Fatigue under Triaxial Stress: Development of a Testing Machine and Preliminary Results:

In this paper the reasons for attempting to investigate the effect of repeated triaxial stresses are discussed briefly. In particular the case of the thick cylinder subjected to repeated internal pressure, which is of some practical importance, is considered.The design and development of a machine capable of repeatedly applying to cylinders internal pressures of the order 20 tons per sq. in. (3,000 atm.) are described in some detail. Results are presented for such tests on one particular material and these are regarded as presenting an interim statement, but they are compared with detailed information about the properties of this material under a single and repeated application of uniaxial and biaxial stress. In all cases some attention has been paid to the effect of anisotropy.The thick cylinder tests give results much lower than might be expected from a knowledge of the properties of the material. A number of tentative explanations are put forward: some of these are at present being investigated.