热-力耦合作用下纤维混凝土力学性能演化规律及其微观机理的研究

With the development of subways, tunnels, high-rise and super high-rise buildings, people start to pay more attention to those damages on concrete materials specifically caused by fire. When the fire breaks out, the concrete undergoes the effecting both by high temperature and structural load. Therefore, researches of the concrete performance change rule and the deterioration mechanism considering the action of thermo-mechanical coupling, is of important theoretical and application value. Taking fiber reinforced concrete as investigating objects, this project will try to explore the variety law of mechanical properties of materials under the coupled action of heat and load by means of the experimental method of applying heating and loading simultaneously. According to the real-time loading system of environmental electron microscopy, the stress-strain variety law and real-time microscopic characteristics of materials at different temperatures will be analyzed to clarify the microscopic mechanism of degradation of material properties. The relationship between the microstructure evolution of materials and the macroscopic mechanical properties degradation will be revealed. The damage evolution process of the materials under the effect of thermo-mechanical coupling will be monitored. Based on the micro-damage mechanics, the internal-damage nucleation regulation of materials under the interaction of high temperature and structural load is investigated to reveal the initiation nature of damage and establish the coupled equations of thermo-mechanical damage. The complementary energy release rates of coupled thermal-mechanical elastic and viscoelastic damages are explored and the failure energy criterion of coupled thermal-mechanical damage is structured. The achievements will provide theoretical basis for safety evaluation of material and structure of major projects encountering the fire.

随着地铁、隧道、高层超高层等建筑物及构筑物的发展，火灾对混凝土结构材料的损伤越发引起人们关注。由于火灾发生时，混凝土是处于高温与结构荷载共同作用下，因此，研究热-力耦合作用下（高温中），混凝土性能变化规律及其劣化机理具有重要的理论及应用价值。本项目以纤维混凝土为研究对象，拟采用加温加载同时进行的实验方法，探索在热-力耦合作用下，材料力学性能的变化规律；采用环境扫描电子显微镜实时加载系统，对材料在不同温度作用下应力-应变变化规律及实时微观特征进行分析，阐明材料微结构演化与宏观力学性能劣化之间的关系；监测材料在热-力耦合作用下损伤演化过程，从微观损伤力学的角度，研究材料内损伤成核规律，揭示材料损伤萌生的本质，建立材料热-力耦合损伤方程；探求材料热-力耦合弹性及粘弹性损伤余能释放率，建立材料热-力耦合损伤破坏的能量准则。成果将为判断重大工程遭遇火灾时材料及结构安全性提供理论依据。

研究了热-力耦合作用下纤维混凝土力学性能演化规律及其微观机理，探寻了混凝土热-力耦合损伤测试及表征问题的解决方法。采用预持荷载与非预持荷载两种试验方案，利用声发射全程监测设备，对混凝土损伤过程中的声发射响应进行实时监控，分析了热-力耦合作用下混凝土力学性能变化与声发射响应二者之间的关系，建立了声发射参数变化规律与宏观试验结论之间的联系。随着温度的上升，混凝土在热-力耦合作用下抗压强度呈现先升高再降低的趋势；200℃、400℃为热-力耦合作用下混凝土抗压强度变化的转折温度；纤维的掺入能有效缓解高温中混凝土抗压强度的衰减。对比了各类混凝土在热-力耦合作用下抗压性能的劣化规律，阐明了纤维的掺入可以提高热-力耦合作用下混凝土抗高温的能力，为纤维的掺入改善高温中混凝土性能提供理论支撑。.采用环境扫描电子显微镜加载系统，对混凝土在不同温度作用下应力-应变曲线变化规律及微观特征进行分析，阐明混凝土微结构演化与宏观力学性能劣化之间的关系；利用声发射振铃计数率表征混凝土热-力耦合作用下的实时损伤，探寻温度与荷载交互作用时材料内部损伤演化规律，从微观损伤力学的角度，研究了材料内损伤及材料损伤萌生的本质，探寻了混凝土损伤破坏的能量准则，建立了热-力耦合作用下混凝土损伤方程及本构关系。200℃条件下PVA纤维和PP纤维依然可以延缓抗拉试件的断裂；400℃条件下混凝土抗拉强度得到了进一步的提高等重要结论。通过宏观、微观试验的系统研究，解决了热-力耦合作用下混凝土性能劣化的测试及表征问题，阐明了混凝土在高温下抗拉性能的退化规律，分析了在高温条件下纤维的掺入对混凝土损伤抑制的机理，为研究火灾及高温环境下纤维混凝土材料性能退化及结构安全性提供科学依据。