Reliability: Modeling, Prediction, and Optimization

CHAPTER 15

Reliability Improvement

15.1 INTRODUCTION

As indicated in Chapter 7, the reliability of a system can be expressed in terms of the reliability of its lower-level components, down to the part level. When the reliability of the system during the design phase of the product life cycle is below the target value, it is unacceptable and must be improved. There are two basic approaches to improving system reliability, which are

1. Use of Redundancy: This involves the use of replicates rather than a single unit. The replication can be carried out at any level ranging from the system level to the part level.
2. Reliability Growth: Here the reliability of a unit (at the assembly or subassembly level) is improved through a development process that involves test–fix cycles.

In this chapter we discuss both of these approaches. The outline of the chapter is as follows. Section 15.2 deals with the use of redundancy for improving system reliability and introduces the three different types of redundancies that can be used. These are hot, cold, and warm redundancies. The next three sections, Sections 15.3–15.5, deal with each of these in more detail. Section 15.6 deals with reliability growth and the classification of the models used for assessing and predicting reliability improvement. These models can be broadly divided into two categories—discrete and continuous models. Section 15.7 discusses some of the discrete models and Section 15.8 deals with continuous models. Some comments on these ...