Bathtub curve

A graph showing the relationship between time and failure rate of equipment and components. Also called the failure rate curve, it is named because its shape resembles a bathtub. Immediately after the start of use, the failure rate is high due to initial failures, but it decreases over time. Then, it enters the random failure period, where the failure rate stabilizes at a low level. After the random failure period, it enters the wear-out failure period, during which failures increase due to aging and deterioration. In many cases, the service life of equipment and components is set based on the time until the wear-out failure period begins.