Reliability testing is the key to the success of a specific product design in an age when even the smallest failure in a product may lead to a massive recall, brand damage, and even safety risks. Reliability testing is a short-term test; unlike quality control, which looks at the short-term manufacturing flaws in a product, reliability testing looks at how a product degrades and fails over the long term. It provides the answers to such basic questions as ‘How long will this product last?’ In what circumstances will it be unsuccessful? What are its least strong elements? Through accelerated life testing (ALT) and highly instrumented failure analysis, engineers can squeeze years of normal operation into weeks of laboratory tests, finding ways of failure before mass production.
Fundamental Principles and Core Concepts
The concept behind reliability testing is probability theory and the physics of failure. The fundamental assumption is that the failures of products have predictable patterns, which are usually represented by such statistical distributions as the Weibull or exponential distribution. The testing is concerned with three stages of the bathtub curve: early life failures (infant mortality because of manufacturing defects), constant failure rate, and wear-out failures (degradation at the end of useful life). The important measures are MTBF (Mean Time Between Failures) in the case of repairable devices, MTTF (Mean Time To Failure) in the case of non-repairable objects, and Failure Rate.
