Practical Reliability Engineering, 5th Edition

14

Reliability Demonstration and Growth

14.1 Introduction

As described in Chapter 12, reliability testing is the cornerstone of a reliability engineering programme. Chapter 12 emphasized the importance of reliability testing being planned primarily to improve reliability by showing up potential weaknesses. However, a properly designed series of tests can also generate data that would be useful in determining if the product meets specified requirements to operate without failure during its mission life, or to achieve a specified level of reliability. Many product development programmes require a series of environmental tests to be completed to demonstrate that the reliability requirements are met by the manufacturer and then demonstrated to the customer.

Reliability demonstration testing is usually performed at the stage where hardware (and software when applicable) is available for test and is either fully functional or can perform all or most of the intended product functions. While it is desirable to be able to test a large population of units to failure in order to obtain information on a product's or design's reliability, time and resource constraints sometimes make this impossible. In cases such as these, a test can be run on a specified number of units, or for a specified amount of time, that will demonstrate that the product has met or exceeded a given reliability at a given confidence level. In the final analysis, the actual reliability of the units will of course remain ...