机械结构的疲劳寿命预测与可靠性方法研究

发布时间：2018-02-08 14:36

本文关键词： 可靠性分析疲劳寿命累积损伤强度退化时变性失效相关　出处：《电子科技大学》2016年博士论文　论文类型：学位论文

【摘要】：随着机械结构服役环境的愈加恶劣以及随机影响因素的日益增加,疲劳作为机械结构主要的失效形式,占失效总数的50%-90%。疲劳现象和机理异常复杂,受到各种不确定因素的影响(材料性能、服役环境、使用时间、荷载效应等)。机械结构的载荷、强度、运行环境等参数都随时间或载荷作用次数等寿命相关指标发生变化,疲劳过程是机械结构随时间的变化,其损伤不断累积的过程,其可靠性也是随时间发生变化的,因此,时变性是机械结构疲劳过程的主要特征,是机械结构疲劳可靠性的一个重要属性,能反映出机械结构性能与系统质量随时间的变化,受到学术界和工业界的关注。传统机械结构疲劳可靠性模型缺乏考虑失效模式的相关性、多部位损伤以及多构件之间的关联,未能全面反映载荷历程、强度退化、结构特征等要素,不能较好地表征并描述工程实际中存在的不确定性因素。因此,难以准确地预测机械结构的疲劳寿命和可靠度。本论文针对目前机械结构疲劳寿命预测模型及可靠性分析方法存在的不足、可靠性试验时间长和费用高等问题,以机械传动装置关键零部件的材料及结构作为研究对象,拟从全寿命周期角度对其在多工况、复杂环境-随机性交互作用下基于失效物理的疲劳损伤累积、裂纹萌生、裂纹扩展机理和疲劳时变可靠性进行研究。对于机械结构设计的改进、制造工艺的提高、安全可靠的运行,具有重要的学术价值和现实意义。本文主要研究内容和研究成果如下：(1)基于累积损伤的疲劳寿命预测。为了提高疲劳累积损伤模型的计算精度,本文基于累积损伤曲线法中考虑载荷的加载顺序以及Carten-Dolna模型中指数“d”的选择,考虑载荷间的相互影响,提出一种改进累积损伤模型,该模型考虑了加载次序以及载荷间相互作用的影响,改进模型的预测寿命精度比现有模型精度有一定的提高。同时,通过对改进模型及现有模型进行评估和对比分析,说明了Miner法则在工程中应用的广泛性。针对传统Miner法则存在的缺点,通过考虑载荷及损伤的分散性以及随机性对疲劳寿命的影响,提出基于模糊理论的Miner法则,该法则考虑载荷之间相互效应和载荷次序对疲劳寿命的影响,保持了传统Miner法则应用简单的优点,通过算例分析,说明了所提模型的可行性与准确性。(2)疲劳裂纹萌生阶段的寿命预测-修正的总应变能损伤函数模型。机械结构的疲劳裂纹形成阶段的寿命,是指从加载开始至结构出现宏观可测裂纹的这一过程。这一阶段受到多种因素的影响,多数情况下这些因素会产生交互作用直至机械结构发生疲劳破坏。本文研究机械传动系统关键零部件材料在多种失效因素共同作用下的力学行为及其对寿命的影响,提出了修正的总应变能损伤模型,该模型综合考虑了外在的加载条件和材料的能量耗散宏观特性等因素对疲劳损伤的影响,有较广的适用范围。研究结果表明,在不同的加载试验条件下,改进模型的预测寿命精度比传统模型精度有一定的提高,可满足工程的需要。(3)疲劳裂纹扩展阶段的寿命预测-修正的裂纹扩展率函数模型。机械结构疲劳裂纹扩展阶段的寿命是指：构件在循环载荷作用下,出现宏观可测裂纹之后,裂纹扩展-破坏的这一过程。由于影响疲劳裂纹扩展的因素众多,扩展机理比较复杂。因此,对疲劳裂纹扩展寿命的预测,目前还没有统一的表达式,如何预测含裂纹构件的剩余疲劳疲劳一直是人们研究的重点。本文通过对以往已提出的疲劳裂纹扩展理论进行分析研究,分析其优点及不足。在此基础上,推导出改进的疲劳裂纹扩展公式,该模型反映了裂纹在三个不同阶段的扩展率,为实现准确的预测机械装备剩余寿命提供有效方法。研究结果表明,相比现有模型,所提模型扩展了现有模型的预测范围,预测精度也有较显著的提高。(4)基于性能退化的失效相关疲劳可靠性分析方法。机械结构在复杂交变载荷作用下,载荷、损伤和环境等不确定因素的分散性和随机性会导致系统特性表现出很大的分散性,要有效进行机械结构疲劳寿命预测与可靠性分析,需切实反映载荷历程的复杂性与不确定性、零部件不同失效模式之间的统计相关性、性能退化与载荷历程之间的关系及退化过程中载荷与应力重新分布、复杂零部件的可靠性对载荷不确定性的依赖性等。本文利用与载荷作用次数相关的动态可靠性模型,考虑疲劳过程中材料强度退化规律、强度的衰减对结构疲劳寿命的影响、材料和载荷的随机性,通过故障物理分析,推导机械结构强度和疲劳寿命的概率分布等,建立了机械结构疲劳时变可靠性分析和评估方法,同时建立了基于失效数据的多失效模式相关的Copula综合可靠性评估模型。
[Abstract]:With the mechanical structure of the working environment and the increasingly harsh random factors increasing as fatigue failure form of mechanical structure mainly, accounting for 50%-90%. of the total fatigue failure phenomenon and mechanism is extremely complicated, influenced by many uncertain factors (material properties, service environment, service time, load effect). Load, mechanical structure the strength of the operating environment and other parameters with time or frequency of loading and other life related index changes, the fatigue process is the mechanical structure with the change of time, the process of damage accumulation, its reliability is also change with time. Therefore, when degeneration is the main feature of the mechanical structure fatigue process, is an important properties of fatigue reliability of mechanical structure, can reflect the performance of the mechanical structure and quality of the system with the change of time, by the academic circles and industry. The traditional mechanical structure The lack of fatigue reliability model considering the correlation of failure modes, the association between multiple site damage and multi component, failed to fully reflect the load history, strength degradation, structural characteristics and other factors, can not be used to characterize and describe the uncertainty factors in practical engineering. Therefore, it is difficult to accurately predict the fatigue life of the mechanical structure and reliability this paper aiming at the shortcomings of fatigue life of mechanical structure prediction methods exist model and reliability analysis, reliability test time and cost, with the materials and structure of the key parts of the mechanical driving device as the research object, from the perspective of the whole life cycle to the operating environment, complex stochastic interaction under the accumulation. Physical fatigue damage failure based on crack initiation, crack propagation and fatigue mechanism of time-dependent reliability is studied. For the design of mechanical structure The improvement, the improvement of manufacturing process, safe and reliable operation, has important academic value and practical significance. In this paper, the main research contents and results are as follows: (1) the fatigue life prediction based on cumulative damage. In order to improve the calculation precision of the cumulative fatigue damage model, the loading sequence and the index "Carten-Dolna D model" the choice of considering cumulative