【作者】 朱顺鹏；

【导师】 黄洪钟；

【作者基本信息】 电子科技大学 ， 机械电子工程， 2012， 博士

【摘要】 随着现代机械装备向大型化、复杂化和精密化方向发展,诸如航空发动机、重型燃气轮机等重大机械装备的大量零部件在十分恶劣的环境下工作,需满足高性能要求并实现安全可靠地运行。其中,重大机械装备高温复杂结构(如燃汽轮机和航空发动机热端部件)的寿命和可靠性是制约整机寿命和可靠性水平的主要因素之一。在重大机械装备服役过程中,由于不断的起动、停车以及各种任务的需要,其各部件承受复杂载荷作用,同时诸多不确定性因素愈加恶劣的影响使得复杂构件产生多种形式的失效破坏且表现出较大的分散性。特别是疲劳破坏,对装备的安全工作造成极大的威胁。因此,研究并保证此类结构在这些不确定因素影响下因疲劳断裂而失效的可能性降至最低程度具有重要的现实意义。复杂载荷、多环境因素以及多种失效模式下的寿命预测一直是寿命预测领域的难点和热点。由于重大机械装备复杂结构破坏机理的复杂性、不确定性和分散性,本文针对其寿命预测与可靠性理论中若干亟待解决的重要问题,在复杂载荷、多环境因素以及多种失效模式下的概率寿命预测以及不确定性分析方面展开研究,利用航空发动机涡轮盘用GH4133合金和某型航空发动机实测转速循环数据,并辅以高强度耐热钢试验数据进行模型验证。其主要内容和研究成果如下:(1)提出了复杂载荷作用下考虑小载荷损伤与强化的模糊Miner法则为了完善工程中应用较广的Miner法则的理论缺陷和拓展其应用范围,通过考虑载荷和损伤的分散性和随机性对疲劳寿命和疲劳特性分散性的影响,将复杂载荷中小载荷的损伤与强化引入到传统Miner法则的理论框架下,并将载荷之间相互作用和载荷次序效应对疲劳特性的影响定量地纳入Miner法则,提出了模糊Miner法则。该法则的提出为工程中“载荷是否产生损伤”的判据和“低载强化”现象的解释提供了理论支撑,更符合客观实际。(2)建立了多种失效模式下的寿命预测模型——广义应变能损伤函数模型为统一表征高温复杂结构在多种失效模式下不同载荷类型造成的损伤而实现不同加载波形下的疲劳-蠕变寿命预测,基于能量准则,提出了广义应变能损伤函数模型。该模型综合考虑了各加载条件对其损伤和寿命的影响,具有较广的适用性。在此基础上,考虑到该模型中给定的应变能与控制裂纹形成与扩展的真实应变能的差异,提出了改进型广义应变能损伤函数模型。研究结果显示,在不同温度、应变比或应力比下,改进模型的寿命预测精度较高,可满足工程实际需要。(3)提出了多种失效模式下的寿命预测方法——广义能量损伤参数法针对高温下无荷载保持时间的低周疲劳失效,结合故障物理失效分析技术,从能量角度提出了更具一般性的广义能量损伤参数。在此基础上,应用动粘性来描述损伤累积,提出了一种物理意义更明确和试验依据更充分的延性耗竭模型。广义能量损伤参数和延性耗竭模型均是基于疲劳失效过程中不可逆延性耗散且材料逐渐递减的固有能量吸收能力而提出的,为实现可靠预估重大机械装备复杂构件的剩余寿命提供了有效途径。研究结果显示,相比现有模型和方法,广义能量损伤参数和延性耗竭模型在寿命预测精度和应用范围上有着显著的优势。(4)构建了混合概率故障物理寿命预测理论框架为了解决复杂结构寿命预测中诸多因素引入的不确定性问题,应用Bayes推理和故障物理技术,将寿命预测模型参数、载荷历程和材料属性等参数以分布形式输入,构建了由历史记录数据到材料试验、加速寿命数据的混合概率故障物理寿命预测理论框架。同时,设计并应用马尔科夫链蒙特卡洛(MCMC)仿真技术解决了该框架下高维Bayes推理的密集计算问题。该框架的提出,实现了故障物理技术在疲劳寿命预测中的应用,并可依据不同阶段的信息和知识状态进行信息更新,一方面节省了相关试验时间和成本,另一方面为实现重大机械装备的安全评估和寿命周期管理做出最有利的决策和判断提供了理论依据。(5)提出了基于综合不确定性分析和Bayes推理及信息更新的概率故障物理寿命预测方法基于混合概率故障物理寿命预测理论框架,系统地研究了物理不确定性、统计不确定性和模型不确定性对寿命和损伤的影响,提出了寿命预测中的综合不确定性分析方法:White-Box法,有效地对重大机械装备复杂构件进行概率故障物理寿命预测。同时,拓展了Black-Box法在疲劳寿命预测中的应用,较好地表征并评估了模型不确定性。相比Black-Box法,White-Box法综合考虑了模型、模型参数、材料属性和模型输入变量的不确定性对疲劳寿命的影响。上述两种方法的提出和拓展,为模型的选择和比较提供了一种更为科学的理论依据。研究结果表明,概率故障物理寿命预测方法较好地解释了同一类设备或复杂构件在相同使用条件下寿命也有很大的分散性问题,可用于重大机械装备复杂构件的安全评定、健康监测、结构设计和剩余寿命估算等一系列工程实际问题中。更多还原

【Abstract】 With the rapid development of larger, more complex and precise modern mechanical equipments, some special requirements for designing these complex structures, i.e. mechanisms and reliability, have been brought forward correspondingly. Examples of such structures are the turbine disks used in gas turbine aero-engines and/or heavy duty gas turbines. During operation these disks are subjected to high temperature, pressure and rotating speed conditions, for which a failure could lead to catastrophic results. The life and reliability of these complex structures have been one of the primary factors that restricted the development of major mechanical equipments.For turbine disks during service, the demands of the start-up, normal operation and shut-down phases result in different failure modes, like fatigue and creep which are affected by many uncertainties typically exhibit random behavior. Low cycle fatigue (LCF) at high temperature is a key failure mode of these structures. In order to reduce weight and improve the working life while keeping or increasing reliability, an accurate algorithm for probabilistic LCF life prediction of complex structures is essential, which is the main purpose of this contribution.LCF at high temperature is an interactive mechanism of different processes such as time-independent plastic strain, time-dependent creep and environmental corrosion, and the complex interaction