A method to model component reliability is presented, where the life is measured by the number of load applications. With static strength failure and fatigue failure as the scenario, the dynamic models for calculating the reliability and failure rate of components under random repeated loads both without strength degradation and those with strength degradation are derived. The relationship between reliability and the number of load applications, and that between failure rate and the number of load applications are discussed in different cases. The result shows that both the reliability and the failure rate of components decrease as the number of load applications increases. This is even though the strength does not degenerate, and the failure rate curve has the partial characteristics of a bathtub curve, with an early failure period and a random failure period. When strength degenerates with the number of load applications, the reliability of components decreases more obviously, and the failure rate curve of components is bathtub-shaped.

Received on July 10, 2009, revised on September 2, 2009

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