International Journal of Quality & Reliability Management

Purpose – The purpose of this paper is to characterise the failure model of a system that is covered by a two-dimensional warranty, one dimension depicting time and the other usage. Specifically, the authors study the effect of use-rate on system life when each constituent component life is described by an accelerated-failure-time (AFT) type model.

Design/methodology/approach – The paper evaluates the effect of use-rate on the expected failure time of a system having different internal configurations involving components. Firstly, the coherent structure as well as modules with redundant structures (standby and load-sharing) are analysed, whereby component failures are assumed to be conditionally independent. Study systems of some basic configurations with a general dependence structure among component failure instances are also studied.

Findings – The results strongly indicate that, irrespective of the internal component-configuration of the system, the models should posses the property that the expected failure time given the use-rate is a non-increasing function of use-rate. The study also reveals that dependence among components arises quite naturally due to variability in use-rate, even when all other factors of the usage environment are held constant.

Research limitations/implications – The findings of this paper are the outcome of a theoretical investigation. Although they are supported by some real-life cases as cited from the literature, it is important that they are validated through more examples.

Practical implications – The results would find a direct application in the analysis of two-dimensional warranty policies as well as the reliability assessment of consumer durables.

Originality/value – The proposed approach to the characterisation of a bivariate failure model (indexed by time and usage) is quite realistic. This investigation may lead to the development of a more suitable model.