties of rubber vulcanizates at such temperatures. The purpose of these investigations has been to compare the low temperature serviceability of various rubbers, and to study of the behavior of the materials at these temperatures in order that the data obtained may be used to assist design. Such extension of knowledge is of great importance since rubber vulcanizates exhibit considerably increased stiffness and become brittle at low temperatures. Several good summaries of the work exist in the literature; these show that there is a considerable lack of uniformity in the methods of testing and representation. As a result of this wide diversity of test methods, there is no generally accepted index of low-temperature serviceability. Many of the tests which have been used involve the extension of the usual technical tests to lower temperatures, whereas others involve a study of the performance of rubber components in conditions of service. The results of such tests generally have been quoted as a temperature below which a particular property fails to fulfil a given requirement. The endeavor to obtain one temperature or one parameter which characterizes the resistance to low temperatures has been only partially successful, since the interdependence of stress, strain, time and temperature make it impossible to formulate relations of a simple character which describe the behavior of rubber vulcanizates over even a limited range of conditions. First, there is the need for an accepted standard test (or tests) ; secondly there is the need for a convenient method of expressing the resistance to low temperatures, and lastly, there is the need for the development of the ideas of the processes leading to the changes in physical properties at low temperatures. In this paper it is intended to review the various methods which have been suggested for low-temperature testing, to indicate the sources of the inadequacy of the individual tests, and to describe the initial results of an investigation, as yet incomplete, into a convenient means of testing and representing the mechanical properties at low temperatures.