Research On Multiple Stresses Accelerated Life Test And Statistical Analysis Of Aerospace Electrical Connector

As the mating elements, hundreds of aerospace electrical connectors play an important role in the aerospace systems for transmitting electric signal, connecting circuit and implementing specific functions. The failure of any set electrical connector will result in the "out of order" system. As a result, the reliability of electrical connector has a direct impact on system whether it can work reliably. However, lack of reliability index of electrical connectors under working stress makes it difficult to carry out the reliability design of system. Electrical connectors would be subjected to a variety of environmental factors in the working status, the related technologies for electrical connectors' reliability assessment under multiple working stresses have hence become important research topics. In this dissertation, the model Y11X-1419 electrical connector is taken as the object, the relevant technologies of accelerated life test for quick assessment of product reliability under multiple stresses have been comprehensively researched.In chapter 1, the background of the research work and important significance of the dissertation were discussed. The developing history and current situation of some crucial techniques at home and abroad, such as the statistical model of accelerated life test, the optimum design of accelerated life test plan and statiatical analysis methods of test data were reviewed, and the existing problems were presented. The current research situation and problems of electrical connectors were generalized. Finally, the main research contents and the frame structure of this dissertation were given.In chapter 2, the reliability statistical model was derived from the failure mechanism. Firstly failure analysis was carried out for aerospace electrical connectors, based on the underlying causes of contact failure, which is insulation film make-up on the electrical connector contacts surface, the law of film growth was researched. To combine with the electrical connectors structural characteristics, by using the asymptotic distribution theory, the derived product contact life follows the two-parameter Weibull distribution. Based on the chemical reaction and fretting corrosion theory, the failure physics equation between connector life and multiple stresses, which is generalized Eyring model, was derived, consequently the reliability statistical model of electrical connectors under multiple stresses of temperature and vibration was set up.In chapter 3, the optimized design method of constant multiple stresses accelerated life test plan under periodic inspection was proposed. According to the reliability statistical model, by using uniformly test theory, the combined mode of different stresses and testing times were determined, with the principle of equal probability for periodic inspection time, the multiple stresses optimized design mathematic model of electrical connector test plan under periodic inspection was proposed. The result about the multiple stresses optimum design of electrical connector accelerated life test plan under periodic inspection shows that the optimized test plan can greatly raise estimation precision of test data. Meanwhile the robustness analysis was carried out for optimized test plan, the result of analysis provides a theoretical basis for the robustness test plan design with the initial selection of model parameters.In chapter 4, the simulation and evaluation's method of multiple stresses accelerated life test plans under periodic inspection was built. Taking asymptotic variance expected value and standard deviation of product median life under normal working stresses level as evaluation criteria of accelerated life test plan's estimation precision and stability respectively, simulation method of multiple stresses accelerated life test under periodic inspection was proposed by the Monte-Carlo method. By using periodic inspection maximum likelihood estimation theory, the mathematic model used for multiple stresses accelerated life test plan's simulation evaluation was built. Meanwhile, taking the asymptotic variance mean and standard deviation of random samples as a substitute for its expected value and standard deviation respectively, simulation evaluation's method of test plan was proposed. The result of simulation evaluation of test plan shows that the proposed optimization theory of multiple stresses accelerated life test plan under periodic inspection is true, and the method of that is feasible. In chapter 5, the versatile maximum likelihood estimation method was used for treating the interval data, the estimation value of electrical connector reliability characteristics was obtained, the reliability level of electrical connectors under working stresses was quantitatively assessed.In chapter 6, the high precision confidence interval estimation method of multiple stresses accelerated life test data was proposed. Based on the two-step fitting regression method, leading the Bootstrap estimate method into regression analysis, by correcting the bias of the Bootstrap estimate value, the Bootstrap regression confidence interval estimate method of reliability characteristic statistics under the condition of small samples was proposed. The simulation result shows that confidence interval is satisfied with demand of confidence degree.In chapter 7, the verification method of reliability statistical model under multiple stresses was proposed. Combining with chart analysis and numerical analysis method, the electrical connector life distribution model was certified by statistical analysis of the accelerated life test data. By transforming the accuracy validation problem of accelerated life model into the coplanarity test problem of spatial data points from the perspective of three-dimensional space, from the point of view of statistical test, accelerated life model under multiple stresses was fitted by multiple linear regression method. Taking the statistic as the test target, which characterizes the relative size of the sum of square of vertical distance between the spatial data points and fitted values, and the sum of deviation square of spatial data, the verification method of multiple stresses accelerated life model by using constant stresses accelerated life test data was proposed, which could quantitatively assess the accuracy of accelerated life model. The verification result of aerospace electrical connectors' reliability statistical model shows that the model can preferably describe the nature of the electrical connectors' life characteristics variation under multiple stresses of temperature and vibration. By further microscopic analysis of Scanning Electron Microscope and Energy Dispersive System, the rationality of the reliability statistical model established from the failure mechanism was proved.Finally main results and conclusions of this dissertation were systematically summarized. The study emphases of the further research work were discussed and forecast.