Li Yan, Zhai Yue, Liu Xuyang, Liang Wenbiao
School of Geology Engineering and Geomatics, Chang'an University, Xi'an 710054, China.
School of Civil Engineering, Chang'an University, Xi'an 710061, China.
Materials (Basel). 2019 Aug 14;12(16):2585. doi: 10.3390/ma12162585.
In order to study the fractal characteristics and energy dissipation of concrete suffered freeze-thaw cycle actions and impact loading, C35 concrete was taken as the research object in this paper, and freeze-thaw cycle tests were carried out with a freeze-thaw range of -20 °C20 °C and a freeze-thaw frequency of 050 times. The degradation characteristics of concrete material and the variation rules of basic physical parameters under various freeze-thaw cycle conditions were obtained consequently. By using the SHPB (separated Hopkinson pressure bar) test device, impact compression tests of concrete specimens under different freeze-thaw cycle actions were developed, then the process of impact crushing and the mechanism of damage evolution were analyzed. Based on the screening statistical method and the fractal theory, the scale-mass distribution rules and fractal dimension characteristics of crushing blocks are investigated. Furthermore, the absorption energy, fracture energy and block kinetic energy of concrete under different conditions were calculated according to the energy dissipation principle of SHPB test. The relationship between the energy consumption density and the fractal dimension of fragments was established, and the coupling effect mechanism of freeze-thaw cycle action and strain rate effect on the fractal characteristics and energy consumption was revealed additionally. The research results show that the concrete under different freeze-thaw cycle conditions and impact loading speeds has fractal properties from the microscopic damage to the macroscopic fracture. The energy dissipation is intrinsically related to the fractal characteristics, and the energy consumption density increases with the increase of the fractal dimension under a certain freeze-thaw cycle condition. When at a certain loading speed, with the growth of freeze-thaw cycles, the energy consumption density reduces under the same fractal dimension, while the fractal dimension improves under the same energy consumption density.
为研究经历冻融循环作用和冲击荷载的混凝土的分形特征及能量耗散，本文以C35混凝土为研究对象，开展了冻融范围为-20℃20℃、冻融次数为050次的冻融循环试验，从而得到了不同冻融循环条件下混凝土材料的劣化特征及基本物理参数的变化规律。利用SHPB（分离式霍普金森压杆）试验装置，开展了不同冻融循环作用下混凝土试件的冲击压缩试验，进而分析了冲击破碎过程及损伤演化机理。基于筛分统计方法和分形理论，研究了破碎块体的粒度-质量分布规律及分形维数特征。此外，根据SHPB试验的能量耗散原理，计算了不同条件下混凝土的吸收能量、断裂能量及块体动能。建立了能量消耗密度与碎片分形维数之间的关系，揭示了冻融循环作用与应变率效应在分形特征和能量消耗方面的耦合作用机理。研究结果表明，不同冻融循环条件及冲击加载速度下的混凝土，从细观损伤到宏观断裂均具有分形特性。能量耗散与分形特征存在内在联系，在一定冻融循环条件下，能量消耗密度随分形维数的增大而增大。当加载速度一定时，随着冻融循环次数的增加，在相同分形维数下能量消耗密度降低，而在相同能量消耗密度下分形维数提高。
