混凝土高温动态劈拉行为细观数值分析

为研究高温作用下混凝土的动态劈裂拉伸破坏行为，考虑了力学性能的高温退化与应变率增强效应的联合作用，结合混凝土材料内部非均质性，建立了细观尺度数值分析模型与方法。将该数值方法分为两个步骤:首先对混凝土进行热传导行为模拟，进而将输出结果作为初始条件对混凝土动态劈裂拉伸行为进行细观模拟。在模拟结果与已有试验现象良好吻合的基础上，分析了高温下混凝土动态劈裂拉伸行为及其细观破坏机制，对比了不同应变率及加热温度下混凝土的劈裂拉伸应力-应变关系，揭示了混凝土应变率效应与温度退化效应的相互影响规律。研究结果表明:(1) 高温作用后，试件损伤区域较常温下更集中；(2) 名义应变率较大时，破坏过程急促，常温下骨料发生破坏，而经历高温后骨料基本没有破坏；(3) 由于混凝土试件细观结构的非均质性，其内部应力呈枣核状不连续分布；(4) 相比于应变率效应，混凝土劈裂拉伸强度受温度退化作用的影响更显著。

Meso-scale simulations on dynamic splitting tensile behaviors of concrete at elevated temperatures

To study the dynamic splitting tensile fracture behaviors of concrete at elevated temperatures, the numerical meso-scale model and method are established by considering the coupling effects of the high temperature degradation and strain rate enhancement of the mechanical properties, and combining with the internal heterogeneities of concrete materials. The simulation method is divided into two steps: the heat conduction behavior is first simulated, then the output results areused as the initial conditions to simulate the dynamic splitting tensile behaviors of the concrete. Based on the good agreement between the numerical simulation results and the experimental phenomenon, the dynamic splitting tensile behaviors and meso-scale failure mechanism of the concrete at elevated temperature are analyzed, the splitting tensile stress-strain relations of the concrete at different strain rates and high temperatures are compared, and the interacting regulation between the temperature degradation and the strain rate effect of concrete is revealed. The results prove that: (1) after high temperature, the damage area in the concrete is more concentrated; (2) the destructed process becomes more rapid as the nominal strain rate is higher, the aggregation is destroyed at room temperature; (3) the internal stress appears date-shaped distributions due to the heterogeneities of the concrete microstructures; (4) the temperature degradation effects on the splitting tensile strength of the concrete is more dramatic comparing with the strain rate effects.