bath-tub curve

= failure-rate curve

A graph, having the outline shape of a bath tub, in which the failure rate of a piece of machinery is plotted against time (on the horizontal axis). The graph has three phases: a burn-in or start-up phase, during which faults related to installation and assembly are likely to show up quickly; a normal phase, during which the machine will be reliable as long as it is maintained and used within its design parameters; and a wear-out phase, during which the machinery reaches the end of its design life and parts begin to fail at a rate that makes it uneconomical to repair. The extent of each phase will vary, e. g. a piece of electronic equipment might function perfectly until the moment that it fails. In practical terms, it has no wear-out phase.