混凝土动力破损性能的细观仿真与试验验证

The dynamic strengths and damage-failure properties of concrete behave sensitively to the loading rates when subjected to seismic or impact loads. The phenomenon that dynamic strength of concrete increases with the increasing of strain rate is defined as strain rate effect. Most super-structures, such as high dams are under the risk of encountering earthquakes or impact loadings, so the dynamic behavior of concrete is an important factor related to the seismic safety evaluation. The objective of this study is to explain the mechanism of strain rate effects of concrete including the influence of static pre-loading. Based on the Particle Element Method (PEM), a meso-scale model which considers the heterogeneity of three-phase concrete i.e., aggregate, mortar, and interface will be employed to study the dynamic failure behavior of concrete. The meso-mechanical parameters of three phases of concrete are determined by inverse method and the complete force-deformation relationships and damage-failure processes at different strain rates can be obtained by simulating dynamic flexure tests of concrete beams. The transitions between strain energy, kinetic energy and frictional energy consumption will be discussed to explain the mechanism of strain rate effects of concrete. Furthermore, the influence of static pre-loading on the dynamic strength of concrete will also be investigated in the study. Based on the dynamic splitting tests by Split Hopkinson Pressure Bar (SHPB) for concrete strengths at high strain rates, dynamic flexure tests by Drop Hammer tests are planned to study the dynamic constitutive relationships of concrete at medium-high strain rates. The meso-scale PEM model will be improved and verified according to the results of experiments, by overall contrast, including the different fracture processes and failure modes at different strain rates. Further explanations of the mechanism of the dynamic properties of concrete will be proposed.

混凝土在地震动与高速冲击荷载作用下其强度本构关系与破坏性能显示出明显的与加载速率密切相关的特征。随加载速率的提高，其强度表现出显著增长的率效应，这一现象对高坝等大型结构的动力安全稳定性评价具有重大影响。本项研究目标是探索混凝土动力率相关效应和不同荷载环境及初载历史的影响机理。 基于混凝土细观颗粒元仿真模型，考虑骨料、砂浆、交界面三相的强度非均匀性，考虑初始静力加载等初载条件，以不同加载速率施加荷载，考察混凝土材料的动力损伤断裂破坏全过程，并分析应变能-动能-摩阻耗能的全程变化，从而揭示混凝土动力率相关效应的内在机理。 在试验验证方面，在霍普金森杆冲击劈拉试验基础上，采用中-高速率的重力落锤试验装置，进行混凝土动力弯曲试验，研究其动力本构关系与应变率的关系，观察不同速率的损伤断裂过程与破坏形态。据此与细观数值仿真成果进行全面对比，从而进一步解释率相关效应的机理，并验证与改进细观模型。

本项研究基于混凝土细观颗粒元仿真模型，考虑骨料、砂浆、交界面三相的强度非均匀性，考察混凝土材料的动力损伤断裂破坏全过程，并分析应变能-动能-摩阻耗能的全程变化。基于细观颗粒元建立落锤-结构全系统仿真模型，对冲击试验进行全过程模拟，研究了系统能量的转化过程，并提出颗粒元能量模式与传统断裂能的转换关系。基于颗粒元-有限差耦合方法，建立无粘结预应力混凝土梁冲击试验仿真模型，其中混凝土颗粒单元和钢筋杆单元在锚固点交互作用，对混凝土损伤断裂和钢筋屈服的动力破坏过程进行模拟，并与试验结果进行了比较研究。细观数值仿真成果与混凝土动力试验进行全面对比，从而进一步解释率相关效应的机理，并验证与改进细观模型。.在试验验证方面，建立稳定可靠的混凝土落锤冲击试验测试系统，通过改变重锤质量、下落高度和锤头材料完成了不同加载速率的冲击试验，对试验中混凝土梁的承载力、动态位移、应变、断裂过程、动量-冲量平衡关系、惯性力和断裂能等动力特性进行了测量和分析。设计了无粘结预应力混凝土梁冲击试验，对钢筋屈服-混凝土断裂的非线性相互作用过程进行系统分析，证明预应力钢筋限制了混凝土的变形和裂纹扩展，钢筋的屈服程度决定了混凝土的裂纹扩展程度和多次冲击的剩余承载力。