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

基本信息

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

项目摘要

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. 考虑陶瓷中随机微观结构的强度特性分析：导出应力强度因子的修正因子作为随机系统中的新力学参数，以便在该参数中反映陶瓷中微观结构的影响。为了评估修正系数，通过考虑由于微观结构的差异而导致的单个晶粒的刚度和尺寸的变化，对裂纹尖端应力场进行了数值分析。应力场受裂纹尖端晶粒周围晶粒刚度的显着影响，但几乎不受晶粒尺寸的影响。发现从上述分析获得的修正因子随着裂纹长度的增加而变小。使用修正因子的模拟分布，根据使用阻力曲线概念的标准来估计强度分布。估计的强度分布在实验结果中能够很好地表现出平均趋势。 2．考虑金属材料中随机微观结构的疲劳特性分析：采用变形六边形作为金属多晶材料建模的元素。在建模具有两相的微观结构时，使用随机数从元素中选择相，使得选择应与微观结构中各相所占的比例相对应。对于由这些元素组成的多晶材料，基于引发裂纹的连接模式和单个裂纹的扩展模式之间的竞争，构建了裂纹扩展模型。利用该模型，采用蒙特卡罗程序对四种不同微观结构金属材料的缺口部件在多轴疲劳下进行了统计模拟。结果表明，模拟寿命的分布范围足以覆盖实验观察到的失效寿命。