In majority of engineering structures and mechanical components/systems, the operating load is usually varying randomly. The material property also suffers degradation with the loading conditions. This leads to continuously changing load-strength relationship and results in a variation in the failure rate. In the load amplitude domain, the situation can be described as one in which the structure or component is subjected to multiple actions of stochastic load, and the material property degrades continuously with loading pattern. Since a failure is caused when the load applied becomes higher than the relevant strength, a closed-form failure rate model is developed for a mechanical component subjected to a random load process. Consequently, the variation in failure rate is interpreted in both the load uncertainty and the component property uncertainty. Based on such a failure rate model, the effects of component strength degradation, as well as load dispersion and component strength dispersion on the failure rate are highlighted. The present paper analyzes failure rate evolvement from the competing mechanisms of statistically-increasing load and degrading strength and interprets the three stages uniformly as the manifestation of ever-changing load-strength interaction.

Received from the Guest Editor on August 25, 2009

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