Research On Reliability Evaluation And Life Test Methods For Space Relays

Space relays are the indispensable key components used in defense weapon systems and aerospace products for completing power distribution, signal transmission, circuit isolation and load switching. Life test for space relays is a compulsory sampling test before the products go out. Generally, contact voltage drop and open-circuit voltage are observed during the current life test. Because the information obtained from the two parameters is too limited, it is difficult to further reveal the degradation process and failure mechanisms of the products, and it is hard to describe the influences of different test conditions and product structures on the reliability of the relays. These disadvantages result in the inapplicability of the current life test for guiding product design and accelerating product reliability growth.To comprehensively analyze and evaluate the reliability of space relays, a new reliability life test method for space relays based on performance degradation is proposed in this paper. Based on the analysis of failure mechanisms, the modeling degradation trace, life prediction and reliability assessment methods of space relays are extensively investigated by analyzing the variations of several parameters recorded during life test.Currently, post-analysis method is applied to analyze the failure mechanisms of space relays, which is lack of generality and easy to overlook soft failures. A method for discriminating contact failure modes and failure mechanisms based on degradation parameters is proposed in this paper. Many kinds of contact soft failures, such as abnormal time parameters, sustained arcing and excessive rebound duration, are detected by analyzing the variations of several degradation parameters including overtravel time, rebound duration, closing time, etc. The principal component analysis method and distance discriminant analysis method are adopted to extract variations of contact gap from these degradation parameters. After that, the classification and discrimination of contact failure mechanisms of hard failures are accomplished. The surface morphologies and chemical compositions of the failure contacts are also analyzed, and the results indicate the discriminant methods used in this paper are valid.Degradation trace modeling method based on the thorough analysis of failure physical and chemical law has become a main reliability prediction method of products. The Fisher discriminant criterion is employed to determine prediction variables that are very sensitive to contact performance degradation of space relays. Furthermore, a preprocessing method based on wavelet transform and stationary time series analysis is introduced to reduce the impact of interference of the prediction variables on the accuracy of the model. To fully consider the influence of arcing energy, product structure, contact material and sample dispersion on degradation of contact gap, the physical-of-failure degradation model of space relays is established according to cumulative damage theory. The parameters of the model are estimated by regression analysis method and the average prediction accuracy of this model is up to 70%.The current reliability assessment method of space relays assumes the product distribution is subject to exponential distribution which means a constant failure rate at any time. However, the assumption is not very reasonable. Consequently, a fuzzy comprehensive evaluation method is introduced to determine the most appropriate distribution type. With the consideration of the contact failure mechanisms, the reliability assessment methods for degradation failure of space relays are proposed based on failure statistical model and stochastic process. Then the assessment of various samples in different failure mechanism is realized according to the multi-parameters statistical model, and the error between the assessment results and the practical reliability value is less than 5%.Finally, a reliability evaluation and life test system for space relays is designed and accomplished in this paper. A synchronous, high-speed, multi-channel, multi-sample dynamic waveform acquisition unit is developed based on CAN-bus.According to the waveform data of the tested relays, the software algorithms for calculating each degradation parameter are designed and implemented. The PC software is developed to carry out these methods including failure mechanism discrimination, degradation trace modeling, life prediction and reliability assessment of space relays.The degradation parameters are fully utilized for analyzing the reliability of space relays, and the proposed methods also can be applied to other switching devices with similar structures.