Abstract
This paper develops a dynamic maintenance strategy for a system subject to aging and degradation. The influence of degradation level and aging on system failure rate is modeled in an additive way. Based on the observed degradation level at the inspection, repair or replacement is carried out upon the system. Previous researches assume that repair will always lead to an improvement in the health condition of the system. However, in our study, repair reduces the system age but on the other hand, increases the degradation level. Considering the two-fold influence of maintenance actions, we perform reliability analysis on system reliability as a first step. The evolution of system reliability serves as a foundation for establishing the maintenance model. The optimal maintenance strategy is achieved by minimizing the long-run cost rate in terms of the repair cycle. At each inspection, the parameters of the degradation processes are updated with maximum a posteriori estimation when a new observation arrives. The effectiveness of the proposed model is illustrated through a case study of locomotive wheel-sets. The maintenance model considers the influence of degradation and aging on system failure and dynamically determines the optimal inspection time, which is more flexible than traditional stationary maintenance strategies and can provide better performance in the field.
Highlights
With the increasing integration of systems, maintenance strategies are placing more emphasis on techno-economic than technological considerations
We develop a dynamic maintenance model able to sequentially determine the optimal inspection time based on the system health condition and provide flexible maintenance advices
System reliability is analyzed as a first step, followed by a maintenance model evaluated based on the expected cost rate within a repair cycle
Summary
With the increasing integration of systems, maintenance strategies are placing more emphasis on techno-economic than technological considerations. In spite of the popularity of degradation models in reliability and maintenance modeling, an implicit assumption of the existing studies is that a failure occurs when the degradation level exceeds a specific threshold (soft failure). When the system is subject to continuous monitoring, maintenance actions can always be implemented before the degradation level reaches the failure threshold, and this erroneously indicates that the system will never fail. Reference [28] developed a condition-based maintenance strategy under continuous monitoring; they proposed respectively an additive and a multiplicative model to describe the relationship between system failure rate and degradation level. The maintenance strategy determines the optimal inspection time based on the updated degradation parameters and the degradation level after repair/replacement. The system is assumed to follow a stationary Gamma degradation process, which has been widely used in degradation modeling due to the property of monotonic independent increments. Where (·) is the complete gamma function, and I{x>0} is the indicator function
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