混凝土试样单轴压缩端面效应及破坏数值模拟

采用复合型界面损伤本构模型,数值模拟了不同端面约束条件下混凝土立方体试样的单轴压缩试验,分析了端面约束对试样变形特征和破坏过程的影响.考虑两种理想端面约束条件,以试样上、下端面垂直于加载方向的侧向变形完全不受试验机加载端头限制模拟光滑端面条件,以试样上、下端面侧向变形完全被限制模拟粗糙端面条件.数值结果表明,端面粗糙条件下得到的试样峰值应力高于光滑端面,对应的峰值应变也是如此;相比于光滑端面,端面粗糙条件下试样的应力-应变曲线所围面积较大,而且曲线峰后软化段表现出更好的延性;光滑端面条件下试样破坏的宏观表现形式为轴向劈裂,粗糙端面条件下则是以在试样上、下端部形成正倒相连的锥形为特征的破坏形式.数值模拟结果可在众多的试验结果中找到佐证.

Numerical simulation for failure process and effect of boundary restraint of concrete specimens in uniaxial compression

The deformation and fracture behavior of concrete specimens under different boundary conditions subjected to uniaxial compressive loading is simulated using the mixed interface damage constitutive model. In order to investigate the effect of the boundary restraints on the test results, two different simplified boundary conditions are applied both at the specimen top and bottom surfaces. The nodes at which boundary conditions are composed are considered as constrained in the lateral direction orthogonal to the applied load. This boundary condition is referred to as rough boundary. On the contrary, it is referred to smooth boundary when the same nodes are considered as free in the lateral direction. The peak stress of the test carried out with rough boundary is higher than that of smooth boundary. The same trend is also found for the strains at peak stress. For the smooth boundary test the post-peak slope of the stress-strain curve is steeper coinciding with a lower ductility. In the case of rough boundary test it has a higher tail of the softening curve and the area below the stress-strain curve is larger. When the smooth boundary condition is used, the failure occurs through a longitudinal splitting crack. Otherwise, specimen spalls at the mid-height of the specimen and the well-known pyramids arise at the specimen ends. The agreement between the numerical and experimental results is satisfactory.