A nonlinear strength criterion for rock- like materials is developed in this paper. Taking α as an angle of micro- failure orientation in rock- like materials, a formulation between α and load is derived from a mixed- mode fracture criterion based on linear elastic fracture mechanics. According to micro- failure experimental phenomena of rock- like materials, a failure characteristic parameter under triaxial compression condition is chosen, which is relevant to confining pressure and is an invariant. A theoretical nonlinear strength criterion is also derived, which is exactly in the same mathematical form as the original Hoek- Brown empirical strength criterion. In addition, it is also found that the coefficient m in the Hoek- Brown criterion has physical meaning which is related to the ratio between the uniaxial compressive strength and the uniaxial tensile strength.

Scanning electronic microscopy(SEM) was employed to investigate fractographs of sandstone in mine roof strata under thermal- mechanical coupled effect. Based on the evolution of sandstone surface morphology in the failure process and fractography, the fracture mechanism was studied and classified under meso and micro scales, respectively. The differences between fractographs under different temperatures were examined in detail. Under high temperature, fatigue fracture and plastic deformation occurred in the fracture surface. Therefore, the temperature was manifested by these phenomena to influence strongly on micro failure mechanism of sandstone. In addition, the failure mechanism would transit from brittle failure mechanism at low temperature to coupled brittle- ductile failure mechanism at high temperature. The variation of sandstone strength under different temperature can be attributed to the occurrence of plastic deformation, fatigue fracture, and microcracking. The fatigue striations in the fracture surfaces under high temperature may be interpreted as micro fold. And the coupled effect of temperature and tensile stress may be another formation mechanism of micro fold in geology.

Whether or not the surface morphologies of conducting polythiophene films with nanotubular structure having a fractal characteristic was investigated based on the scanning electrical microcopy(SEM) images with self- organized nanostructure. Fractal results indicated to be valued in the quantitative characterization of the surface morphologies of electrochemically synthesized polythiophene films. The fractal characterization of surface morphology depended mainly on the grizzly threshold on these SEM images. The relationship between the threshold and the fractal dimensionality can be expressed as a function. Therefore, the fractal dimensionality of surface morphology and nanostructure of these films might relate to the mechanical properties/ behaviors or their electrochemically synthesized process. The fractal dimensionality was also illuminated from the physical point of view based on a binary image analysis. In addition, the effect factors and similarity rule of fractal dimensionality in those SEM images analyzers were discussed. The critical value to affect the determining fractal dimensionality was obtained.

砂岩的热开裂研究具有广泛的工程背景，本文实时在线观察和研究了不同温度作用下平顶山砂岩的热开裂：温度低于150℃时，砂岩几乎不发生热开裂；温度从150℃升高到300℃过程中大量的热开裂发生，而不同的矿物成分发生热开裂的阈值温度不完全相同，因此热开裂的阈值温度或者阈值温度范围只具有统计意义。砂岩热开裂主要与矿物成分的热学与力学性质有关，除了受到矿物热膨胀不匹配及热膨胀各向异性的影响，更重要的还受到矿物颗粒形状的影响，如热开裂多发生在矿物颗粒的短轴方向、优势结晶取向、颗粒奇异界面等，且热开裂的分布具有随机性。实验还观察到砂岩表面微缺陷发生闭合的全过程，在冷却过程也有微裂纹形成等现象。