Construction of nano/micro fracture mechanics

为了从原子势的微观特征和临界分解剪应力的细观特征来评价断裂韧性的宏观特征，提出了分子动力学与裂纹尖端离散位错分布方法相结合的方法。并将该方法应用于W和NaCl单晶的断裂韧性分析，结果表明，该方法可以从细观和细观特征上定量地估计其韧脆转变，且强度准则非常简单，控制裂纹尖端微尺度边界条件的细观特征非常重要。为此，开发了现场观测系统，对其特性进行实验评价。利用该系统，阐明了条纹形成的机理。基于这一机理，疲劳极限特性的评价方法是从细观特性发展而来的。即，该方法可以评价非金属夹杂物和表面粗糙度的影响。该方法采用夹杂物和表面形态的统计表达式、材料细观性能的统计表达式以及微缺口和裂纹对疲劳极限影响的定量表达式。将预测值与实验值进行了比较，结果表明该方法对材料的强度计算是有效的。

A method of combined method between the molecular dynamics and the discrete dislocation distribution method in the crack tip has been proposed in order to evaluate the macro characteristics of fracture toughness from micro characteristics of atomistic potential and the meso characteristics of critical resolved shear stress. And the method has been applied to the fracture toughness of the single crystal of W and NaCl, and it has been found from the results that the present method can estimate the ductile-brittle transition quantitatively from the micro and meso charactestics and moreover the strength criteria is very simple, the meso characteristics which control the micro-scale boundary condition of crack tip is very important. Therefore the in-situ observation system has been developed in order to evaluate the characteristics experimentally. Using this system, the mechanism of striation formation has been clarified. Based the mechanism, the evaluation method for fatigue limit characteristics has developed from the meso-characteristics. Namely, the method means that which can evaluate the influence of non-metallic inclusion and surface roughness. In the method, the statistic expression of the inclusion and surface configuration, the statistic expression of meso-scale material properties, and the quantitative expression for influence of micro notch and crack on fatigue limit are used. As the results of comparison between the predicted value and experimental one, it has been found that the proposed method is valid for the strength of materials.