应变率突增对混凝土动态拉伸破坏影响的细观模拟

实际工程中混凝土结构往往遭遇多次动态荷载作用或在承受一定初始损伤荷载基础上再承受不同应变率的动态荷载。建立了哑铃型混凝土三维细观数值模型,模拟不同名义应变率单独作用下混凝土材料的单轴动态拉伸破坏行为,又分别对混凝土单轴拉伸应力应变曲线上升段和软化段的应变率突增行为开展了细观模拟,初步分析了应变率突增行为对动态拉伸破坏强度特性及宏观应力应变曲线的影响。研究结果表明:在低应变率下混凝土拉伸应变率硬化效应相对较弱,而在高应变率下应变率硬化效应显著增强;在加载上升段应变率突增后加载获得的动态拉伸强度和峰值应变均得到了明显提高;在软化段应变率突增时,混凝土试件的“软化行为”转变为“硬化行为”,宏观应力-应变曲线会出现二次峰值;以初始应变率与突变应变率组合加载得到的动态拉伸强度均低于以突变应变率单独加载得到的拉伸强度,并且强度下降的百分比均随着应变率的增大而增大。

Effect of the sudden increase of strain rate on concrete dynamic tensile failure based on 3D meso-scale simulation

In civil engineering,concrete structures often suffer from multiple dynamic loadings,or being subject to dynamic loadings with different strain rates on the base of initial loadings.In the study,a three-dimensional meso-scale numerical model of dumbbell-shaped concrete was established.The uniaxial dynamic tensile failure behavior of concrete materials under different nominal strain rates was simulated.The sudden increase of strain rate in the hardening and softening stages of a concrete uniaxial tensile stress-strain curve were also simulated in meso-scale.The effects of the sudden increase of strain rate on the dynamic tensile failure behavior and stress-strain curves were analyzed.The results show that the strain rate effect of concrete is relatively weak under low strain rate,while the strain rate effect is significantly enhanced under high strain rate.The dynamic tensile strength and corresponding peak strain resulted in by loading after the sudden increase of strain rate in the hardening stage are significantly enhanced.When the sudden increase of strain rate happens in the softening stage,the“softening behavior”changes to the“hardening behavior”,and a secondary peak appears on the stress-strain curve.The dynamic tensile strength obtained under combined loadings of initial strain rate and sudden strain rate is lower than that obtained under single loading of sudden strain rate,and the percentage of the decrease in strength increases with the increasing strain rate.