加载速率及其突变对混凝土压缩破坏影响的数值研究

Effects of loading rate and its sudden change on concrete compressive failure

混凝土动态力学行为具有明显的率相关性,探讨了加载速率及其突变对混凝土压缩破坏模式及宏观力学性能的影响。考虑混凝土细观结构非均质性的影响,从细观角度出发将混凝土看作由骨料、砂浆基质及过渡区界面组成的三相复合材料。采用耦合应变率效应的塑性损伤本构关系模型来描述砂浆基质及界面的动态力学行为;认为骨料不产生断裂破坏,为弹性体。采用Monte Carlo法建立了混凝土二维随机骨料模型,首先对Dilger等混凝土动态压缩试验进行数值模拟,数值与试验结果的良好吻合证明了方法的可行性及细观参数选取的准确性。进而探讨了细观组分应变率效应的影响,对比了混凝土非均质模型与宏观均匀模型的应变率效应,最后分析了软化阶段加载速率突变对混凝土破坏模式及宏观应力-应变关系的影响,并得到了一些有益结论。

The dynamic behavior of concrete has obvious strain-rate dependency.Here,the effects of loading rate and its sudden change on concrete compressive failure pattern and its macroscopic dynamic properties were studied. Considering the influence of concrete heterogeneity,from view point of meso-scale,concrete is treated as a three-phase composite composed of aggregate,mortar matrix and interfacial transition zone （ITZ ） between them.The damaged plasticity theory combined with strain rate effect was used to describe the dynamic properties of mortar matrix and ITZ.It was assumed that aggregate phase does not damage,and thus aggregate is set to be elastic.A planar concrete random aggregate structure was established with Monte Carlo method.The dynamic compressive tests conducted by Dilger et al were simulated at first,and the good agreement between the presented numerical results and the experimental data indicated the feasibility of the presented meso-scopic approach and the reusonableness of the selected meso-scale parameters.Subsequently,the material strain-rate effect was discussed,and the strain-rate effects of a concrete meso-scale heterogeneous model and a concrete macro-scale homogeneous model were compared and studied.Finally,the influence of the sudden change of loading rate during the softening stage on concrete failure mode and macroscopic mechanical properties of concrete was analyzed.Some useful conclusions were obtained.