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Fractal models of rock micro-fractures
Published in Xie Heping, Fractals in Rock Mechanics, 2020
The fracture profiles of intergranular and transgranular fractures are often found on fracture surfaces of a rock. Local stress concentrations at micro-voids, micro-cracks, and inclusions etc. are the causes of transgranular fracture. Generally, the fracture will be intergranular because less energy is needed. Hence, a fracture surface of rock is that of combined transgranular and intergranular fracture as shown in Photo 13.4. Its fractal model is pictured in Figure 13.3, N=5;r=1/3.605;D=log(5)/log(3.605)=1.255. Its critical crack extension force becomes Gcrit=(3.605)0.255×2rs=1.38×2rs. The analytical results and measured values are listed in Table 13.1. It is clear that calculated results are in good agreement with measured ones. The reason why the intergranular brittle fracture and the combining fracture forms take place more easily for the same grain size can be seen quantitatively in Table 13.1.
Effects of flake-shape and content of nano-mullite on mechanical properties and fracture process of corundum composite ceramics
Published in Journal of Asian Ceramic Societies, 2021
Wei Lian, Yan Liu, Wenjie Wang, Yangtao Dong, Sheng Wang, Rui Zhu, Nan Xie, Yueqin Wang, Zhenying Liu, Yin Liu, Ling Bing Kong
Coal gangue can be used to prepare flake nano-mullite using molten salt method. Both the difference in particle size of the mullite and alumina and the content of mullite showed significant influence on microstructure and mechanical properties of the corundum composite ceramics. Specifically, the sample MTA25 has the highest relative density and lowest apparent porosity after sintering at 1550°C. Accordingly, the sample exhibited a flexural strength 263.7 MPa and a fracture toughness of 5.0 MPa·m1/2, which are higher than the reported data. The enhancement in the mechanical strength is mainly attributed to the dominance of transgranular fracture of the materials, in which the energy of destruction can be effectively consumed. According to Griffith fracture theory, it is found that MTA25 sintered at 1550°C has largest critical crack size and highest fracture work, which are 173.9 μm and 127.6 J/m2, respectively.