Research And Applications On Mechanism Of Intermittent Failures In Extreme Vibration Environment And Online Diagnosis Technology

The intermittent fault has the characteristics such as strong randomicity and short lasting time, which make it is hard to be detected and may bring huge harm to the equipment. Statistical data and failure analysis has shown that vibration environment is one of the main causes of equipment intermittent faults. Especially in the extreme vibration environments, the vibration randomicity is stronger and the stress severity is higher, which makes the intermittent fault problem more prominent. Therefore, how to diagnose intermittent faults caused by the extreme vibration environments online is a tough problem that needs to be solved.Aiming at the intermittent fault problems under extreme vibration environment, this paper systematically analyzes the mechanism and rules of intermittent fault modes induced by extreme vibration environment. It also establishes the relationships among extreme vibration environment, equipment components cumulative damage and intermittent faults. Besides, it studies intermittent fault diagnosis method based on cumulative damage and HMM(Hidden Markov Model, HMM) under extreme vibration environment.The main contents of the dissertation are as follows:1. Mechanism and regularity analysis of intermittent faults induced by extreme vibration environment.This paper gives a definition of extreme vibration environments and the environment stree scopes that the equiment can withstand. It systematically analyzes the mechanism and laws that how the extreme vibration environmental stress induces intermittent fault. A connecting component of the equipment is taken as an example. The finite element simulation model of the component is established and the influences of key characteristics parameters of extreme environmental stress vibration(root mean square value of vibration acceleration extremes, extreme vibration frequency) on the intermittent faults are analyzed.2. Relationship analysis of extreme vibration inducing intermittent faultsExtreme vibration environment stress can accelerate the component cumulative damage and eventually leads to the intermittent faults. For this problem, the paper proposes the component cumulative damage calculation method under extreme vibration environment based on elastic-plastic stress theory. With this method, a HMM-based Tri-State(normal state, intermittent state, fault state) injury relationship model is built, which describes the relationship among environmental stress of extreme vibration, component damage and component relationship between intermittent faults.3. HMM intermittent fault online diagnosis based on cumulative damage under extreme vibration environment.For the uncertain characteristics of intermittent faults caused by extreme vibration environment, with the Tri-State HMM-based damage relationship model, the cumulative damage based HMM intermittent fault diagnosis model is constructed, in which the model parameters are optimized. A fault diagnosis method is proposed based on the diagnosis model to take a real-time diagnosis on the intermittent fault.4. Verification and application of intermittent fault diagnosis technologyFor a helicopter attitude indicator, a software which can calculate the cumulative damage of key components and diagnose intermittent faults is developed. Relevant tests are carried out under extreme vibration environment and the test data is analyzed to verify the validity of the proposed method. The results show that the proposed method is of remarkable effectiveness in real-time diagnosis on intermittent fault.