Research On Reliability Modeling And Condition-based Maintenance Strategy Of The Two-phase Degradation System

Accurate reliability assessment and reasonable maintenance strategies can effectively prevent system failures and save maintenance resources,thereby being of vital importance for ensuring reliability,safety and economy of systems.In engineering practice,due to the stochastic inner deteriorating mechanism or dynamic operating environment,the degradation rates of some systems change significantly at some moment(the moment is called the degraded change-point),so that the degradation processes of such systems exhibit two-phase degradation characteristics.Unknown time and its degradation state of the degraded change-point make reliability-related studies more challenging.Thus,in this dissertation,reliability modeling and conditionbased maintenance strategy for the two-phase degradation system with a degraded change-point have been studied.Firstly,Wiener stochastic process is applied to model the two-phase degradation performances,where random effect parameters are introduced to capture unit-to-unit heterogeneity of the degradation rates and the degraded change-point.According to Bayesian theory,offline parameters estimation is based on prior information such as experts experience and historical degradation data from individuals in the same population,and by combining online real-time degradation data of the operating system,online parameters updating is implemented.The analytical expressions of the parameters joint posterior distributions are then derived.Afterwards through the failuretime distribution of Wiener process at the first passage time,the reliability functions and the remaining useful lifetime functions based on two-phase degradation modeling are analyzed.The case study of liquid coupler devices shows that the proposed method can effectively reflect the degradation characteristics of the operating system,and that with online real-time degradation data accumulating,deviations of reliability estimated results and remaining useful lifetime predicted results are both reduced.Finally,a condition-based maintenance strategy under perfect maintenance is proposed.Considering minimizing the average long-run cost rate as the optimization criterion,a maintenance decision-making model with the pre-maintenance threshold and the periodic inspection interval as decision variables is constructed and optimized.Based on two-phase Wiener degradation processes,we derive the analytical expression of the average long-run cost rate and obtain the optimal maintenance strategy through simulation and numerical search.