金属结构疲劳载荷谱顺序效应的损伤力学机理与概率特性研究

This proposal is to develop continum damage mechanics approach for integrating mechanical damage model into probabilistic performance analysis, in virtue of its unitized capability to deal with fatigue damage formation and crack growth. Aiming at the fatigue progressive failure process of metallic components exposed to complicated loading spectrum for extensive engineering applcation, this proposal intends to search for the fatigue damage mechnical model allowing for complicaited mechnical effects with substantial micro-scale metalligical backgrounds. Also some theoretical and technical puzzles will be overcome, such as the effecitveness of small size and large scale numerical computation, the statistical compatibility between numerical test samples and objective physical population, and the adaptive control of numerical sampling capacity, as well. Under the support of physically fatigue failure test verification with modest sampling size, this research will explore to understand and cognize the applying sequecial effect, mechnical mechanism and probabilistic statistical behavior of a complicated structural component applied by a random loading spectrum occured in real engineering circumstance. This research will realize such a technical ability and means to carry out an integrated analysis for the mechnical failure and statistical performance of an arbitrarily shaped metallic component with complicated dangerous locations applied by multi-axial stresses, all of which only require fudamental data from material and simple element-level fatigue tests, and also this dual power cannot be obtained through the current technical methods and means. From perspective of engineering, this proposal also is to explore an effective methodological pathway required in engineering design, analysis and test technologies, for instance, to predict the safety of structural service, and simplify a tedious loading spectrum with more reliability.

本项目发展具备疲劳损伤形成与裂纹扩展统一分析能力的连续介质损伤力学方法，实现损伤力学与概率统计分析方法的有机结合。针对工程中广泛使用的金属结构在疲劳载荷谱作用下的损伤渐进破坏过程，开展较大子样的元件级疲劳试验，通过微观断口观察及理论研究，建立具有微观冶金物理支持并能计及载荷谱顺序效应的疲劳损伤力学模型；在概率化疲劳损伤力学模型基础上，解决好小尺度大规模数值计算效率问题、数值"试验"样本与客观物理的概率统计特性相容性问题以及数值样本的自适应控制问题。设计恰当的疲劳载荷谱，从物理试验与数值计算两方面开展典型金属构件载荷谱作用顺序效应的力学损伤及其概率统计特性研究，充分验证损伤力学模型及其概率统计特性的有效性。从而实现仅在简单元件级疲劳性能试验基础上，解决复杂结构疲劳载荷谱作用下的疲劳损伤形成与扩展的渐进破坏分析与概率特性估计问题。

利用双尺度夹杂理论，建立了能计及复杂力学效应（包括压应力）的疲劳损伤累积力学模型，解决了疲劳损伤力学模型在复杂结构件数值计算中的效率问题，形成了能计及高/低周双尺度疲劳损伤演化的高效数值计算手段。主要研究工作有：其一，提出了等向强化与随动强化非比例混合的细观应力应变循环滞回环构造方法，编制了宏细观桥联非线性方程组计算程序，使在宏观循环应力比R= 0.5以下，均能很好建立其循环滞回曲线；其二，提出了损伤因子连续变化的概念，解决了复杂载荷谱在双尺度损伤估算下的理论难题；其三，改进了现有疲劳损伤累积力学模型的构造形式，在塑性应变增量上增加了可计及不同循环比的非线性指数项，使复杂载荷谱的疲劳寿命估算能力得到很大改善。.提炼了常规疲劳损伤力学模型中各物理量的定义，建立了由单次试验数据对模型内变量计算的数值优化反演算法及模型算法设计，并基于概率多项式的NIPC展开方法，解决了数值结果与试验数据的概率统计相容性问题，并基于Nataf非独立变量抽样方法，完整实现了概率化疲劳损伤力学模型的概率数值抽样。.运用宏细观双尺度的联络方程及循环应力应变曲线构造方法，实现了高低载对疲劳损伤的影响效应，定量了疲劳载荷谱顺序效应的损伤力学机理与其概率特性。不仅为处理工程技术问题奠定坚实的力学基础，并初步形成了可工程使用的高精度疲劳寿命估算新方法。.本项目在理论研究上取得了四个方面的创新性突破，其一，提出了等向强化与随动强化非比例混合的细观应力应变循环滞回环构造方法可很好建细观循环滞回曲线；其二，提出了损伤因子连续变化的概念，解决了复杂载荷谱在双尺度损伤估算下的理论难题；其三，改进了现有疲劳损伤累积力学模型的构造形式，在塑性应变增量上增加了可计及不同循环比的非线性指数项，使复杂载荷谱的疲劳寿命估算能力得到很大改善；其四，利用试验数据、数值反演以及概率抽样方法，建立了较完备的疲劳损伤（寿命）概率分布特性构造方法。