高温后混凝土冲击破碎能耗及分形特征研究

Research on Energy Dissipation and Fractal Characteristics of Concrete after Exposure to Elevated Temperatures under Impact Loading

为研究高温后混凝土在冲击破碎过程中的能量耗散特性及碎块块度分布规律,采用100 mm分离式霍普金森压杆装置,对不同温度(常温、200℃、400℃、600℃、800℃)作用后的混凝土进行冲击压缩实验,分析了冲击弹速和温度对试件冲击破碎能耗、破坏形态及碎块分形维数的影响。研究结果表明:同一温度下,耗散能随弹速和应变率的升高不断增大,同一弹速下,耗散能随温度的升高总体呈下降趋势;冲击破坏后混凝土破碎块度分布是一个统计意义上的分形,随弹速及温度的升高,试件破碎程度增大,碎块数目增多、尺寸减小,分形维数增大;耗散能与碎块分形维数的变化在相同温度下具有一定的正相关性。由此可见,不同温度、弹速下混凝土的冲击破碎是外部能量驱动下的分形演化过程。

The energy dissipation capacities and fragments distribution of concrete exposed to high temperature under impact loading are studied. Dynamic compressive tests of concrete at room temperature and after exposure to elevated temperatures ranging from 200 to 800 ℃ are conducted by using a split Hopkinson pressure bar with 100 mm in diameter. The effects of high temperature and impact velocity on dissipated energy, failure mode and fractal dimension of fragments are analyzed. The results indicate that the dissipated energy grows with the increase in impact velocity and strain rate at the same temperature; and at fixed impact velocity, the dissipated energy decreases with the increase in the exposure temperature. The fragment-size distribution of concrete fragments statistically has fractal property subjected to impact loading. An increase in temperature and impact velocity results in a greater crushing degree and a larger fractal dimension value. There is a positive correlation between dissipated energy and fractal dimension at the same temperature. As a result, the impact crushing of concrete at various temperatures and impact velocities is a fractal evolution process driven by external energy.