Reliability Prediction Methods
Introduction
Reliability prediction depends essentially upon producing a model that represents the reliability relationships between items comprising a system (which is further described in Reliability Modelling, and then evaluating the various elements within the model to provide a quantitative estimate of the system reliability and its constituent parts. This chapter describes methods that may be used to evaluate reliability at different stages of a project, depending upon the data available at the particular time. Frequent reference is made to the failure rate models described in Reliability Modelling.
The methods that can be used during a project fall into two main categories as follows:
• Those which make use of previous experience, design data and standard failure rate data to give theoretical predictions of the reliability that a design may achieve when it reaches maturity (e.g., after being in service for two to three years). Such methods can be used before any hardware is produced. They include the Similar Equipment, Generic Parts Count, Parts Stress Analysis and Missile Prediction methods. These methods are described in subsequent paragraphs.
• Those which make use of the results of hardware testing to give practical estimates of the reliability that a design is achieving during development and predictions of probable achievement in the future. Methods of testing and mathematical techniques and models for analysing test results are described fully in
Bibliography, and are not considered further in this guide.