大型复杂机械结构疲劳全寿命可靠性理论及方法研究

In order to improve and innovate the theory and method of reliability design and evaluation of large complex structures under complex load conditions with unstable load distribution, this project investigates the load flow between the structural parts in a mechanical system, and constructs TBM load spectrum; defines defect/damage state variable and achieve a unified representation of it in the total fatigue life period; reveal the competitive behavior and statistical dependence between different failure sites and different failure mechanisms; establishes fatigue reliability model of structural system; studies reliability allocation principles and reliability evaluation technique of complex structural system. These research works will solve the problems such as the current reliability allocation method is un-effective to large scale mechanical system, reliability design is hard to applied to complex mechanical part, complex load condition, and complex failure mechanism, and the accuracy of reliability evaluation is too low to effectively assess complex mechanical part reliability..Taking the large size complex structural part as a system containing a number of possible failure sites, establishes the relationship between service environment, system load, structural stress and stress at the critical site through rock breaking theory and refined structural dynamics finite element analysis. Using an innovative parameter of “micro crack group” represents the initial defect in the critical sites on a complex part. By converting the multiple stress - multiple strength interference relationship into a single load - multiple strength interference relationship, enable the accurate modeling of complex structural systems. Accurate reliability allocation will be accomplished based on dependent failure mechanism analysis and innovative mathematical expression. Based on multilevel statistical theory, develops reliability design model of components and systems, entirely reflecting the influence factors of structural reliability including multiple source uncertainty, multiple site damage and multiaxial stress.

针对载荷工况复杂、载荷分布非平稳的大型复杂结构可靠性设计与评估，研究结构系统载荷流，构建载荷谱；定义缺陷/损伤状态变量，实现全寿命阶段统一表征；揭示不同失效部位、不同失效机理之间的竞争关系和统计相关性，建立结构系统疲劳可靠性模型；探索复杂结构系统可靠性分配原理和评估技术，解决当前复杂系统可靠性分配难以实施、可靠性设计层次低、可靠性评估精度差等理论与方法问题。 .把大型结构部件作为含多个可能失效部位的系统，借助破岩原理和精细的结构动力学分析建立服役环境-系统载荷-结构受力-关键部位应力之间的联系；采用“微裂纹群”参量合理表征初始缺陷；将“多应力-多强度”干涉关系转换为“单载荷-多强度”干涉关系，使得复杂结构系统可靠性精确建模成为可能；基于相关失效机制和创新的数学表达实现精确的可靠性分配，基于多水平统计学原理建立可靠性设计模型，切实反映多源不确定性、多部位损伤、多轴应力等结构可靠性影响因素。

本项目以全断面硬岩掘进机（TBM）刀盘和主梁等大尺度复杂结构部件为对象，深入、系统地研究了机械结构部件（系统）疲劳可靠性设计、评估理论方法中的共性科学问题，取得了丰富的成果。.针对载荷工况复杂的TBM典型结构部件（刀盘、主梁）可靠性设计与评估涉及的载荷、应力、失效模式、失效判据，尤其是疲劳寿命预测方法和可靠性分配、可靠性评估方法等问题，采集、整理了大量TBM载荷数据，构建复杂岩层掘进载荷-时间历程，编制出了复杂工况下非平稳刀盘载荷谱。建立了TBM主机系统多尺度动力学模型，详细研究了TBM主传力结构载荷传递路径，获得了存在多结合面耦合作用的TBM主机系统主承力子结构间力流传递规律。.提出了初始缺陷等效裂纹方法和裂纹萌生与裂纹扩展两阶段分界方法，实现了结构疲劳全过程损伤参量的统一表征，实现了结构部件疲劳全寿命的断裂力学方法统一估算。.将多部位损伤复杂结构部件作为一个串联系统，揭示了结构部件上不同失效部位、不同失效机理之间的失效竞争关系及其统计相关性根源，建立了能全面反映载荷历程的不确定性和结构强度不确定性、融合结构静强度失效判据和疲劳失效判据的多元可靠性模型。建立的结构系统（串联系统）可靠性模型能客观、真实、准确的反映单元之间的失效相关性。同时，逆向应用全概率原理（贝叶斯概率法则），提出了能反映单元失效相关性的串联系统可靠性分配原理和方法，该方法把一个复杂的、存在单元失效相关性的系统可靠性分配问题，转化为多个简单的、单元独立失效的系统可靠性分配问题，成功突破了当前在工程实际中可靠性设计方法的应用困境，即对于存在单元失效相关性的系统（工程实际中的机械装备系统多为此类系统），高层次、系统级的可靠性设计难以实施（缺乏切实可行的系统可靠性分配方法）、低层次、零部件级的可靠性设计无所适从（无法准确建立系统可靠性需求与其对零部件可靠性要求之间的关系）。 .本项目成果对提高机械装备关键零部件可靠性设计水平和评估水平，以及提升装备可靠性有重要应用价值。