Experimental Study On Nanoindentation Tests Of Granite After High-temperature Heating Treatment

The macroscopic mechanical properties of rock always exist in a profound microscopic mechanism.In this dissertation,the mechanical properties and microstructural characteristics of granite after high-temperature heating treatment were studied microscopically by theoretical analysis and experimental study.The change laws of mineral composition,surface morphology and mechanical properties of the granites with the change of temperature were analyzed by X-ray diffraction experiments,microscopic observation and nanoindentation tests of the granites after high-temperature heating treatment.The overall mechanical properties of the granites after different high temperatures were obtained by homogenization analysis,and the differences of its change laws from those obtained by traditional mechanics experiments were also analyzed.The main conclusions are as follows:(1)The chlorite minerals disappear at 600°C and above.Quartz,potash feldspar and albite almost do not change,and their contents are almost consistent with those before the heating treatment.Mica would loss water when the heating treatment temperature is relatively high.(2)The color of granites shaded,the distribution of black components on the surface decreased and the overall samples gradually displayed pale yellow.The more the temperature was,the more the mass reduced,the more obvious micropores increased,and the weaker the bond between grains behaved.(3)Microcracks appear on the microscopic surface of the granites after high temperature,and the number and width of the cracks increase with the rise of the temperature.The uniform gloss of the mica minerals decreases gradually with the increase of heating temperature,and becomes dark,even cracks emerge.When at300? and higher temperature,the rugged dark black area appears obvious brown material.(4)The elastic modulus and hardness of each mineral component show similar statistical distribution and variation as the heating treatment temperature changes.The elastic modulus of quartz decreases with the increase of temperature,and the decrease is large.The elastic modulus distribution after high temperature is more concentrated and the distribution range is smaller.The elastic modulus of the quartz decreases sharply from 500? to 600?,because the crystal structure changes from ? phase to ?phase near 573?,and the physical mechanical properties of quartz are obviously changed.The elastic modulus of feldspar decreases with the increase of temperature,the decrease is smaller,and its elastic modulus distribution range after different temperature is larger.The elastic modulus of mica increases gradually with the increase of temperature,and its distribution range is also large.(5)The homogeneous elastic modulus of the granites fluctuates with the heating temperature,and its overall trend is decreasing within small amplitude.The variationof Poisson's ratio of the granites after different temperature is very small,and no obvious change rule was observed.In the homogenization model,the changes that the granite structure becomes loose and the intergranular cementation weakens after high temperature have not been reflected,and the more to reflect is the comprehensive changes in mineral mechanics.Evaluating the mechanical properties of materials at room temperature by homogenization method still has important engineering practical significance.But it needs to be further optimized for suitable application for the analysis of the mechanical properties of rock after high temperature.