Reliability And Maintenance Research For Competing Failure System With Degradation Process And Shock Process

The reliability research,which came from 1950 s,makes great contributions to improve the quality of products,enhances product safety and promotes the beneficial efficiency in enterprises.With the development of modern science and technology,the quality of the products continuously improve,many products cannot be collected the enough failure data in short time,even none failure data,and it is a great challenge to the traditional reliability research,which is based on the failure data.Reliability modeling and analysis based on performance degradation,which depend on the performance degradation data in different time,its greatest advantage is that the reliability research based on the products failure mechanism,while not required the failure data.The reliability research based on performance degradation has made great progress,which is one of the key technologies to solve the reliability design,analysis,test and assessment of the high reliability and long lifetime products;it received good economic benefits and remarkable social benefits.For the complexity of the product operation circumstance,products are often suffered inner or external shocks.Different shocks may results different effects,some shocks will accelerate the performance degradation process,others shocks even lead to products failure immediately.Many products are suffered both performance degradation processes and random shocks processes,and there are some research results of reliability on this case.However,most existing studies of reliability modeling based on competing failures of degradation process and random shock process take aim at some particular cases.A systematic study of the theory and methods has not been found,which is an obstacle of its further application and development in reliability model.Hence,this thesis focuses on dealing with various problems encountered in reliability modeling and analysis based on competing failures of degradation process and random shock process in such aspects as reliability model,parameters estimation,reliability assessment and preventive maintenance.The main contents and achievements of this dissertation are summarized as follows:(1)For complex systems or items that experience multiple dependent competing failure processes,the dependency among the failure processes presents challenging issues in reliability modeling.We discuss the dependence of the degradation failure processes and the traumatic failure process.On the condition of shock processes,a degradation failure reliability model is developed with the wiener degradation processes.By the influence of the degradation,a traumatic failure reliability model is developed under weibull failure distribution.Then,we get system reliability model deals with mutual effect of the two processes.In additional,the parameters estimation of the reliability model is solved.An applied example demonstrated the model correctness andavailability the parameters estimation of the reliability are discussed.(2)we assume that the product in the burn-in procedure only experiences continuous smooth degradation process,while in the field operation period the product experiences both continuous smooth degradation process and shock process.The shock process can cause the product not only traumatic failure,but also additional abrupt degradation damage.After the system reliability model and maintenance model have been proposed,the optimal burn-in setting and age replacement duration are obtained under the considering of minimizing the long run average cost rate.A numerical example with the real data is analyzed to illustrate the application of the model.(3)Degradation and shock are two common mechanisms accounting for system failure.We assume that the system experiences both continuous smooth degradation process and shock process,and the dependence of them is that a higher degradation level will lead to a higher probability of traumatic failure,which is caused by shock.After system reliability model is obtained,a condition based maintenance model is developed.The goal of the optimal maintenance scheme is to minimize average long run cost rate by properly choosing the preventive deterioration level and the length of an inspection cycle.A numerical example is provided to illustrate the application of the model,and the sensitivity analysis about system parameters has been discussed.(4)Reliability and maintenance models are presented for system subject to competing failure.System fails due to degradation failure and traumatic failure,degradation failure is caused by the system degradation process,traumatic failure is caused by the external shock process.The degradation process and the external shock process are dependent in two inspects:(1)each external shock lead to system abrupt degradation damages;(2)the degradation affects the traumatic failure threshold,when the total degradation exceeds some value,traumatic failure threshold value changes to a lower level.We assume that the degradation continuously increases following a linear path,and the external shock is considered by three classic shock models,i.e.,extreme shock model,? shock model and m shock model.Based on degradation and three different random shock models,their reliability models are developed for these two dependent failure processes with a shifting failure threshold.Two maintenance strategies are also applied and compared to decide which one is more beneficial.An example is presented to demonstrate the applicability of the proposed models.