An electronic constant-stress device: its application in creep tests

Abstract
An electronic device is described which will maintain stress constant to within +or-0.1% during creep tests. The device is used in conjunction with conventional dead-load creep apparatus and, in common with all constant-stress methods, requires that the deformation of the test specimen occurs uniformly and at constant volume. The device is not strain-limited and will maintain stress constant even to the large strains characteristic of deformation in superplastic materials. Its performance compares favourably with the best cam lever machines currently available, with the advantages that the absolute value of the stress on a specimen may be calculated throughout the course of a creep test. Unlike cam lever machines, it can be used to test specimens of widely different gauge lengths with equal facility. Creep tests on 20%Cr/25%Ni/Nb-stabilised austenitic steel are described to illustrate the use of the device.

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