between them. These damage mechanisms under multi-environmental factors make it difficult to predict LCF life using a unified model that can make accurate life prediction for fatigue-creep interaction. According to the complexity, uncertainty and scatter in the fatigue failure mechanism, the overall objective of this dissertation is to address key challenges and critical issues in life prediction and reliability analysis on major mechanical equipments. In this dissertation, probabilistic LCF life prediction models and uncertainty assessment methodologies were studied systematically in both theoretical and engineering applications. The studied alloys included Ni-base Superalloy GH4133, GH4698 (typically used as the turbine disk material in gas turbine engines) and pearlitic heat resisting steel (which is used in steam turbine items). The main work and innovative contributions of this dissertation are as follows:(1) Development of a Fuzzy Miner’s rule considering damaging and strengthening of low-amplitude loads under different load sequencesDue to the shortcomings of the traditional Miner’s rule, a Fuzzy Miner’s rule is developed to consider the strengthening and damaging of low-amplitude loads with different load sequences. This model improves the application of the traditional Miner’s rule, by considering not only the damaging and strengthening of low-amplitude loads, but also the load sequence effects. To apply the Fuzzy Miner’s rule, the law of selecting membership functions for different load spectrum is found and different membership functions are investigated to show the important influence on estimating fatigue life. Applicability of the method was validated using experimental and real-time data gained from aircrafts. It was also found that the predicted fatigue life by the proposed rule is more accurate and reliable than that by the traditional methods. In addition, the Fuzzy Miner’s rule provides a criterion for judging if“the loads cause damage or not”and a theoretical basis for explaining the“coaxing effect”phenomenon in engineering.(2) Development of a generalized strain energy damage function model for fatigue-creep life predictionThe fatigue-creep interaction is a key factor for the failures of many complex structures under high temperature and cyclic loading. These fatigue-creep life prediction issues are significant in selection, design and safety assessments of those components. In order to describe the accumulation and development of damage uniformly and accurately, a generalized strain energy damage function model was developed for fatigue-creep life prediction under different loading waveforms. The approach used in this model to reflect the effects of time-dependent damaging mechanisms on fatigue-creep life is different from those used in all earlier models. In addition, an improved generalized strain energy damage function was used to reduce the difference between the approximate strain energy and real strain energy absorbed during the damage process. This proposed model can describe the effects of different time-dependent damaging mechanisms on fatigue-creep life more accurately than others, which makes it widely applicable and a precise method to predict the life of fatigue-creep interaction.