Damage Mechanics Approach to the Prediction of Deterioration and Fracture Process of High-Temperature Structural Materials

本项目的目的是开发一个本地的方法来进行高温结构部件的损伤和断裂分析的基础上连续损伤力学（CDM）和有限元法（FEM）。讨论了一种系统、统一的方法来模拟从损伤开始到裂纹扩展最终断裂的全过程。1）基于不可逆热力学本构理论，建立了一般加载条件下的损伤演化方程，为本文的研究奠定了理论基础。建立了多晶材料在多轴载荷作用下弹塑性损伤演化方程。建立了高温结构损伤与断裂过程精确分析的非弹性本构方程 ...更多信息 iscussed。阐述了比例和非比例循环加载下的硬化机制，并将其纳入循环塑性的非弹性本构方程中。3）讨论了基于CDM和FEM的局部损伤断裂分析方法的数值过程中存在的问题。分析表明，数值结果的网格依赖性不仅与裂纹尖端的应力奇异性有关，还与损伤演化方程的数学稳定性有关。4）为了避免裂纹扩展速率的网格依赖性，在引入理想塑性理论和裂纹尖端应力限制方法的基础上，提出了一种随机分布临界损伤值的方法。5）将所得损伤断裂分析的计算机算法应用于模拟高温下结构件中两圆孔蠕变裂纹扩展过程。在计算机上显示了结构单元全域的损伤和断裂过程。并与相应的实验观测结果进行了比较。少

The present project aims at the development of a local approach to damage and fracture analysis of high-temperature structural components based on Continuum Damage Mechanics (CDM) and Finite Element Method (FEM). A systematic and unified procedure to simulate the whole process ranging from the damage initiation to the final fracture due to crack growth was discussed. The major results of the present project are summarized follows :1) As a theoretical basis of the present approach, a systematic formulation of damage evolution equations under general condition of loading was developed on the basis of irreversible thermodynamic theory for constitutive theory. An evolution equation of elastic-plastic damage in polycrystalline materials under multiaxial state of loading was developed. The existence of damage surface and its evolution were discussed.2) Formulation of inelastic constitutive equations for the accurate analysis of damage and fracture process of high-temperature structures was d … More iscussed. The hardening mechanisms under proportional and non-proportional cyclic loading were elucidate, and were incorporated to formulate elaborate inelastic constitutive equations of cyclic plasticity.3) Problems intrinsic to the numerical procedure of the local approach to damage and fracture analysis based on CDM and FEM were discussed. It was elucidated that the causes of mesh-dependence of the numerical results consist not only in the stress singularity at the crack tips but also on the mathematical stability of the damage evolution equations.4) In order to avoid the mesh-dependence of crack growth rate, basides incorporation of perfect plasticity and a method of stress limitation at crack tips, a method of stochastic distribution of the critical damage values was proposed.5) The resulting computer algorithm of damage and fracture analysis was applied to simulate the process of creep crack growth from two circular holes in the structural element at high-temperature. Damage and fracture process in the whole domain of the structural element was displayd on the computer. Comparison with the corresponding experimental observation was also discussed. Less