| As a deterrent and defensive power, the equipments are in a storage stage most of the time. With the increasing demand on reliability, the new equipments have been required to achieve a shelf life up to 32 years, which is a huge challenge to the reliability and the support capabilities of their components, such as electrical connectors, in these systems. Compared with the ordinary electrical connectors, the J599 series small circular ones possess a better resistance to the environment and a higher reliability index, and they are widely used in control, telemetry and security systems, which play a key role for the reliability of the equipments. Even though the current J599 series electrical connectors in our country imitates the US military standard MIL-C-38999, during storage the contact resistances of electrical connectors may increase, resulting in product failure as well as other problems. The J599 series electrical connectors cannot meet the 32 years’ shelf life requirement, thus, how to achieve the quantitative design and verify their reliability in a short time remains a very urgent issue.The J599III/26(20)FA35 electrical connector was selected as a typical representative in J599 series electrical connectors under the ’long-term storage and one-shot application’ background of this dissertation. After analyzing the stresses and failure modes in the storage environment and understanding the failure mechanisms, a reliability statistical model was established based on the structures size and material parameters of electrical connectors. The reliability design model of the electrical connectors, the long-life design method, and the optimal design method of accelerated degradation test were studied. A rapid evaluation method to estimate the storage reliability of electrical connectors was also provided, which can help the J599 series electrical connectors to reach their proposed long shelf life requirements.There are eight chapters in this dissertation and the main content of each chapter is as follows:Chapter 1 described the background and discussed the significance of this research. The current research status and the remaining problems in the reliability design, the accelerated degradation test technology, and the reliability of electrical connectors were introduced. The main research content and the frame structure of each chapter were proposed too.Chapter 2 analyzed the structure, the material, and the function of each part of the J599III/26(20)FA35 electrical connector. The various types of stresses in the storage environment and their effects to electrical connector’s key performance parameters, such as the contact resistance and the insulation resistance, were discussed. All of the failure modes of the electrical connector in the storage environment were given out and contact failure was determine as the main failure mode. The failure mechanism of electrical connector was studied from the microscopic perspective.In chapter 3, based on the failure mechanisms, the microstructure of the electrical connector’s contact surface was analyzed. By using the reaction kinetics, the relationship between the contact resistance and the structure, the material, the surface morphology, and the contact pressure of the electrical connector was derived. Combined with the life model of the electrical connector, a long-life design model of electrical connector under the storage conditions was established, and the methods to determine the model’s parameters were discussed.In Chapter 4, an optimized design method in the constant stress accelerated degradation test was put forward according to the degradation model of the electrical connector. A non-optimized traditional accelerated degradation test plan and two- stress unequal distribution test plan were discussed by comparing their estimated accuracy and robustness. Considering the advantages and disadvantages of these accelerated degradation test plans, a compromised test plan was proposed. Finally, the compromised accelerated degradation test plan was determined under actual conditions and its robustness was analyzed too.In Chapter 5, by using the asymptotic variance of the estimated logarithmic life median under normal stress levels as the target, the estimated accuracy and the robustness of the accelerated degradation test plan determined in chapter 4 were evaluated by maximum likelihood method based on Monte Carlo simulated data. The results verified the correctness of the optimized design theory for accelerated degradation test and the rationality of the adjusted compromised accelerated degradation test plan.In Chapter 6, with products’ constant stress accelerated degradation test data, the accelerated degradation model parameters were estimated by using maximum likelihood estimation method, and the shelf life and the reliability of the electrical connector in the storage environment were also estimated. The bias-corrected Bootstrap method was introduced into the test data confidence interval estimation, and the confidence interval of electrical connector’s logarithmic life median was reached in different confidence levels. Finally, the Bootstrap method was evaluated by simulation. The results showed that the electrical connector produced by using the long-life design can satisfy the demands and hence the long-life design model is correct.In Chapter 7, a verification method of accelerated degradation model was proposed on the basis of the accelerated degradation test data. The degradation path model and the accelerated degradation equation were examined by probabilistic graphical and numerical analysis; the results verified the correctness of the model. The correctness of the failure modes and mechanisms was further verified by the microscopic analysis with Scanning Electron Microscope and Energy Dispersive Spectroscopy, and the rationality of the reliability statistical model and the design model was proved.At last, chapter 8 summarized the whole work of this dissertation, emphasized its innovations, and gave some suggestions for the future work. |
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