Bathtub curve

A graph showing the relationship between time and failure rate of devices and components. Also called a failure rate curve, it is named so because its shape resembles a bathtub. 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, during which the failure rate remains low and stable. After the random failure period, it enters the wear-out failure period where failures increase due to aging degradation. The lifespan of devices and components is often set based on the time it takes to enter the wear-out failure period.