Abstract: The time-dependent reliability model of component is developed with the order statistic and the probability differential equation. The relationship between reliability and time and the relationship between failure rate and time are studied. First, the failure mechanism of component is analyzed when random load acts for multiple times, and from the statistic meaning of random load action, the cumulative distribution function and the probability density function of equivalent load are derived with the order statistic. Further, the reliability model of component under random repeated load is built with the stress-strength interference theory. The loading process is described with the Poisson stochastic process, and the time-dependent reliability model of component without strength degeneration and the model with strength degeneration are derived respectively. The result shows that reliablity decreases with time and the failure rate also decreases with time when strength degeneration is not considered and can be neglected. When strength degeneration is obvious and is considered, reliability decreases with time more obviously and the failure rate has the whole feature of bathtub curve.

Key words: Component reliability, Failure rate, Random load, Reliability model, Time-dependent reliability