基于随机损伤模型的混凝土轴拉破坏过程研究

 采用一维细观力学随机损伤模型，从材料加载过程中损伤能量耗散与应变能释放之间的能量平衡出发，对混凝土试件单轴拉伸破坏过程的稳定性进行分析并得到了破坏过程稳定开展的判定条件。利用这一条件确定了材料由均匀损伤过渡到局部损伤的临界状态，同时指出临界状态异于且滞后于峰值应力状态。临界状态后若为非稳定破坏将发生应力跌落，是材料脆性破坏的表现，若为稳定破坏则材料延性更为明显。理论分析结果表明，包含应力跌落的应力–应变软化不仅与材料力学性能的非均匀性有关，还与试件结构尺寸有关，具有明显的尺寸效应，不能视为单纯的材料属性。最后分别以材料极限应变服从Weibull分布和对数正态分布描述材料的非均匀性，对不同尺寸的混凝土试件轴拉破坏过程进行模拟，表明了所给出结论的合理性。

RESEARCH ON CONCRETE FAILURE PROCESS UNDER UNIAXIAL TENSION BASED ON STOCHASTIC DAMAGE MODEL

A one-dimensional stochastic mesomechanical damage model is adopted to study the failure process of concrete specimen subjected to uniaxial tension. A balance is taken into account between the dissipated energy in damage evolution and the released elastic strain energy of the specimen during the loading process. The stability analysis of the failure process is conducted；and a stability criterion of the failure process for uniaxial tension test of concrete is derived based on energy principle. The critical state is defined according to the criterion，which is a transition from uniform damage to local damage；and the state is different from the peak stress state and lags behind it. The instable failure process of concrete specimen is accompanied by stress significantly decreased and it indicates that the specimen will fail in a brittle manner，while the stable failure process shows more ductility. Theoretical analysis indicates that the stress-strain curve shape，which includes a sudden decline in stress，is not only affected by the material heterogeneity but also by the length of the test specimens. To describe the heterogeneity，it is regarded that the material failure strain is given by a homogeneous，lognormal or Weibull random distribution. Finally，the failure processes of several concrete specimens under uniaxial tension are simulated with different lengths.