Measuring reliability during product development considering aleatory and epistemic uncertainty

Traditionally, reliability engineers use probabilistic reliability metrics (e.g., the probability of failures) to measure a product´s reliability. In the product development phase, the probabilistic reliability metrics are predicted by developing physics-of-failure-based (PoF-based) models to calculate the time-to-failure (TTF) and propagating the uncertainty in the model parameters. The prediction method only considers aleatory uncertainty (the variability of the parameters). In real cases, however, products are also exposed to epistemic uncertainty, which is the result of our incomplete knowledge of failures. In order to measure reliability in presence of both aleatory and epistemic uncertainty, belief reliability, a new reliability metric is defined in this paper and an evaluation method for the belief reliability is proposed. Epistemic uncertainty is incorporated in the evaluation by assessing the performances of the reliability techniques implemented in the product development phase. The applications of the metric and the evaluation method are illustrated through an example. The result indicates that the probabilistic reliability metrics ignore the epistemic uncertainty and overestimate the reliability. Thus, belief reliability is a more appropriate reliability metric for the product development phase.