Construction of nano/micro fracture mechanics

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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.