基于细观力学的混凝土弹塑脆性损伤研究

Studies on the microscopic elastic-plastic brittle damage of concrete

将混凝土假定为一种由硬化水泥砂浆、粗骨料、界面粘结带所组成的三相复合材料,在满足骨料级配曲线算法的基础上,采用细观单元的弹塑脆性损伤本构关系,考虑材料的非均质特性,建立了基于细观力学的混凝土弹塑脆性损伤数值模型;分别研究了单轴受拉预置裂纹试样和单轴受压混凝土试样的细观弹塑脆性损伤破坏行为,并揭示了混凝土的宏观表征强度存在明显的尺寸效应,通过将计算结果与Bazant尺寸效应公式、单轴受压物理实验曲线进行对比,验证了模型的正确性。数值试验表明:该模型可以清晰地模拟混凝土细观塑性屈服和失效裂纹的萌生和扩展。骨料与水泥砂浆间的界面粘结带相对薄弱,在混凝土试件形成宏观损伤局部化带前,试件的屈服和破坏首先发生在骨料边缘处的界面位置,并沿着界面粘结带扩展、贯通;同时,导致宏观裂纹形成和发展的因素仍以细观单元的拉伸破坏为主。

It is assumed that concrete is a three-phase composite material consists of hardened cement mortar,coarse aggregate and interfacial adhesive tape.Based on the aggregate gradation curve algorithm,by using elastic-plastic brittle mesoscopic elements damage structure and by considering the heterogeneity of the material properties,an elastic-plastic brittle damage numerical model of concrete based on micromechanics is established.The uniaxial tension and uniaxial compressive pre-cracked specimens for microscopic specimens of concrete elastic-plastic brittle damage destruction are investigated,and the strength of concrete characterization obvious macroscopic size effect is revealed.Through the comparison of results of Bazant size effect formula and the uniaxial compressive experimental curves,the correctiveness of the model is verified.Numerical results show that,the model can clearly simulate mesoscopic plastic yielding and failure of crack initiation and propagation.The aggregate and cement mortar interface between the adhesive tape is relatively weak,before the formation of macroscopic concrete specimens with front damage localization,specimen yield and failure first occurs at the interface position at the edge of the aggregate and expand along with the interface.Simultaneously,the reason of the formation and development of macro-cracks are still mainly dependent upon the tensile failure of meso-unit.