(3) Development of a generalized energy-based damage parameter for fatigue-creep life predictionBased on the plastic strain energy density (PSED) and Physics of Failure (PoF) analysis, a generalized energy-based fatigue-creep damage parameter was developed to account for the creep and mean strain/stress effects in the LCF regime. Moreover, the mechanism of cyclic hardening is taken into account within this model. On this basis, it is assumed that damage accrues by means of viscous flow and ductility consumption is only related to plastic strain and creep strain under high temperature LCF conditions. Based on the ductility exhaustion (DE) theory, a new viscosity-based life prediction model was introduced by using dynamic viscosity to describe the flow behavior. Both the proposed damage parameter and viscosity-based model provided a better prediction of GH4133’s fatigue behavior when compared with the SWT and PSED methods. Under mean strain conditions, these two models provide a more accurate life prediction of GH4133 than that under zero-mean strain conditions, which provides an effective, reliable and new way for accessing the remaining life of complex structures.(4) Construction of a hybrid probabilistic PoF-based LCF life prediction frameworkProbabilistic life prediction of complex structures, such as aircraft turbine disks, requires the modeling of multiple complex random phenomenas. The Bayesian approach can potentially give more complete estimates by combining test data with technical knowledge available from theoretical analysis and/or previous experimental results, and provides many practical features such as a fair coverage of uncertainty and the updating concept that reduces costs and saves time. A hybrid probabilistic PoF-based framework for life prediction using Bayes’theorem was developed to quantify the uncertainty of material properties, total inputs and model uncertainty resulting from creation of different deterministic models in a LCF regime. In practice, the statistical inferences in this framework involve high-dimensional integrations that usually are very computationally intensive. The Bayesian inference was solved using the MATLAB platform to run the necessary MCMC simulation, which greatly improves the utility of this framework. Through this framework, a basis for safety assessment and life cycle management of major mechanical equipments was offered.(5) Development of a hybrid probabilistic PoF-based fatigue life prediction methodology under Bayesian information updating and uncertainty Under the hybrid probabilistic PoF-based fatigue life prediction framework, a white-box approach for modeling total uncertainty, including physical uncertainty, statistical uncertainty and model uncertainty, was developed for LCF life prediction based on Bayesian information updating. In addition, the black-box approach was expanded to quantify the model uncertainty in LCF life prediction. Compared with the white-box approach, there is no consideration of the uncertainties associated with the inner workings of the model in the black-box approach. The development of white-box approach, the improvement of methodology and expanding of research on black-box approach provided reliable theoretical basis and scientific method for model selection and comparison. The proposed probabilistic PoF-based fatigue life prediction methodology intrinsically explains the scatter of service life of complex structures subjected to the same conditions and has certain conductive significance for structural health monitoring, design, safety evaluation and remaining life assessment of major mechanical equipments.更多还原