Search Results

In probabilistic reliability analysis, it is common that the models relating time to failure with environmental stresses are insensitive to the sequence of the stress level application. For a step-stress model, this means that the probability of failure is a function of the exposure time at each stress and it is unaffected by the order of stress application. These models may lead to improper reliability evaluation since it has been shown in fatigue analysis and similar areas that the stress sequencing effect may be substantial. However there is limited discussion about this topic in the reliability field. The purpose of this paper is to bridge the relationship between cumulative damage concepts in fatigue analysis and modeling and prediction of reliability. We also discuss and present reliability models and conditions where the reliability estimation model is insensitive to the sequence of the applied stresses.

Accelerated life testing (ALT) is widely used to determine the failure time distribution of a product and the associated life-stress relationship in order to predict the product's reliability under normal operating conditions. Many types of stress loadings such as constant-stress, step-stress and cyclic-stress can be utilized when conducting ALT. Extensive research has been conducted on the analysis of ALT data obtained under a specified stress loading. However, the equivalency of ALT experiments involving different stress loadings has not been investigated. In this paper, a definition is provided for the equivalency of various ALT plans involving different stress loadings. Based on this definition, general equivalent ALT plans and some special types of equivalent ALT plans are explored. For demonstration, a constant-stress ALT and a ramp-stress ALT for miniature lamps are presented and their equivalency is investigated.