Methods of Inspection and Quantitative Evaluation of Creep-Fatigue Small Cracks at Elevated Temperature

1.为研究热疲劳裂纹扩展行为，进行了变温疲劳裂纹扩展试验和应力松弛条件下的蠕变裂纹扩展试验。从基于非线性断裂力学的两类裂纹扩展方程出发，推导出两种类型的高温低周疲劳寿命定律。用高灵敏度电位法验证了裂纹扩展过程中蠕变-疲劳交互作用的机理和机理。利用木质金属板和几种形状的玻璃裂纹，得到了表面裂纹尺寸与电位降之间的关系。利用图像分析技术对304不锈钢表面小裂纹的数量和长度进行了测量，并用高温显微镜连续观察了蠕变疲劳试验过程中小裂纹的萌生和早期扩展行为。在此基础上，建立了蠕变和蠕变疲劳过程中裂纹萌生和扩展的随机模型。为了处理微观结构不均匀引起的小裂纹萌生时间和扩展速率的离散性，在模型中使用了随机变量技术。采用蒙特卡罗方法进行了数值模拟。

1. Fot the purpose of investigating the crack propagation behavior in thermal fatigue, crack propagation tests of varying temperature fatigue and of creep under stress relaxation conditions were conducted.2. Two types of LCF life laws were derived from the two types of crack propagation equations based on nonlinear fracture mechanics at elevated temperature.3. The mechanism and mechanics of creep-fatigue interaction in the crack propagation process were verified using high-sensitivity electric potential methods.4. Relationships between surface crack dimension and electric potential drop were obtained using wood metal plates and glass-made cracks of several kinds of shape.5. Measurements of the number and the length of small surface cracks of 304 stainless steel were done by means of image analysis, and the behavior of small crack initiation and early growth were observed continuously during creep-fatigue tests with a thigh-temperature microscope.6. Based on the above results, stochastic models of crack initiaction adn propagation in creep and creep-fatigue were developed. In order to deal with the scatter of small crack initiation time and propagation rate caused by microstructural inhomogeneity, a random variable technic was used in the models. Numerical simulation was conducted by Monte Carlo method.