摘要
本文从细观层次出发,将混凝土视为由水泥砂浆,粗骨料及两者间的粘结带所组成的复合材料。利用蒙特卡罗方法生成混凝土随机骨料模型。在此基础上,采用双折线损伤演化模型描述混凝土细观各相单元的损伤退化。利用非线性有限元方法对湿筛及全级配混凝土试件的宏观力学性能进行了数值分析。本文研究工作的主要内容有:
1.根据已有的实验资料,对二级配、三级配、四级配混凝土立方体试件进行了压缩试验,抗压强度所表现的尺寸效应与实验结果基本吻合。裂纹起始于粘结面上并沿平行于最大压应力的方向扩展。
2.在随机骨料模型的基础上,建立了连续粒径的随机骨料模型。在二级配混凝土试件的单轴拉伸试验中验证了均匀化方法,并应用该法对四级配混凝土试件进行了轴拉试验。
3.采用以位移控制的有限元加载程序对二级配、三级配、四级配混凝土梁四点弯试验进行了数值分析,得到了对应的应力-应变全曲线。并对它们的抗弯强度进行了尺寸效应和级配效应分析。
4.按照《水工建筑物抗震设计规范》提出动态本构模型。对二级配混凝土立方体试件和四级配混凝土立方体试件在冲击荷载作用下的细观破坏机制进行数值模拟,给出了试件的应力-应变曲线和动态抗压强度。
5.根据混凝土及组分材料关于应变率效应的实验成果,建立了考虑应变率强化效应的动态损伤本构模型。对全级配混凝土梁在冲击荷载和三角形循环荷载、预静载作用下的破坏机制进行了数值模拟,数值模拟所得结果与实验结果具有较好的一致性。
6.基于均匀化的思想,建立了三维随机骨料模型,结合ANSYS软件的网格剖分,二次开发AUTOCAD,编制VB程序实现了骨料及各相细观单元的可视化。
7.将双折线损伤模型推广到三维,采用该模型对一级配混凝土圆柱体试件、二级配混凝土圆柱体试件和立方体试件、三级配混凝土立方体试件进行了单轴压缩试验。
The concrete is considered as a three-phase composite composed of matrix, aggregate and interface between them on meso-level in this dissertation. Its mesoscale structure is represented with random aggregate model by using Monte-Carlo method. Then, the bilinear damage evolution model is adopted to describe the meso-element’s damage devolution. The macro-mechanical properties of wet-screened concrete and fully-graded concrete are simulated with non-liner FEM, The major research work is summarized as follows:
1. According to the test data, the axial compression tests of two-graded, three-graded, four-graded concrete cubic specimens were simulated. Size effect on the compression strengths got from numerical simulation is fitted with the experiment results. Cracks are generated from the interface and extended in a direction parallel to the maximum compression stress.
2. Based on the random aggregate model, the continuous grain size’s aggregate model is established. Homogenization is verified in the axial tension tests of two-graded concrete and applied in the axial tension test of four-graded concrete.
3. The bending-tension tests of two-graded, three-graded, four-graded concrete beam were simulated using displacement-controlled FEM. The corresponding total stress-strain curves were got. Furthermore, size effect and grade effect on the bending strengths are analysised.
4. According to the Specifications of Seismic Design of Hydraulic Structures, the dynamic damage model of meso-element is developed. Based on this model, the microscopic failure mechanism of two-graded, four-graded concrete under impact loading is simulated. The dynamic stress-strain curve of specimens and their dynamic compression strengths were got.
5. Based on the existed experimental data on the concrete and composited material’s strain-rate effect, the dynamic damage constitive model considering strain-rate strengthening effect is developed. The failure mechanism of fully-graded concrete beam under impact loading, triangle wave load, dynamic load coupling with initial static loading were simulated. The results obtained from numerical simulation have a good fit with experimental data.
6. 3D random aggregate model was proposed based on the homogeneation. Furthermore, combining the mesh generation of ANSYS, this paper brought forward a method of using secondary development in AutoCAD by VB programming to realize 3D visualization of aggregates and meso-elements.
7. The bilinear damage evolution model is extended to 3D. The compression tests of one-graded cylinder concrete specimen, two-graded cylinder concrete specimen and cubic concrete specimen, three-graded cubic concrete specimen is simulated.
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