双轴受压状态下的高延性纤维增强水泥基复合材料本构模型

基于Darwin和Pecknold考虑混凝土双轴力学行为的方法，建立一个同时考虑双轴受压状态下非线性力学行为和抗压强度变化的高延性纤维增强水泥基复合材料(ECC)二维正交各向异性本构模型。在因双轴加载而产生的正交各向异性的2个方向上引入等效单轴应变，建立非线性应力-等效单轴应变关系以考虑ECC的双轴非线性行为，并采用一条双轴强度包络线确定2个方向上的抗压强度。推导模型的显式数值算法，编写包含该算法的用户自定义材料子程序UMAT，并嵌于有限元计算程序ABAQUS v6.14中。通过对两组不同配合比的ECC试件在不同应力比下的双轴受压加载试验进行数值分析验证本模型的有效性。数值计算得到的主压应力方向上的应力-应变曲线及预测的抗压强度与试验结果吻合较好，表明该文提出的本构模型能够有效地预测ECC在双轴受压状态下的非线性力学行为和破坏强度。

CONSTITUTIVE MODEL FOR ENGINEERED CEMENTITIOUS COMPOSITES UNDER BIAXIAL COMPRESSION

Based on the Darwin-Pecknold method considering the biaxial behavior of concrete, a two-dimensional constitutive model for engineered cementitious composites (ECC) is developed, taking into account the nonlinear mechanical behavior and the variation of compressive strength under biaxial compression. A nonlinear stress-equivalent uniaxial strain relationship is established after introducing the equivalent uniaxial strain in two orthotropic directions caused by biaxial loading to account for the biaxial nonlinear behavior of ECC. A biaxial strength envelope is used to determine the compressive strengths of the two directions. An explicit numerical algorithm of the model is derived, and user-defined material subroutine UMAT containing the numerical algorithm is coded and implemented in finite element procedure ABAQUS v6.14. The efficiency of the proposed model is validated through numerical simulations of two sets of ECC specimens with different mix proportions under biaxial compression loading at various biaxial stress ratios. The stress-strain curves and the compressive strengths in the major compressive stress direction obtained by numerical simulations are in a good agreement with the experimental results. It is shown that the proposed constitutive model can effectively predict the biaxial nonlinear mechanical behavior and the failure strengths of ECC under biaxial compression.