Considering Prior Information for Accelerated Tests with a Lifetime-Ratio

The higher the reliability requirements on a product are, the more extensive the test must be to ensure the required reliability. One is often unable to obtain a reasonable amount of test items, when stresses approximate normal operating conditions. To reduce sample-sizes and test duration components are exposed to much higher stresses during the test than within their normal use conditions. Therefore, it has to be ensured that the failure mechanism of the component operating under higher stress is identical to the failure mechanism under normal stress. Then, the failure behaviour under normal operating conditions can be predicted if the value of the acceleration factor is known. The so-called lifetime-ratio considers a case where the test time is not equal to the required product lifetime. Furthermore, there exist different Bayesian methods to reduce the test effort. In this paper the acceleration factor is added to the methods by Kleyner et al. and Beyer/Lauster. Furthermore, the lifetime-ratio is added to the method by Kleyner et al.. The methods are compared and discussed within a practical example where the required reliability for a mechanical component has to be ensured. 1. Acceleration Factor and Lifetime-Ratio For the prediction of the component failure behaviour under normal operating conditions it is necessary to know the value of the acceleration factor. The acceleration factor shows how high the lifetime ts of a component is under normal operating conditions in relation to the component lifetime tt under highly stressed conditions. The acceleration factor is given by (Tobias 1998)