加载速率对混凝土拉伸破坏行为影响观数值分析

探讨了加载速率及细观结构非均质性对混凝土破坏模式及宏观力学性能的影响。考虑到混凝土细观结构非均质性的影响,将混凝土看作由骨料和砂浆基质组成的两相复合材料。考虑材料的应变率效应,采用塑性损伤模型来描述砂浆基质的动态力学行为;由于骨料具有较高强度,假定不会产生断裂,设定为弹性体。对单边缺口的混凝土试件及L形试件在不同加载速率下的动态拉伸破坏模式进行了细观数值研究。数值结果表明:1) 混凝土动态破坏模式及裂纹扩展方向具有明显的加载速率相关性;2) 随着加载速率的提高,混凝土破坏模式从I-型模式到混合型模式转变;3) 混凝土细观结构越复杂,组分间相互作用越复杂,裂纹扩展路径越复杂,裂纹分支现象越为明显;4) 随着加载速率的提高,混凝土破坏时产生更多的裂纹扩展路径(分支裂纹),且损伤区域宽度增大,导致混凝土在高应变率作用下消耗更多的能量,可认为是混凝土材料动态强度提高的主要原因。

MESO-SCALE NUMERICAL ANALYSIS OF THE EFFECT OF LOADING RATE ON THETENSILE FAILURE BEHAVIOR OF CONCRETE

The effects of loading rate and heterogeneity of meso-structure on the failure pattern and the macroscopic dynamic mechanical properties of concrete are investigated. Considering the effect of concrete heterogeneity, concrete is simulated as a two-phase composite composed of aggregate and mortar matrix at meso-scale in this work. The strain-rate effect is also accounted for and the damaged plasticity theory is employed to describe the mechanical behavior of mortar matrix. It is assumed that the aggregate phase cannot be damaged due to high strength, and thus the aggregate particles are set to be elastic. The dynamic tensile failure modes of a single-edge notched concrete specimen and an L-shaped specimen are numerically simulated. The simulation results indicate that the dynamic failure pattern and the direction of crack propagation of concrete have pronounced loading rate dependency. With the increase of loading rate, the failure mode of concrete changes from mode-I to mixed mode. A more complex meso-structure leads to a stronger interaction between the components and more complicated crack paths, and a more obvious crack branching behavior. Furthermore, as loading rate increases much more branching cracks occur within concrete and the width of the damaged region increases, implying that the fracture process at high strain rates requires more energy demand to reach failure. This should be the main reason for an increased dynamic strength of concrete.