Abstract: The traditional loading-strength interference model is suitable for reliability calculation when random loading acts once or the static reliability calculation. The strength of a component is the function of magnitude and frequency of loading. The traditional loading-strength interference model cannot be used to calculate the reliability of components and system when considering strength degradation, because it assumes that loading and strength are mutually independent. The relationship between loading and strength is established through the statistic characteristics of random loading. When the loading process is Poisson process, the relationship between reliability and time and the relationship between failure rate and time are analyzed. Then the reliability models of series system and parallel system are derived. The study case shows that dispersity of original strength has an influence on reliability and failure rate of components and that relativity of loading makes the reliability of a parallel system decrease while relativity of loading makes the reliability of a series system increase.

Key words: Failure rate, Loading, Reliability, Strength, Two-dimension distribution