| With the increasingly harsh environment service and random factors influence, fatigue is the main failure mode of the mechanical structure, which accounts for the total failure of 50%-90%. The phenomenon and mechanism of fatigue are very complex, which are influenced by various kinds of uncertain factors (such as material properties, service environment, time of use, load effect, etc.). Mechanical parts of the load, strength, operating environment parameters changes with time or times of load and life index, the fatigue process is dependent on the time of the damage cumulative to the time, its reliability is changing. Therefore, time-dependent is the main features of the mechanical structure fatigue, is one of the most important attributes of component fatigue reliability, can reflect the performance of components and system quality changes with time, subject to the attention of academia and industry. Traditional reliability model fails to completely reflect the effect of complicated random load history, strength degradation and structure geometry. Which can’t describe the uncertainty factors in engineering practice. Therefore, it is difficult to accurately predict the fatigue life and fatigue reliability of structures.This dissertation aims at the problem that the fatigue life prediction and reliability analysis method is insufficient, the reliability test time is long and the cost is high, with mechanical transmission device key parts as the research object, intends to the perspective of the whole life cycle of the conditions, environment is complex and random interaction based on failure physical fatigue cumulative damage and crack initiation, crack propagation mechanism, time-dependent fatigue reliability. For the improvement of the design, manufacturing process, to achieve a safe and reliable operation of major mechanical structure, has important practical and strategic significance.The main contents and achievements of this dissertation are summarized as follows:(1) Fatigue life prediction based on cumulative damage. In order to improve the accuracy of fatigue damage accumulation, and expand its application range, it is necessary to modify the traditional fatigue damage accumulation model. This paper based on the cumulative damage curve method considering load sequence and Corten-Dolan method index’d’considering the load interaction, a modified damage model is proposed. This model considers not only the load sequence effects, but also the effects of load interaction, thus it has a wider applicability. In addition, through modified damage model and the existing model evaluation, comparative analysis, the extensive application of Miner rule in engineering is explained. And then for the shortcomings of traditional Miner’s rule, by considering dispersion and randomness of load and damage on the fatigue life, a Fuzzy Miner’s rule is developed, which consider the mutual effect between the load and the load order of the fatigue life prediction, maintaining the traditional advantages of simple applications Miner rule, by a numerical example, to verify the accuracy and feasibility of the proposed model.(2) Fatigue life prediction of crack initiation stage-development of a generalized energy-based damage parameter for fatigue life prediction. Fatigue crack formation stage of mechanical structure, which is from the beginning to the macro-structure of the process can be measured cracks appear. This stage is affected by many factors, in most cases, the interaction of these factors until the fatigue failure. In this paper, we study materials of the key parts for transmission system in a variety of failure factors on the mechanical behavior and its impact on life expectancy and generalized total strain energy damage model is proposed and the model considering the external loading conditions and material energy dissipation macro characteristics due to the prime influence on fatigue damage, has a wide scope of application. The results show that, under different loading conditions, the life forecasting precision of the improved model is more precise than the traditional model is improved and can meet engineering needs.(3) Fatigue life prediction of crack growth stage-development of a generalized crack growth rate function model for fatigue life prediction. Fatigue crack propagation life of mechanical structure is the process of fatigue crack growth and failure under alternating load. Due to the fatigue crack propagation mechanism is complex and affected by many factors. Due to fatigue crack propagation mechanism is very complex, and affected by many factors, Therefore, there is no unity of fatigue life estimation of crack propagation of quantitative analytical expressions, and how to determine the crack growth rate has been a hot research topic. In this paper, the fatigue crack propagation theories have been proposed to analyze, and its advantages and disadvantages are analyzed. On this basis, to derive the generalized fatigue crack propagation equation, the model reflects the crack growth rate in three different stages, providing an effective method for accurate prediction of complex structures remaining life of machinery and equipment. The results show that, compared to the existing model, which extends the scope of existing models predict, and the prediction accuracy is significantly improved.(4) Fatigue reliability analysis of the performance degradation by considering the correlation of multiple failure modes. The system under the action of complex alternating load, the dispersion and randomness of the uncertain factors such as load, damage, environment and so on, which lead to the great dispersion of the system characteristics. To truly realize the fatigue life and reliability design goal, need to effectively reflect the load history of complexity and uncertainty, different parts failure mode between the statistical correlation, performance degradation, and the relationship between the load history and degradation process load and stress re-distribution, complex parts of the reliability of the uncertainties of load dependent. In this paper, the dynamic reliability model is used which associated with the load number. The key technology lies in considering the fatigue strength of materials performance degradation and strength attenuation to influence the life of the structure, material and load randomness, through physical failure analysis and derivation of structural strength and fatigue life probability distribution, to establish system fatigue time-dependent reliability analysis and evaluation method. In addition, the comprehensive evaluation model of reliability is established based on failure data considering the correlation of multiple failure modes with copula function... |
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