三维广布疲劳损伤扩展的多裂纹Sm-XFEM计算方法和试验研究

广布疲劳损伤是航空结构中的典型损伤形式，对飞机结构完整性构成严重威胁。本项目以飞机结构中存在的广布疲劳损伤问题为背景，拟建立一套较完整的以多裂纹Sm-XFEM计算为主、试验为辅的分析方法，研究多裂纹之间的扩展机理和扩展规律，为航空航天领域内复杂结构的耐久性/损伤容限设计提供理论基础与技术支撑。具体研究工作包括：在课题组针对S-FEM方法、XFEM方法研究和自编分析软件的基础上，开展任意多裂纹的二维和三维Sm-XFEM算法理论研究；开展基于Sm-XFEM的裂纹扩展方法研究，发展一种自动模拟三维广布损伤扩展路径的新方法，实现任意数目和曲面形状的三维广布疲劳损伤扩展仿真；开展三维广布疲劳损伤扩展试验研究，揭示三维广布损伤扩展、连通和破坏的机理，验证算法及其软件的有效性；基于试验和数值分析，研究几何、材料、裂纹位置和形貌等因素对多裂纹扩展的影响规律。

Widespread fatigue damage (WFD) has been one of the most representative damages styles in the aircraft structures, which has badly threatened the structures integrality of aircraft. This proposal comes from the WFD in the old aircraft. The objective of this project is to setup a platform to evaluate life concepts prior to expensive testing programs, and the global research focus is on developing efficient simulation tools, particularly using the Sm-XFEM (The Smoothed Extended Finite Element Method). Through numerical modeling with experimental testing, a better understanding of the propagation behavior of the WFD can be gained and thus lead to providing the theory and technique for the applications of the three-dimensional damage tolerance and durability.. The Sm-XFEM for arbitrary multiple cracks has been presented on the basis of our self-developed S-FEM (Smoothed Finite Element Method) and XFEM (Extended Finite Element Method) codes. The linear elastic fracture mechanics based on Sm-XFEM is proposed, and then a new automatic method for simulating crack propagation path is acquired by considering the characteristics of Sm-XFEM. Arbitrary crack propagation is simulated by using this method. Furthermore, the experiments about three-dimensional WFD propagation are investigated, in order to finding the mechanism of three-dimensional WFD propagation, coalescence and fracture. At the same time, the effect of the Sm-XFEM code on simulation the propagation of WFD will be validated by the corresponding WFD tests. Finally, the necessary conditions on the propagation of WFD are certificated for various geometry parameters, materials, location and shape ratios of cracks on the basis of the experiments and numerical simulation.