混凝土梁弯拉断裂过程的细观分析

将混凝土看成是由骨料、砂浆和界面过渡层组成的三相复合材料.结合部分力学参数试验,采用非线性有限元对混凝土梁受弯拉破坏过程进行了数值模拟.按照试件的实际配比,由Walraven公式计算出各种粒径区间骨料的平面等效面积,然后由随机骨料模型生成混凝土数值试件.混凝土细观结构的破坏由最大拉应力准则判别,对于软化段,采用了应力张开位移模型以缓解计算结果的网格依赖性.计算结果表明:界面厚度取0.2～0.8 mm,对试件的荷载位移全曲线的影响不大;任意形状骨料与圆形骨料的计算结果相近;界面层断裂能对梁宏观荷载位移曲线的形状影响较大.

Meso-scopic analysis of fracture process of concrete beam under bending

Concrete is regarded as a three-phase composite consisting of aggregate,mortar matrix and interfacial transition zone.Combining some experiments of mechanical properties for each constituents of concrete,numerical calculations for the concrete beam under bending were performed by nonlinear finite element method.According to the real mixture ratio,the two-dimensional equivalent area for various size distribution range can be calculated by the Walraven formula.Then,numerical concrete specimens are generated by the random aggregate model.The tensile strength failure criterion is used,and stress-displacement model is adopted to alleviate the sensitivity on mesh size in the softening region.Numerical results show that the thickness of the interface between 0.02 and 0.08 mm has little influence on the load-displacement curves,and the results from specimens with circular and random polygonal aggregate are approximately the same, the fracture energy of the interface has remarkable influence on the shape of macro-scopic load-displacement curves.