【作者】 徐辉；

【导师】 卫军； 王靖涛；

【作者基本信息】 华中科技大学 ， 结构工程， 2007， 博士

【摘要】 基于连续损伤力学所建立的损伤模型,只求预计的宏观力学行为符合某种实验结果,而不细察损伤的细观物理与力学过程,因而其适用性受到较大的限制。目前对土的细观损伤研究,仅停留对CT扫描试验中所观测到的现象进行描述和结果的简单归纳上,未能有效地将这些试验现象和成果纳入到土的本构模型中。本文尝试将土的细观损伤机制与唯象损伤理论结合起来,为此,在以下两个方面进行了有益的探索:(1)认为土体骨架在损伤阶段是由完好骨架和破损骨架两相材料组成的复合体,完好骨架的破损遵循Mohr-Coulomb准则,根据应力圆与破损强度包络线的相对位置,计算出破损骨架的体积分数;视完好骨架为复合体中的完善联结夹杂,视破损骨架为复合体中的非完善联结夹杂,运用细观力学中的夹杂理论,给出了求解复合体剪切模量的非线性方程组。与试验结果的对比表明,本文提出的细观力学模型能较好地反映无明显剪胀的土的剪切变形行为。可以适用于复杂应力状态和复杂的应力路径。(2)在工程荷载范围内,忽略骨架颗粒的变形,认为土体骨架的变形是颗粒接触面变形的总和,并且在围压不变的条件下,骨架变形的非线性是源于颗粒接触面之间的滑动。不同的应力水平,会导致不同取向范围内的接触面产生滑动。假定颗粒接触面的滑动遵循Mohr-Coulomb准则,根据应力圆与颗粒滑动包络线的相对位置,计算出该应力状态下滑动接触面的取向范围;并将该取向范围的值与其所能达到的最大值(由骨架整体破坏时的应力圆计算得到)定义为损伤比,然后按照两种接触面的剪切模量进行加权平均得到复合体的剪切模量。复合体的体积变形由两个部分组成,一部分与体积应力相关,另一部分由塑性剪应变引起。选取了排水剪胀砂土和不排水粘土在不同围压,不同固结方式、多种应力路径下的试验数据,验证本文所提出的基于颗粒细观滑动机制的损伤模型。并归纳了损伤比与剪应力、应力比、本文提出的广义应力比之间的关联,结果发现本文提出的损伤比与广义应力比之间有着一一对应的关系,即也可以用广义应力比作为描述损伤状态的参数,颗粒滑动的取向范围的比值与广义应力比只是分别从不同的角度来解释损伤状态,两者给出的结果是一致的。更多还原

【Abstract】 Because the damage constitutive model based on continuum damage mechanics does not concern the physical mechanism of microscopic damage, it seems to only provide an estimate of the macroscopic deformation of soil and its applicability is limited to the particular stress conditions or stress paths. In the present studies for microscopic damage of soil, only the descriptions about the phenomena and the result obtained from the CT test, rather than the constitutive models that can reflect the influence of microscopic damage, are given.This paper explores two methods to establish the microscopic damage constitutive model of soil:(1) Assuming the skeleton of soil is composed of perfect skeleton and damage skeleton in the damage deformation phase, and the conversion from perfect skeleton to damage skeleton obeys Mohr-Coulomb law, a calculation of the volume fraction of damage skeleton is conducted according to the relative distance from the stress circle to the initial damage line. Regarding the perfect skeleton as perfectly bonded impurity and the damage skeleton as imperfectly bonded impurity, the nonlinear functions for calculating the composing modulus are obtained by using micromechanics method. To evaluate the performance of the proposed constitutive model, comparisons between simulated deformation and the actual deformation were conducted. The consequence indicates that the proposed micromechanics model was capable of simulating the nonlinear shear deformation behavior for the soil which has not significant amount of shear dilation.(2) A hypothesis that the skeleton deformation is only the deformation of the interfaces of grains, and the deformation characteristics including nonlinearity, plastic deformation and shear dilation are controlled by the sliding of interfaces of grains within soil skeleton, is presented in this paper. According to the relative distance from the stress circle to the initial sliding envelope line, direction-range value of the sliding interfaces can be determined. The damage ratio is defined as the ratio of the previous direction-range values to its maximum value (determined by failure stress circle). The overall shear modulus is the weighting average of the perfect contact shear modulus and sliding contact shear modulus. The volumetric strain is made up of two parts: the one induced by hydrostatic stress, the other one induced by plastic shear strain. Test on the versatility of the proposed damage model based on the micro-sliding mechanism, including varying hydrostatic stresses, consolidation methods and stress paths, indicate that the proposed micro-sliding damage model is capable of describing deformation characteristics for various conditions. In addition, the relations between damage ration and shear stress, stress ratio and generalized stress ratio proposed in this paper are illustrated and compared. The result reveals that the damage ration has a one-to-one relation with the generalized stress ratio, namely, the generalized stress ratio proposed in this paper can be also used to describe the damage state.更多还原