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

（1）基于多相复合材料理论，建立了含不同取向随机微裂纹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，然后将该模型推广到速率依赖性和粘弹性（蠕变）的矩阵。 (3)该模型被进一步扩展为塑性屈服在微裂纹的前沿。 (4)一个计算算法借用相同的微平面模型的优点制定，并与材料长度的非局部特性纳入捕捉断裂行为和尺寸效应。 （5）提出了一种基于微平面模型的可供选择的模型，并与第一种基本模型进行了比较。（6）通过单轴、双轴和三轴试验、断裂试验和尺寸效应试验的大量试验数据的最小二乘拟合，对该模型进行了验证和标定。并在动态有限元程序中实现。 该模型也将允许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.