| The electrical connector is an important basic component for transmitting electric power and electric signals,and is also one of the weak links in military equipment system.Therefore,accurate evaluation of electrical connector reliability is of great significance to the life and longevity of missile equipment.The current assessment methods for the storage life of electrical connectors have only considered the inventory environment,but neglected the effects of tasks such as maintenance,testing,transportation,training,and combat duty,resulting in inaccurate evaluation.In order to make the test environment more in line with actual storage environment,effects of discrete stresses in the task profile are considered.A degradation model of contact performance of electrical connectors based on failure mechanism is established,and an optimization method of accelerated degradation test design based on the combination of continuous stress and discrete stress is established.Finally,the accelerated degradation test are carried out with the Y11 P type electrical connectors,and the storage life of electrical connectors are successfully evaluated when considering the mission profile.In the first chapter,the history of reliability engineering and the development of accelerated life test are introduced.The current research status of performance degradation modeling methods,accelerated degradation test design methods and reliability of electrical connectors are summarized.The insufficientes of current research on accelerated degradation test methods and the shortcomings of quantitative reliability evaluation for electrical connectors are pointed out.The objective and main content of the research are established.In the second chapter,in order to explore the micro-mechanisms that leading to performance degradation of electrical connectors during storage time,the stress profiles under storage environment are depicted,and the failure modes,causes,mechanisms of electrical connectors are analyzed.The results show that the temperature and the insertion force have a significant influence on performance degradation of electrical connectors under storage environmental conditions.The contact failure is main failure mode of the electrical connectors,and its mechanism are characterized by the oxidation and corrosion of substrate material.Under temperature stress condition,the growth law of oxidation and corrosion is cubic,while under temperature-plug stress condition,it is a stepwise incremental curve.In the third chapter,based on the positional relationship between corrosions and contact spots on surface of connectors,a geometric probability model for oxidation and corrosion is established.The contact performance degradation model is derived by using the probability limit theory as a nonlinear Wiener process,and the model appears as a nonlinear Wiener process with a variable point when considering the insertion force.A computer simulation model is established by using geometric circle equivalent to replace the oxidized corrosions and contact spots,which is used to simulate the change law of contact resistance.And the simulation results are very similar to the experimental results.In Chapter 4,taking Arrhenius model as the failure physics equation,the normalization method of the accelerated stress is given,and acceleration factor is used to calculate the discrete stress time interval,thus achieving an equivalent time interval conversion at different stress levels.An accelerated degradation test design method based on continuous stress and equally spaced discrete stress is proposed.A group sequential test scheme is designed,and the optimization method has two objectives: aiming at the minimum asymptotic variance of P-fractional life and aiming at the maximum amount of Fisher information.The optimal test plan is obtained under the condition of cost constraints,and the compromise test plan is designed by staggering the test stress levels,comparing with the traditional test plan,the results show that the optimal test plan has good estimation accuracy and poor robustness,and the compromise test plan is the opposite.In Chapter 5,by using the maximum likelihood estimation and the least squares estimation,a two-step estimation method for estimating the parameters of the degradation model and the parameters of the failed physical equation is established.And in order to improve the robustness of the estimation,a least squares estimation method with added data is established to estimate the parameters of the failure physical equation under temperature-plug stress conditions;Accelerated degradation tests were carried out,and the life assessment works under normal temperature stress and temperature-plug stress conditions are completed.By comparing the two sets of evaluation results,it is shown that the plugging stress causes the storage life of the electrical connector to be significantly reduced,and the longer the storage time,the more significant the influence of the plugging stress on the storage life.In order to verify the correctness of the model and the evaluation results,a verification test considering temperature and plugging stress is designed.The box-line diagram method,residual analysis method and variance analysis method are used to analyze the experimental data.And the results show that the characteristics of data drift and diffusion are very consistent with the model,in addition,the increment of data satisfy the independent incremental nature of Wiener process,which verify the validity of the model.Electron microscopy is used to analyze the surface topography and elements of the connectors,and the results show that the contact surface damage is caused by plugging stress,and the oxide film with uniform thickness is not formed on the surface of connectors,but it is attached to the surface by oxidation and corrosion deposits,which verifies the rationality of failure mechanism analysis.In Chapter 7,the conclusions,innovations,deficiencies of this paper and further research prospects are summarized. |
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