中文摘要：

该文以各组分体积不变为准则建立了考虑温度影响的混凝土三相微观断裂球体模型。将混凝土组成简化为骨料,水及水泥浆体,并以模型中各层模拟;认为高温下混凝土的断裂为模型中间层水汽蒸发逸出的结果。通过气体状态方程分析了模型内部气压随温度的变化,并研究了骨料和水泥浆体层的应力状态。分析了含圆盘形裂纹的混凝土的可释放弹性能和表面能,并根据Griffith断裂准则给出了混凝土断裂韧性随温度的变化规律。对该文模型进行数值模拟,并与相关试验结果对比,结果证明了该文模型能够有效地计算高温下和高温后混凝土的断裂韧性。同时分析发现：随着温度的升高,混凝土可释放弹性能增大而开裂时的裂纹初始长度将减小。

英文摘要：

A three-phase micro fracture spherical model for concrete considering the influence of temperature is established based on a rule that volumes of each component in the model are the same as those of the real material. The components of concrete is simplified as aggregate, water and cement paste, and each part is modeled as a spherical layer. Cracking of concrete at elevated temperature is considered to be the result of evaporation and escape of the water in the mid-layer. The gas state equation is employed to determine the internal pressure of the model, and the stress states of the aggregate and cement paste layers are studied as well. The releasable elastic energy and the surface energy are investigated for concrete which has a penny-shaped crack. According to the Griffith fracture criterion, the relation between fracture toughness for concrete and temperature is clarified. Numerical calculations are conducted for this present model, and a comparison with the test data is performed. Results indicate the validation of the model in calculating the fracture toughness of concrete at and after elevated temperature. This study addresses a fact that： as the temperature increases, the fracture toughness increases while the initial length of crack where the fracture takes place for concrete decreases.