DAMAGE MECHANICS APPROACH TO LIFE PREDICTION AND DAMAGE ANALYSIS OF HIGH TEMPERATURE COMPONENTS

本项目致力于开发一种基于损伤力学的有效和合理的高温构件寿命预测和损伤分析方法。1.作为损伤力学最基本的问题，首先讨论了材料损伤的力学模型。结果表明，各向异性损伤的一般状态可以用二阶对称张量来描述。2.作为损伤力学在高温构件寿命预测中的一种应用，分析了多轴应力状态下蠕变裂纹的扩展，验证了该方法的有效性和实用性。3.材料的损伤会对其变形特性、刚度和断裂韧性产生影响。然而，对于蠕变的损伤和断裂，弹性模数的变化对其影响不大。4.损伤力学方法的特点是同时分析损伤过程和变形过程。因此，作为本项目的第二个目的，建立了实用有效的非弹性本构方程。5.在高温多轴应力条件下，对316不锈钢和改性9Cr-1Mo钢进行了蠕变、塑性和循环塑性试验，并建立了描述这些结果的新的统一本构方程。6.提出了描述温度变化历史和非比例加载路径影响的循环塑性本构方程。文中还讨论了这些方程对损伤材料的推广。

The present project is concerned with the development of an effective and rational approach to life prediction and damage analysis of high-temperature components on the basis of damage mechanics. The results of the project are summarized as follows: 1. As the most fundamental problems of damage mechanics, mechanical modelling of material damage was discussed first. It was shown that a general state of anisotropic damage can be described by a second rank symmetric tensor. 2. As an application of damage mechanics to the life prediction of high temperature components, creep crack growth under multiaxial state of stress was analyzed, and the effectiveness and utility of this method was ascertained. 3. Damage of materials may have influence on their deformation characteristics, rigidity and fracture toughness. However, as regards damage and fracture of creep, the influence of the change of elasticity modulus was insignificant. 4. The characteristic aspect of the damage mechanics approach is the simultaneous analysis of damage process and deformation process. Thus, as the second purpose of the present project, practical and effective constitutive equations of inelasticity were developed. 5. For this purpose, creep, plasticity and cyclic plasticity tests were performed for type 316 stainless steel and modified 9Cr-1Mo steel under high temperature multiaxial stress condition, and a new unified constitutive equation to describe these results was developed. 6. Constitutive equations of cyclic plasticity were also proposed to describe the effects of the history of temperature change and that of non-proportional loading path. Extension of these equations to damage materials was also discussed.