damage curve method based on considering the interaction between loads, proposes an improved cumulative damage model, the model considers the interaction between load and loading sequence, life prediction accuracy of modified model has better accuracy than the existing model. At the same time, through the analysis and comparison of evaluation the improved model of the existing model, explains the universality rule of Miner application in engineering. Aiming at the existing shortcomings of traditional Miner algorithm, by considering the load and damage The dispersion and random effect on fatigue life, fuzzy theory is proposed based on Miner principle, the principle of considering the influence of load between the effect and the loading order on fatigue life, maintains the advantages of the traditional Miner rule application is simple, through the example analysis, the feasibility and accuracy of the model (2) fatigue. Crack initiation life prediction of total strain correction can damage the function model. The stage of formation of fatigue life of mechanical structure, refers to the loading from the beginning to the structure of the process of macro measurable crack. This stage is affected by many factors, in most cases, these factors will interact until machinery the structural fatigue failure. This paper studies material of key parts of mechanical transmission system with multiple failure mechanical behavior of interaction between factors and its influence on the life of the proposed amendment The total strain energy damage model, the model considers the factors of external loading conditions and material properties on the macroscopic energy dissipation effect of fatigue damage, a wide range of application. The results show that the load in different experimental conditions, the life prediction accuracy of improved model is better than the traditional model precision, can meet the needs of the project. (3) prediction of fatigue crack propagation stage life correction crack growth rate function model. The mechanical structure fatigue crack growth stage of life: refers to the component under cyclic loading, macro crack can be measured after the process of crack propagation failure due to many factors. Effect of fatigue crack, propagation mechanism is complex. Therefore, the prediction of the fatigue crack propagation life, there is no unified expression, how to predict the residual fatigue cracked component Has been the focus of research. Analysis of fatigue crack propagation theory has been put forward based on previous analysis, its advantages and disadvantages. On this basis, the improved fatigue crack propagation formula is derived, the model reflects the crack in the three different stages of the expansion rate, provides an effective method for realizing accurate prediction of machinery the remaining life of equipment. The results show that compared with the existing models, the proposed model extends the range of existing prediction model, the prediction accuracy is also significantly improved. (4) the related fatigue reliability failure analysis method based on performance degradation. The mechanical structure in complex load under cyclic loads, and damage and environmental uncertainty dispersion and random will cause the system characteristics showed a great diversity of factors, in order to effectively carry out fatigue life prediction and reliability analysis of mechanical structure, need to reflect the load. The complexity and uncertainty of the statistical correlation between the components of different failure modes, the relationship between performance degradation and the loading history and the degradation of re distribution and stress in the process of loading, the reliability of complex components of load uncertainty dependence. Based on the dynamic reliability model and the frequency of loading, considering the degradation of material in the process of fatigue strength, strength attenuation effect on the structure fatigue life, random material and load, through the failure physics analysis, mechanical strength and fatigue life of the derivation of the probability distribution, reliability analysis and evaluation method to establish the mechanical structure fatigue, and establish the failure data of multiple failure modes based on reliability Copula related evaluation model.

【学位授予单位】：电子科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TH114

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