Comparison of two models for managing reliability growth during product design

Relying on reliability growth testing to improve system design is neither usually effective nor efficient. Instead it is important to design in reliability. This requires models to estimate reliability growth in the design that can be used to assess whether goal reliability will be achieved within the target timescale for the design process. Many models have been developed for analysis of reliability growth on test, but there has been much less attention given to reliability growth in design. This paper describes and compares two models: one motivated by the practical engineering process; the other by extending the reasoning of statistical reliability growth modelling. Both models are referenced in the recently revised edition of international standard IEC 61164. However, there has been no reported evaluation of their properties. Therefore, this paper explores the commonalities and differences between these models through an assessment of their logic and their application to an industrial example. Recommendations are given for the use of reliability growth models to aid management of the design process and to inform product development.