Discrete element simulation of foam concrete under uniaxial compression considering non-spherical pores
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摘要: 为了研究异形孔隙对泡沫混凝土单轴压缩特性的影响,本文对密度等级500 kg/m3的泡沫混凝土开展了 X射线计算机断层扫描(X-CT)试验及单轴压缩-声发射联合试验,基于实测孔结构特征建立了不同非球形颗粒占比的三维细观离散元模型并模拟了单轴压缩过程。结果表明:离散元模型模拟的单轴压缩损伤过程与声发射试验结果基本一致,具有明显的阶段特征;异形颗粒离散元模型能表征初步密实阶段应力-应变曲线的振荡,模拟出应力消散阶段基质的剪切和互锁,在建立泡沫混凝土离散元模型时,应考虑孔隙形状的影响;离散元模型的抗压强度随模型中孔隙非球形率的提高而线性衰减,相关系数达0.94。Abstract: In order to study the fitness of discrete element method (DEM) in the simulation of mechanical properties of foam concrete and the influence of non-spherical pores on the uniaxial compression characteristics of foam concrete, X-ray computed tomography (X-CT) test and uniaxial compression-acoustic emission joint test were carried out on foamed concrete with density of 500 kg/m3. Based on the measured pore structure characteristics, a series of three-dimensional mesoscopic DEM models with different non-spherical particle proportions were established and the uniaxial compression process was simulated. The results show that the uniaxial compression damage process of the model is basically consistent with the acoustic emission test results, which has obvious stage characteristics. The non-spherical particle discrete element model can characterize the oscillation of the stress-strain curve in the initial compaction stage, and simulate the shear and interlocking of the matrix in the stress dissipation stage. When establishing the discrete element model of foam concrete, the influence of pore shape should be considered. The compressive strength of the DEM model decreases linearly with the increase of the non-spherical rate of the pores in the model while the correlation coefficient is 0.94.
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表 1 泡沫混凝土配合比
Table 1. Mix proportion of foam concrete
Sample Mix proportion/(kg·m−3) Wet density/(kg·m−3) Dry density/(kg·m−3) Cement Water Foam agent F500-A 310 186 0.59 523 398 F500-B 310 186 0.59 528 408 F500-C 310 186 0.59 530 415 Notes: The specimen number as F500-A, where F500 represents the wet density level of the specimen, and A represents the specimen number. 表 2 非球形颗粒基本参数
Table 2. Basic parameters of non-spherical particle
Particle Number Coordinate/mm Radius/mm X Y Z A 1 0 2 2 0.5 2 0 0.82 3 0.5 3 0 0.82 2 1 4 0.71 0 2 0.5 5 0 0 0.61 1 6 0 0.82 0 0.5 7 −1.2 −0.3 0.25 0.5 表 3 泡沫混凝土离散元(DEM)模型颗粒统计
Table 3. Particle statistics of discrete element method (DEM) model of foam concrete
Sample Spherical particle volume/mm3 Non-spherical particle volume/mm3 Cement particle volume/mm3 Degree of compaction/% Porosity Deviation from experimental value/% 0%NSP/FCP 399271.10 — 274190.35 67.35 0.593 2.47 20%NSP/FCP 325290.65 86204.16 283082.63 69.46 0.592 2.47 30%NSP/FCP 283944.50 120768.48 285881.79 69.06 0.586 3.62 40%NSP/FCP 248534.41 164424.96 283280.55 69.62 0.593 2.47 Notes: The specimen number as 20%NSP/FCP-1, where 20%NSP/FCP represents the volume ratio of non-spherical pore particles in all pore particles of DEM model of foam concrete, and 1 represents the specimen number. 表 4 泡沫混凝土离散元模型细观参数
Table 4. Mesoscopic parameters of DEM model of foam concrete
Contact parameters of Hertz-Mindlin model Mesoscopic parameters of bonding model Parameter Value Parameter Value Coefficient of restitution 0.2 Normal stiffness per unit area/(N·m−3) 1.55×1010 Coefficient of static friction 0.4 Shear stiffness per unit area/(N·m−3) 1.32×1010 Coefficient of rolling friction 0.04 Critical normal stress/Pa 4.8×106 Poisson's ratio 0.35 Critical shear stress/Pa 4.6×106 -
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