Micromechanics for Random System and Its Application to Small Crack Problems

随机系统微观力学及其在小裂纹问题中的应用

• 批准号: 11650090
• 负责人: TOSHIHIKO Hoshide
• 金额: $ 0.7万
• 依托单位: KYOTO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2000
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11650090/
• 关键词: Random system; Micromechanics; Small crack; Microstructure; Crystalline orientation; Grain morphology; Fracture; Fatigue; 結晶粒径; 欠陥寸法; 多結晶材料; Random system; Micromechanics; Small crack; Microstructure; Crystalline orientation; Grain morphology; Fracture; Fatigue; 結晶粒径; 欠陥寸法; 多結晶材料

1. Analysis of Strength Characteristic by Considering Random Microstructure in Ceramics : The modification factor for the stress intensity factor was derived as a new mechanical parameter in a random system so that the influence of microstructures in ceramic could be reflected in the parameter. To evaluate the modification factor, numerical analyses on the crack-tip stress field were conducted by taking account of variations in the stiffness and size of individual grains as the difference of microstructures. The stress filed was significantly affected by the stiffness of grains around the grain at the crack-tip, but hardly influenced by the grain-size. The modification factor obtained from the aforementioned analyses was found to become smaller for a longer crack length. Using the simulated distribution of the modification factor, the strength distribution was estimated based on the criterion using the resistance curve concept. The estimated strength distribution was able to show an average tendency in experimental results well.2. Analysis of Fatigue Characteristic by Considering Random Microstructures in Metallic Materials : Deformed hexagons were adopted as elements in modeling metallic polycrys-talline materials. In modeling a microstructure with two phases, the phases were selected from elements by using random numbers so that the selection should correspond to the proportion of each phase occupied in the microstructure. For polycrystalline materials composed of such elements, a crack growth model was constructed based on the competition between the linkage mode of initiated cracks and by the propagation mode of an individual crack. Using the model, notched components for four kinds of metallic materials with different microstructures under multiaxial fatigue were statistically simulated by using a Monte Carlo procedure. It was shown that the distribution range of the simulated life sufficiently covered the failure life observed experimentally.

1。通过考虑陶瓷中的随机微观结构来分析强度特征：应力强度因子的修饰因子在随机系统中作为新的机械参数得出，因此微观结构在陶瓷中的影响可以反映在参数中。为了评估修饰因子，通过考虑到单个晶粒的刚度和大小作为微结构的差异，对裂纹尖端应力场进行了数值分析。所提出的应力受到裂纹尖端谷物周围谷物的刚度的显着影响，但几乎不受晶粒大小的影响。发现从上述分析获得的修饰因子在更长的裂纹长度方面变小。使用修饰因子的模拟分布，根据使用电阻曲线概念的标准估算强度分布。估计的强度分布能够很好地显示实验结果的平均趋势。2。通过考虑金属材料中的随机微观结构来分析疲劳特征：将变形的六角形作为对金属多晶材料进行建模的元素。在建模具有两个阶段的微结构时，使用随机数从元素中选择了相位，以便选择应与微结构中占据的每个阶段的比例相对应。对于由此类元素组成的多晶材料，根据启动裂纹的链接模式与单个裂纹的传播模式之间的竞争构建了裂纹生长模型。使用该模型，通过使用Monte Carlo程序在统计上模拟了在多轴疲劳下具有不同微结构的四种金属材料的缺口组件。结果表明，模拟寿命的分布范围充分覆盖了实验观察到的失败寿命。