Testing Methods and Techniques

Abstract

Although it is not possible to give a detailed account of the variety of equipment used to test the mechanical properties of materials at low temperatures, a brief description is given here of some of the main types of apparatus that have been employed in obtaining the results discussed in the earlier chapters. As noted in section 1.1, the uniaxial tensile test is the technique most widely used for obtaining both fundamental and design data and a large number of different tensile cryostats have been employed for this purpose.¹ Apart from the natural preference of most experimentalists to design their own equipment, there is a more fundamental reason for the development of such a variety of cryostat systems. It is, in most cases, desirable to have a machine which is as “stiff” as possible in order to observe the sharp yield and serrated stress-strain curve phenomena which were discussed in section 2.4. To achieve such stiffness, relatively massive pull-rods are needed to transmit the applied stresses, but this requirement contradicts the other basic necessity of any piece of cryogenic equipment, namely the need to minimize the heat leak into the cryogenic fluid. Thus, each design represents a compromise between these factors in addition to the usual optimization of the conflicts between initial costs and running costs, simplicity and versatility, etc.