Design for Reliability

Chapter 1

Design for Reliability Paradigms

Dev Raheja

Why Design for Reliability?

The science of reliability has not kept pace with user expectations. Many corporations still use MTBF (mean time between failures) as a measure of reliability, which, depending on the statistical distribution of failure data, implies acceptance of roughly 50 to 70% failures during the time indicated by the MTBF. No user today can tolerate such a high number of failures. Ideally, a user does not want any failures for the entire expected life! The life expected is determined by the life inferred by users, such as 100,000 miles or 10 years for an automobile, at least 10 years for kitchen appliances, and at least 20 years for a commercial airliner. Most commercial companies, such as automotive and medical device manufacturers, have stopped using the MTBF measure and aim at 1 to 10% failures during a self-defined time. This is still not in line with users' dreams. The real question is: Why not design for zero failures if we can increase profits and gain more market share? Zero failures implies zero mission-critical failures or zero safety-critical system failures. As a minimum, systems in which failures can lead to catastrophic consequences must be designed for zero failures. There are companies that are able to do this. Toyota, Apple, Gillette, Honda, Boeing, Johnson & Johnson, Corning, and Hewlett-Packard are a few examples.

The aim of design for reliability (DFR) is to design-out failures of critical ...