水冷却对高温花岗岩的细观损伤及动力学性能影响

为探讨高温花岗岩经水冷却后的细观结构损伤及动态力学性能,对水冷却后高温花岗岩开展波速和核磁共振测试,分离式霍普金森压杆冲击试验,以及冲击破碎试样的扫描电镜观察,分析比较不同状态下花岗岩波速、孔隙度和动力学参数的变化规律。研究发现:随着温度升高,经水冷却处理后高温花岗岩波速非线性下降,大孔径孔隙度分量增大,且水冷却后试样的孔隙孔径尺寸和数量均大于自然冷却;水冷却后高温花岗岩动力学参数呈现出随着温度升高,峰值应力减小,峰值应变增大,弹性模量则先增大后减小的规律;由于水冷却使高温花岗岩表面温度急剧降低,产生额外的温度应力,花岗岩内部损伤加剧,表现出更低的波速与峰值应力;而水的冷淬作用一定程度上提高了表层花岗岩的硬度,降低了高温后花岗岩的塑性能力,与自然冷却相比水冷却后花岗岩的峰值应变减小,弹性模量增大,表现出脆性破坏特征。在温度低于400℃时,冷却方式对冲击裂纹影响不大,随着温度升高到800℃,自然冷却后花岗岩冲击断面呈蜂窝状,而水冷却后冲击断面则相对平整。

Effect of water cooling on microscopic damage and dynamic properties of high-temperature granite

The microscopic damage and dynamic mechanical properties of high-temperature granite after water cooling were studied through wave velocity test, nuclear magnetic resonance (NMR) test, split Hopkinson pressure bar (SHPB) impact test and scanning electron microscope（SEM）test. The variation of porosity and dynamic mechanical parameters of granite were analyzed. The results show that the wave velocity of high-temperature granite decreases nonlinearly after water cooling and the components of porosity with large pore increase with the increase of temperature. Moreover, water cooling leads to the more cracks and greater crack sizes than that of natural cooling. The dynamic parameters of high-temperature granite after water cooling show that the increase in temperature results in a decrease in the peak stress, an increase in the peak strain, and an increase at first then decrease in the elastic modulus. Additional thermal stress, resulted from sharply decrease in surface temperature of the high-temperature granite, leads to increased internal damage and decreased wave velocity and peak stress. Compared with natural cooling, the plasticity of high-temperature granite is reduced, because the cold hardening effect improves the hardness of surface granite. After water cooling, the granite specimens exhibit the brittle failure characteristics and their peak strain decreases but their elastic modulus increases. Cooling way has a minor effect on the cracks induced by shock before 400 ℃. As the temperature up to 800 ℃, the impact fracture surface of granite after natural cooling is characterized by honeycomb and irregular shape, in contrast, the impact fracture surface of granite after the water cooling is relatively flat.