Realistic Fatigue Testing and Its Significance in Vehicle Component Design

Abstract

Current methods of design and development of motor vehicles tend to be limited by lack of knowledge both of the intensity of loading likely to be encountered in service and the endurance of components subjected to these loads. Conventional constant-amplitude fatigue tests are a vast simplification of the random fluctuations of stress usually found under operating conditions and predictions of service endurance based on the results of these tests will be of uncertain value until the relation between conventional tests and reality has been established.

At the Motor Industry Research Association investigations are now being made into the effects of variable load patterns on fatigue life, and the characteristics of service stresses are being determined. Because of the cost and complexity of testing full-size components, a ten-station electromagnetic fatigue machine has been developed for work on small laboratory specimens. Much of the basic information is being obtained with these specimens, and it is hoped that confirmatory tests will be carried out later on full-size components. On the ten-station machine fatigue tests have been carried out with service load patterns recorded on magnetic tape, and the results have been compared with constant-amplitude, stationary-random, and block-programme load histories. It is hoped that fatigue-test results obtained with this machine will assist in the development of realistic test procedures, and contribute to the knowledge of cumulative damage, thus shedding light on the problems of vehicle-component design.

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