基于基面力元法的再生混凝土细观损伤研究

摘要

根据再生混凝土的细观结构特点,建立三维球形随机骨料模型;基于M-H细观结构模型,识别再生粗骨料单元、老砂浆单元、新砂浆单元、老黏结带单元、新黏结带单元,并赋予相应的力学参数.基于连续介质学理论及"基面力元法",推导空间八节点正六面体单元刚度矩阵及单元应变显式表达式,建立三维基面力元数值模型.运用自编的再生混凝土损伤问题的三维基面力元程序,通过位移加载,模拟再生混凝土的单轴压缩试验.结果表明:三维球形随机骨料模型能够较好反应再生混凝土的细观结构特征;荷载作用下,内部微裂纹首先出现在老黏结带及新黏结带,最终绕过骨料贯通;基于"基面力元法"的单元刚度矩阵及单元应变具有精确的表达式,计算速度快且能够有效避免数值积分带来的精度损失,可以用于研究非均质材料的断裂机理及细观损伤分析.%According to the mesoscopic structure of recycled concrete,a three-dimensional spherical random aggregate model was es-tablished.Based on the M-H mesostructure model,the natural coarse aggregate elements,old mortar elements,new mortar elements,old in-terfacial transition zone (old ITZ)elements and new interfacial transition zone (new ITZ)elements on mesolevel was identified and the cor-responding mechanical parameters was given.Based on the theory of continuous medium and base force element method (BFEM),the ex-plicit expression of the regular hexahedron element stiffness matrix and the element strain are deduced,and the three-dimensional base force numerical model was developed.Using the three-dimensional base force element damage program(3-D BFED),the uniaxial compres-sion test of recycled concrete was simulated by displacement loading.The results shows that the three-dimensional spherical random aggre-gate model can be agreed with the mesostructure characteristics of recycled concrete.The internal microcracks first appeared in the old ITZ and then the new ITZ,and finally through the aggregate under the load.Based on the BFEM,the element stiffness matrix and the element strain has a precise expression which can rapidly and effectively avoid the precision loss caused by numerical integration,and BFEM can be used to investigate fracture mechanism and simulate mechanical properties for heterogeneous materials.