Research On Preventive Replacement Policy With Uncertain Lifetime Distribution Of Civil Aircraft Structure

As the civil aircraft works in a special environment with high altitude,temperature,pressure and speed,it can easily result in the degradation and failures of some aircraft structure components.Due to the absence of the historical operation data for a new type of the components,we can only gain the belief degree of the components' lifetimes through experts' knowledge and experience.However,the probability theory may not explain the subjective uncertainty of experts' belief.As an effective tool in dealing with subjective reliability,uncertainty theory provides an important theoretical approach to solve such problems.Firstly,the definition of the failure distribution function of the component with uncertain lifetimes and the mathematical expression of the failure rate based on belief degree of experts are given.We also discuss the failure rate function of components,whose lifetimes have common uncertainty distributions.Assume the lifetimes of structure components have uncertainty distributions,an optimal preventive replacement policy with the stock tolerance limit is studied.Meanwhile,considering the different maintenance requirements,the preventive replacement models with three optimized rules are proposed to search the optimal replacement period: a)the expected value model to minimize the average cost with a block replacement period;b)the chance value model minimizing the measure of the average replacement cost beyond the budget;c)the key value model to constrain that the measure of the average replacement cost below the budget exceeds a given confidence.Finally,numerical examples are given to verify the validity of the proposed model.And then,an extended renewal reward theorem is proposed,and the limit distribution theorem is given.The operation times and the maintenance times of the structure components are assumed to be uncertain variables and random variables,respectively.The proposed extend renewal reward theorem is applied to the preventive replacement policy with limit maintenance time.Taking the planned maintenance time T as the decision variable,and an uncertain random programming model with the minimum average maintenance cost rate as the objective function is established.The expected cost rate function is analyzed,and the existence condition of the optimal planned maintenance time T* is found.The validity of the model is verified by an example,and the sensitivity analysis of the distribution function parameters and cost parameters are carried out.The research results of this paper provide theoretical support for developing maintenance and replacement policy of new aircraft structure component,which can ensure optimizing aircraft structure component reserve and reducing maintenance and replacement costs.