混凝土断裂过程区及裂缝亚临界扩展的时变演化机理

As the stress corrosion environment exists, evolution of fracture process zone and propagation of subcritical crack will be facilitated due to occurrence, propagation and coalescence of microcracks around the macrocrack tip. The unstable fracturing will happen as a result of long term development and accumulation of this process. Therefore, it could be considered that the delayed fracturing behavior of concrete has a great relation with time-dependent evolution of fracture process zone and propagation of subcritical crack. Based on fracture-damage mechanics and theory of subcritical crack growth, this time-dependent mechanism is deeply studied according to theory analysis, lab tests and numerical simulations in this project. The basic mechanical parameters, crack propagation criterions and the speed parameters of subcritical crack growth for mode I, mode II and I-II mixed cracks in concrete will be obtained through the lab tests. Especially, the detailed time-dependent evolution of fracture process zone is observed during the tests. The corresponding numerical simulations are carried out using the elaborate numerical model which not only considers the random distribution of microcracks and heterogeneity of materials, but also is able to simulate time-dependent variation of both fracture process zone and subcritical crack growth. Then the delayed fracturing behavior of concrete is predicted and the time-dependent evolution mechanism for fracture process zone and subcritical crack growth in concrete is interpreted. This research will provide the new method for the analysis of time-dependent crack propagation and stability for concrete structure.

在一定应力腐蚀条件下，混凝土裂缝尖端的微裂缝会萌生、扩展、贯通和汇合促成断裂过程区的演变及裂缝的亚临界扩展，此过程长期发展累积有可能引发失稳断裂。因而可以认为断裂过程区及裂缝亚临界扩展的时变规律决定了混凝土材料的延迟断裂行为。为此，本项目将基于断裂、损伤力学和亚临界扩展理论，采用理论分析、试验测试与数值计算相结合的方法，对该问题进行深入研究。开展混凝土基本力学试验和I型、II型及I-II复合型裂缝的亚临界扩展试验，获取基本力学参数、裂缝扩展准则和亚临界扩展速度参数，观测断裂过程区的时变规律，建立既能考虑微裂缝随机分布、材料成份各向异性，又能模拟特定荷载下断裂过程区及裂缝亚临界扩展随时间而变的精细化数值模型，预测混凝土的延时断裂行为，揭示混凝土断裂过程区及裂缝亚临界扩展的时变机理。成果有望为裂损混凝土结构裂缝的长期扩展及稳定性分析提供一种新的方法。

本项目基于断裂、损伤力学和亚临界扩展理论，采用理论分析、试验测试与数值计算相结合的方法，对混凝土、砂浆砌体、岩石等脆性材料的亚临界裂纹的时变演化规律及裂缝萌生、扩展、贯通、汇合直至断裂失效的过程进行了研究。首先开展了混凝土抗压、劈裂抗拉、剪切试验与断裂韧度测试，其次进行了各型裂缝的亚临界扩展试验，获取了基本力学参数、裂缝扩展准则和亚临界扩展速度参数，模拟了特定荷载下断裂过程区及裂缝亚临界扩展直至结构失效的全过程，预测混凝土、砂浆砌体、岩石等脆性材料的断裂损伤行为与延时断裂行为。揭示了混凝土等脆性材料断裂过程区及裂缝亚临界扩展的时变机理。成果为上述材料裂损结构的裂纹长期扩展及稳定性分析提供一种新的方法。