Micromechanics-Based Concrete Model For Realistic Large- Scale Computations of Failure

(1)基于多相复合材料理论，建立了具有不同取向随机微裂纹族的弹性材料切向刚度张量的应变软化本构模型。(2)通过考虑裂纹扩展速率是应力强度因子的函数，将模型推广到矩阵中的速率依赖和粘弹性（蠕变）。(3)将模型进一步扩展到微裂纹前缘的塑性屈服。(4)利用微平面模型的相同优势特征，提出了一种计算算法，并结合材料长度的非局部特征来捕捉断裂行为和尺寸效应。(5)将复合材料理论应用于随机裂纹族扩展，建立了基于软化规律增强的微平面模型的替代模型，并与第一种基本模型进行了比较。(6)通过对单轴、双轴、三轴试验、断裂试验和尺寸效应试验的大量试验数据进行最小二乘法拟合，对模型进行了验证和校准，并在动态有限元程序中实现。该模型还可以很容易地推广到各向同性和各向异性岩石。

The research program consists of six thrusts: (1) Based on the theory of multiphase composite materials, a strain-softening constitutive model for the tangential stiffness tensor of an elastic material with families of random microcracks of different orientations is developed. (2) By considering the crack growth rate to be a function of the stress intensity factor, the model is then generalized to rate dependence and viscoelasticity (creep) in the matrix. (3) The model is further extended for plastic yielding at the fronts of microcracks. (4) A computational algorithm borrowing same advantageous features of the microplane model is formulated, and nonlocal characteristics with a material length are incorporated to capture fracture behavior and size effect. Also (5) an alternative model based on the microplane model enhanced by a softening law based on application of composite material theory to the growth of random crack families is developed and compared to the first outlined basic model, Finally (6) the model is verified and calibrated by least-square fitting of extensive test data from uniaxial, biaxial and triaxial tests, fracture tests and size effect tests, and is implemented in a dynamic finite element program. The model will also allow easy generalization to isotropic and anisotropic rocks.