The aim of this chapter is to provide an understanding of reliability modelling as it applies to the modelling process. It is not the intention to give exhaustive descriptions of the more sophisticated modelling techniques that may be obtained from the references and other literature. Its intent is rather to describe the more common techniques that may be used and essential features that must be taken into account.

The purpose of reliability modelling is to generate a mathematical picture of a system in the environment in which the system is to be used. It is important, before modelling begins, that both the system and the environment in which it is to be operated are understood. The consequences of system failure and the ability to repair the system should also be considered.

In particular, it should be noted that in this chapter, little consideration is given to the modelling of systems in which redundant sub-systems are repaired prior to system failure. In other words, each component or non-redundant sub-system is assumed to have an infinite repair time (zero repair rate). Thus, when such a component or sub-system fails, it remains in this state until the system of which it is a part is completely repaired or replaced in its entirety. In effect, this form of maintenance strategy typifies one-shot devices such as fire extinguishers, undersea cables, weapons systems and the like. For a brief summary of procedures to be adopted for modelling systems in which redundant sub-systems are repaired prior to system failure, see Reliability Evaluation when Redundant Sub-systems can be Repaired Before System Failure.

This chapter develops the principles outlined in Reliability Prediction Methods”], and describes:

The methods described in this chapter can be applied generally to most types of equipment (bearing in mind the comments made in the introductory paragraphs). However, Guided Weapon System (GWS) example is used to illustrate these methods because such systems often consist of a variety of equipment, each with differing operating and maintenance conditions.