【作者】 肖建清；

【导师】 丁德馨；

【作者基本信息】 中南大学 ， 工程力学， 2009， 博士

【摘要】 工程中的岩体不仅仅承受着静态荷载的作用,还经受着爆炸、冲击、地震等动态荷载的影响。因此,研究循环荷载作用下岩石的疲劳特性,提出稳定性分析方法和控制手段是工程中迫切需要解决的问题。特别是近年来,由于大规模水利工程的建设,城市地下交通的普及,大跨度超长隧道的开挖,以及深部矿藏的开采,许多前所未有的动力学难题摆在了我们的面前。如何优化隧道、巷道、边坡、水坝、基岩等结构的抗震性能,保障工程安全以及人类的生命安全,这些都是科研工作者的历史使命,也是我们抓住机遇,施展才能的大好平台。本文围绕着结构疲劳分析的基本框架,着重从理论研究和实验分析两大方面进行了一系列开创性的研究,同时给出了工程应用的框架雏形,具体包括以下几个方面的内容:(1)针对于三峰谷雨流计数模型的不足之处,提出了改进方案。改进后的三峰谷计数模型融等值点压缩、峰谷检测以及循环计数为一体,极大地简化了计数过程。运用改进三峰谷计数模型,对现场采集的爆破振动应力谱进行了循环计数,统计结果表明,单次爆破中小幅疲劳循环占绝大部分,而且拉压循环所占的比例比较大。(2)根据岩石损伤演化具有三阶段发展规律的这一特点,提出了倒S非线性疲劳累积损伤模型。探讨了倒S模型中参数的物理含义以及对倒S曲线的影响,给出了参数的建议取值范围。运用倒S模型,演示了岩石三级加载时累积损伤的计算,首次提出了疲劳路径的概念,从理论上解释了“锻炼”效应产生的根本原因。由于倒S模型考虑了疲劳初始损伤,考虑了加载次序对累积损伤的影响以及荷载间的相互作用,因此具有较高的精度。而且,利用疲劳路径的概念,倒S模型可以直接用于随机疲劳加载时的损伤计算和寿命估算。(3)针对倒S模型参数估计问题,提出了以有限组合法计算初始值,再应用Levenberg-Marquardt法进行倒S曲线拟合的解决方案。计算结果表明,此方案拟合得到的倒S曲线与实验数据均为高度相关,既说明了拟合算法的高效性,也说明了倒S模型的正确性。(4)分析了加载条件对岩石全应力应变曲线的影响,给出了静载强度确定的原则。从试验的角度,讨论了应力上限、应力幅值、加载波形以及加载频率对岩石疲劳强度的影响。试验结果表明,上限应力越高,应力幅值越大,加载频率越高,岩石的疲劳寿命就越短。对于加载波形的影响,试验结果表明,正弦波加载的疲劳寿命大于三角波加载的而小于矩形波加载的。(5)研究了岩石疲劳变形的特性,验证了疲劳破坏的极限变形规律。分析了轴向变形、横向变形和体积变形在疲劳加载过程中的演化规律。首次得出了以下结论:三种变形都具有三阶段演化规律,三阶段的划分基本一致,横向变形和体积变形的增量比轴向变形的大得多。(6)依据试验结果,对比了各种损伤变量定义法的合理性,指出残余应变法由于物理意义明确,考虑了初始损伤,是一种相对比较理想的定义方法。岩石的损伤演化具有三阶段规律,而影响损伤发展的主要因素有应力水平以及初始损伤等。分析结果表明,上限应力、幅值及初始损伤越高,损伤演化曲线的第三阶段占疲劳寿命的比例越大,第二阶段所占比例相应减小,岩石的疲劳寿命也就越短。(7)将名义应力法中材料疲劳性能描述的S—N曲线以及作者提出的倒S模型,融入到局部应力应变法中,形成了一种适用于岩石材料的修正局部应力应变法。以倒S模型为基础,演示了变幅加载条件下残余寿命及总寿命的估算步骤。根据修正局部应力应变法的原理,简要介绍了随机疲劳加载条件下疲劳寿命估算的一般步骤。(8)根据疲劳分析的特点以及疲劳软件开发的需求,提出以插件式软件体系结构构建开放式疲劳分析环境的新思路。针对于插件系统运行效率的问题,提出了建立插件映射表,利用动态加载技术节省系统运行开销的解决方案。同时,为了解决插件标识中的重名现象,提出了由宿主程序动态分配ID的方案,杜绝了重名的风险,降低了系统与插件间的耦合度。更多还原

