Research On Theory And Method Of Reliability Demonstration Based On Accelerated Test

During the reliability demonstration of the equipment, the test plan is designed according to the reliability target, and whether the reliability level of the equipment achieves the requirements is judged using the test data. Reliability demonstration is the necessary and key point for confirming the reliability level of the equipment, which plays an important role in maintaining the usable rate and exerting the benefit of equipment. However, the test time of the traditional reliability demonstration test method is long and their efficiency is low. It is difficult to support the reliability demonstration of the equipment with high reliability and long life.Aimed at the requirement of reliability demonstration for the equipment, the theories and methods of reliability demonstration based on accelerated test are developed for the components(including the products with catastrophic failure modes, the products with degradation failure modes, and the products with competing failure modes) and systems. The main contributions are summarized as follows:1. Methods of reliability demonstration based on accelerated test for the products with catastrophic failure mode are developed.(1) With the known design parameters, the reliability sampling function under the acceleration condition for log location-scale distribution is developed. The method of designing the accelerated life test sampling plan(ALTSP) is presented. It is available for the cases involving various types of reliability targets, such as reliability at the specified mission time, lifetime at the specified reliability and so on.(2) The method of reliability demonstration based on step-stress accelerated life test(SSALT) with the unknown design parameters is presented. The method of optimal design for SSALT based on equivalent decision rules is proposed using the prior values of design parameters; with the SSALT data, the ALTSP and the decision method are also developed through minimizing the local asymptotic variance of the risk function.2. Methods of reliability demonstration based on accelerated test for the products with degradation failure mode are developed.(1) With the known design parameters, the definition and measurement methods of the risk caused by degradation measurement fitting based on degradation path model are presented, and the method of designing the hybrid accelerated test sampling plan(HATSP) is developed. The results show that the test time can be shortened and the cost can be reduced remarkably using the HATSP than using the ALTSP.(2) The method of reliability demonstration based on step-stress accelerated degradation test(SSADT) with the unknown design parameters is presented. The method of simulation-based optimal design for SSADT based on equivalent decision rules is developed using the prior values of design parameters; with the SSADT data, the HATSP and decision method are also developed.3. Methods of reliability demonstration based on accelerated test for the products with competing failure modes are developed.The reliability sampling function under acceleration condition cannot be developed due to the complexity of the model under competing causes of failure. Therefore, the method of reliability allocation involving the risks is developed, where the requirement of reliability level and risk for reliability target are allocated to each failure mode. According to the allocated reliability targets, based on ALTSP and HATSP for the products with a single failure mode, the methods of designing the accelerated test sampling plan for different types of failure modes are developed, which include the multiple catastrophic failure modes, multiple degradation failure modes, and both catastrophic and degradation failure modes. The accelerated test techniques can be applied for reliability demonstration of the products with competing failure modes using the proposed method.4. Methods of system reliability demonstration based on accelerated test of the components are developed.The method of system reliability target transformation is developed, where the system reliability target with long mission time or long lifetime is transformed to the target with short mission time utilizing the data from accelerated test of components. The system reliability synthesis method based on the accelerated test of components is presented, where the the equivalent binomial system data at the mission time of the transformed target is calculated. According to the transformed target, the system reliability acceptance sampling plan and the decision method are developed to accomplish the demonstration using the equivalent binomial system data.5. The proposed methods in this dissertation are applied to demonstrate the reliability target of the air pressure controller of an engine.In summary, drawn by the application requirements of the reliability demonstration of the equipment, the reliability theories and methods based on accelerated test for different types of the products are researched systematically in this dissertation, including the methods for the components with catastrophic failure modes, the components with degradation failure modes, the components with competing failure modes, and systems. The research results are meaningful for the application and research of accelerated test techniques in the reliability demonstration of equipment.