Reliability Modeling And Assessment For Numerical Control Equipment With Multi-degradation

Nowadays,the modern numerical control(NC)equipment has some new features,such as limited data,long lifetime,and no failure data,and so on.These new features make the traditional reliability assessment method which is based on a lot of failure lifetime data not efficient to solve the reliability issues.Facing these challenges,the reliability assessments methods based on the performance degradation data has been found timely and become a hot spot of reliability analysis methods for NC equipment gradually.At present,many papers about reliability modeling methodologies for systems have only one performance characteristic and their application range have restriction.In this thesis,the products with multi-performance degradation have been discussed.This thesis makes use of many approaches,such as the stochastic process,Copula theory,impact theory and Markov Chain Monte Carlo(MCMC)algorithm,to establish the reliability model.There are two aspects included in this paper,which are multiple performance degradation modeling and dependent competing failure modeling.The major contributions of this thesis are shown as follows:(1)A reliability model for the products with dependent competing failure process is given to solve the system reliability problem facing both sudden and degradation failure.Firstly,we describe the degradation process via degradation values distribution and use Poisson process to describe the shock process.In addition,the model uses the additional degradation increment to describe the impact of shock process on the degradation process of products.Finally,an illustrative example is given to demonstrate the effectiveness of the proposed model.It proves that the shock process can speed up the degradation process of the product and make the reliability of the products decline more rapidly.(2)Reliability model of products with multivariate correlated degradation process is proposed.In this paper,the marginal degradation process is described via Wiener Process.For the multiple degradation model,the key problem is how to describe the correlation between multiple performance degradation characteristics.To resolve this key problem,we introduce the theory of Copula functions.After establishing the reliability model,a two-stage parameter estimation method based on Bayesian theory has been proposed to compute the unknown parameters.Finally,an illustrative example is given and the results show that the proposed model is more accurate than the traditional model which is based on the assumption that multiple degradation process is independent.(3)A multivariate correlated competing failure model considering effective shock threshold is given.The traditional model tends to think that every shock process always has an impact on the degradation process.However,this assumption does not conform the engineering practice completely.In this paper,we make a more detailed classification of the shock process by introducing the concept of effective shock threshold and develop an improved model based on it.What's more,a reliability modeling method of the products considering the correlation between sudden failure mode and multiple degradation failure mode is proposed.Finally,an illustrative example is given to verify the validity and rationality of the proposed model.