Development of a Damage-Fracture Simulation System for Stregth and Life-Time Evaluation of Structures

本项目旨在发展一种系统的、统一的计算技术，利用连续损伤力学(CDM)和有限元方法(FE)来预测结构单元的断裂和寿命。通过用断裂有限元的集合来模拟裂纹，可以分析损伤、裂纹扩展和最终断裂的全过程。本课题的主要研究成果如下：1.将损伤演化方程和非弹性本构方程引入商用有限元程序，用断裂有限元的集合体模拟裂纹，建立了损伤断裂过程的模拟系统。为了建立高温下构件蠕变裂纹扩展机制，讨论了数值计算结果与网格相关的原因。阐明了损伤演化方程的应力敏感性和前一损伤场应力敏感性对裂纹尖端应力奇异性的影响。利用SA508核反应堆压力容器钢的试验结果，建立了疲劳损伤演化方程，分析了缺口试件的疲劳损伤过程。为了建立更加系统的损伤演化方程框架，在Gibbs热力学势能的基础上发展了弹塑性损伤理论。通过分析前向损伤场对裂纹尖端应力奇异性的影响，讨论了裂纹尖端应力场无奇异性的条件。这一分析解释了基于CDM和有限元的损伤和断裂模拟方法中观察到的网格依赖的数学结构。

The present project aims at the development of a systematic and unified computational technique for fracture and life-time prediction of structural elements by means of Continuum Damage Mechanics (CDM) and Finite Element Method (FEM). By simulating a crack by an aggregate of fractured finite elements, the whole process of damage, crack growth and final fracture can be analyzed. The major results of the present project are summarized as follows :1. A simulation system of damage and fracture process was developed by incorporating damage evolution equation and inelastic constitutive equations into commercial Finite Element Program and by modeling a crack by an aggregate of fractured finite elements.2. In order to establish a system of creep crack growth in structural components at elevated temperature, the causes of mesh-dependence of the numerical results are discussed. The effects of stress sensitivity of the damage evolution equation and those of the preceding damage field on the stress singularity at the crack-tip were elucidated.3. A damage evolution equation for fatigue was formulated by the use of the experimental results of SA508 pressure vessel steel for nuclear reactors, and a fatigue damaged process of notched specimens was analyzed.4. In order to establish a more systematic framework of damage evolution equations, an elastic-plastic-damage theory was developed on the basis of Gibbs thermodynamic potential.5. By analyzing the effect of the preceding damage field on the stress singularity at a crack-tip, the condition for the crack-tip stress field to be non-singular was discussed. This analysis elucidated the mathematical structure of the mesh-dependence observed in the damage and fracture simulation method based on CDM and FEM.