【Abstract】 Rock mass in engineering is not only subjected to static load but also affected by dynamic load such as blasting, impact and earthquake etc. Thus, it is a crucial problem to solve in engineering that taking research on the fatigue behavior of rock subjected to cyclic loading and putting forward analyzing and controlling methods for stability. Especially in the last years, with the development of large-scale hydraulic engineering, urban underground transportation engineering, large-span and large-distance tunnels engineering and deep mining engineering, there are many dynamic problems for us.A series of innovative investigations are carried out in theory、experiment and engineering in this paper based on the frame of fatigue analysis of structure. The main contents include:(1) An improved scheme is proposed to overcome the defects of three-points rain flow counting model. The improved model simplified the process of counting by integrating equivalent points compression, peak-valley points detection into cycle counting. Then, the distribution of frequency is obtained by using the improved model to analyze the stress spectrum of vibration. The statistical result indicates that most of fatigue cycles are low amplitude cycles and the proportion of tensile and compressive cycles is very high.(2) A lot of experiments indicate that the axial irreversible deformation of rock subjected to cyclic loading has stable value and three-phases development law. Base on which, a new inverted-S shaped nonlinear fatigue damage cumulative model is presented in this paper. These physical meanings and ranges of all Parameters of this model are discussed. By using this model, a damage calculation process of rock under three-level cyclic loading is demonstrated and a concept of fatigue path is put forward. To our surprise, the basic reason contributing to the fatigue "training" effect can be well explained theoretically by the concept of fatigue path. In sum, this model has relatively higher accuracy by considering the initial damage of material, loads interaction effect and loading sequence effect and can be applied in damage calculation and fatigue life prediction of random or variable amplitude cyclic loading.(3) A Finite Combination Method is proposed in this paper to estimate initial parameters for Levenberg-Marquardt calculation. That is, initial points uniformly distributed in the feasible region of parameters are inputted for Levenberg-Marquardt calculation and those parameters with minimum residual sum of squares are taken as final initial parameters. The fitting result is highly correlated with experimental data, by which this new method is improved effective and the inverted-S model correct.(4) The principle determining the static strength of rock is put forward after taking an analysis about the influence of loading condition on the complete stress-strain curve. Then, the influence of maximum cycling stress, loading amplitude, waveform and frequency on fatigue strength has also been studied. The experimental results show that the rock has a shorter life when being applied higher maximum cycling stress and amplitude or higher loading frequency. Meanwhile, an obvious conclusion can be drawn that the life of rock under sine waveform is bigger than that under triangle waveform but smaller than that under rectangle waveform.(5) The deformation properties of rock is studied and the law of ultimate deformation is verified in this paper. The investigation on evolution law of axial, lateral and volumetric strain shows that a three-phases developing law can be found in these three kinds of strains and the developing curves can be divided into same three phases. Furthermore, an innovative conclusion can be reached that the deformation and deformation rate of lateral and volumetric strain are much larger than those of axial strain.(6) The experimental result of rock indicates that many methods such as elastic modulus method, ultrasonic velocity method, ultimate strain and residual strain methods are all able to represent the damage evolution law of rock. Among them, residual strain method is more suitable for its clear concept and consideration of fatigue initial damage. The damage of rock develops according to three-phases law and the main factors affecting fatigue deformation include stress level and initial damage. The result shows that the higher maximum stress, amplitude and initial damage, the shorter fatigue life for the increase of proportion of the third phase in the whole life.(7) A Modified Local Strain Method applicable for rock is presented by introducing S-N curve and the inverted-S model proposed by author. Then, the approach to residual life and total life estimation is illustrated based on the inverted-S model. Meanwhile, according to the principle of the Modified Local Stain Method, the general steps of estimating fatigue life of rock subjected to random loading are briefly introduced.(8) A new idea of using Plug-in software architecture to construct fatigue analysis system is put forward after comprehensive research on the procedure of fatigue analysis of structure and the requirement of fatigue software development. Then, a solution to saving the cost of system running is proposed by constructing a plug-ins mapping table and using dynamic loading technique. Meanwhile, a method of dynamically allocating symbol IDs for plug-ins by host program is brought forward to put an end to name repeating phenomenon. This method also reduces the coupling degree between host program and plug-ins.更多还原