延性材料与裂纹构元的断裂理论及毫微测试方法研究

Fracture toughness assessment of three dimensional (3D) structural crack is an important part of the safety assurance of key components applied in nuclear power, chemical industry, aerospace and petroleum engineering. Previous problems, such as the analytical representation of elastic plastic deformation of structural components, the theory of critical fracture strength and the law of crack tip constraint have not been solved yet. There is still a big gap between the predominant method of simplifying crack problem and the requirement in high-level structural integrity assessments. This project aims to achieve the theoretical assessment of fracture behaviors of 3D structural cracks and innovative testing with three approaches. The first is to get the theoretical representation of elasto-plastic deformation of typical structural components and the semi-analytical stress fields of 3D crack tip containing the characteristic constraints based on energy equivalence method, followed by creating the test methods for fracture toughness and the evaluation of constraint effect on 3D structural cracks. The second is to establish the fracture criteria of ductile materials by analyzing critical fracture of structural components with different constraint levels based on full-range constitutive relationship and then implement the theoretical prediction of fracture toughness of 3D structural cracks with different constraint levels in conjunction with semi-analytical 3D crack tip stress fields. Finally, these two approaches mentioned above would be combined to develop a set of miniature test methods for fracture toughness of in-service materials and small-sized components. The expected achievements would provide the basic support on theory and test technique of integrity assessment for structures containing defects, which have important theoretical significance and engineering application prospects.

三维结构裂纹断裂韧性的评价是保障核电、化工、航空航天、油气等工程中的关键零部件安全服役的重要内容，与此相关的构元弹塑性变形解析表征、临界断裂强度理论、裂尖约束规律等历史性难题尚未突破，工程上广泛采用的裂纹问题简化处理方式距精细分析的结构完整性高级别评估有很大差距。本项目拟按三方面实现三维结构裂纹断裂行为的理论评价和测试创新，一是基于能量等效原理对典型构元弹塑性行为实现解析表征并得到包含约束特性的半解析三维裂尖应力场，进而建立结构裂纹断裂韧性测试新方法和三维约束效应评价方法；二是基于全程本构关系对不同约束构元进行临界破断分析建立延性材料断裂准则，结合半解析的三维裂尖应力场，实现不同约束三维结构裂纹的断裂韧性理论预测；最后，结合该两种途径发展一套用于测试服役结构材料和小尺寸零部件断裂韧性的毫微测试方法。预计成果为裂纹结构完整性评估提供理论与测试方法的基础支撑，具有重要的理论意义和工程应用价值。

结构完整性评价是保障核电、化工、航空航天、油气等工程中的关键零部件安全服役的重要技术手段，延性材料与裂纹构元的断裂理论及毫微测试方法对结构完整性评价有重要意义。本项目从三方面研究了含裂纹结构的断裂行为预测方法及延性材料力学性能的毫微测试方法。一是基于能量密度等效原理对典型构元弹塑性行为实现了解析表征，得到了能量-载荷-位移关系、K因子、J积分和约束相关的裂尖应力场等重要信息的半解析表达式；二是基于全程本构关系对不同约束构元进行了临界破断分析，并建立了延性材料断裂准则，结合半解析的J积分和三维裂尖应力场，实现了不同约束三维结构裂纹的断裂韧性理论预测；三是提出了包含单轴本构关系、强度、硬度和循环本构关系等延性材料力学基本性能，以及残余应力的毫微测试方法。研究成果为结构完整性评价提供了理论与测试方法的基础支撑，具有重要的理论意义和工程应用价值。