Reliability Reviewed

Abstract

Using a conventional mathematical model it has been shown that a component can be designed so that it is ‘intrinsically reliable’ i.e. the failure rate will be zero for all practical purposes so long as the strength of the item remains constant. Failure can then only take place by wear-out as the strength deteriorates. Reference to field data shows that most, though by no means all, existing mechanical components conform to this pattern but fewer electronic items do. The behaviour of items which are not intrinsically reliable is shown to be substantially indeterminate and hence not amenable to assessment.

It is claimed that the concept of intrinsic reliability leads to a more rational and quantifiable approach to the best existing practice. For example, the minimum safety margin for intrinsic reliability can be calculated in terms of loading roughness. No empirical subjective factors are necessary in the design process. Leading from the concept, recommendations are made for a more logical specification of reliability and more positive methods of interpreting prototype trials. Given an intrinsically reliable design, achieving reliability in the field depends on avoiding wear-out, i.e. on the maintenance activity. Consequently the roles of the designer and maintainer can to some extent be separated, allowing a more definite allocation of responsibilities.