高温作用后砂岩的孔隙分形特征与岩石本构模型研究

Study on pore fractal characteristics and rock constitutive model of sandstone after high temperature

基于砂岩的核磁共振与力学试验,结合孔隙结构分形理论,分析了高温对砂岩力学性能的双重影响,研究了孔隙分形维数与力学参数的内在机制.结果表明:在150~300℃范围内,力学性能被显著强化;当温度超过450℃后,力学性能将会被显著弱化.砂岩内部的中孔与大孔具有显著的分形特征,其分形维数与力学参数呈负相关,微孔不具有分形特征.构建了峰后应力跌落的分段式本构模型,提出了峰后应变软化因子n的概念.研究表明,该模型能够合理反映高温作用后多孔砂岩应力应变曲线的变化特征.

Based on the nuclear magnetic resonance and mechanical tests of sandstone after exposure to high temperature,combined with the fractal theory of pore structure,the dual effects of high temperature on the mechanical properties of sandstone were analyzed,and the internal mechanism of pore fractal dimension and mechanical parameters was studied.The results show that the mechanical properties are significantly enhanced in the range of 150~300℃.When the temperature exceeds 450℃,the mechanical properties are weakened.The mesopores and macropores have significant fractal characteristics,and their fractal dimensions are negatively correlated with mechanical parameters,and the nanopores have no fractal characteristics.The segmented constitutive model was established considering the post-peak stress drop.The concept of post-peak strain softening factor n was proposed.The results show that this model can reasonably reflect the variation characteristics of the stress-strain curves of sandstone.