砂土的物态本构模型

基于砂土的压缩回胀性、剪切非线性及剪缩剪胀性的系统分析和包括循环荷载、主应力轴旋转及应力路径偏转等复杂应力条件下的复杂变形反应,得到了三类应力-应变基本关系。在剪缩剪胀应力-应变关系中,引入了由偏应变分量确定的应变路径长度变量,揭示了应力主轴旋转、应力路径偏转引起的剪缩剪胀性。将这些基本关系与循环荷载下砂土的物态变化相联系,建立了砂土的物态动本构关系。     

砂土应力路径本构模型的试验验证

建立了砂土应力路径本构模型,揭示了应力路径影响砂土应力-应变关系的本质,在平均应力p变化不大的条件下主要是剪应力比的影响。当使用该模型计算应力-应变关系时,将应力路径线性化,分别计算等平均应力p路径和等应力比 路径上的应变。利用试验对模型所引用的关系式 进行验证,试验结果和 的理论值较为吻合,证明了模型引用关系式 的合理性。并利用模型对复杂路径下砂土的应力-应变关系进行预测,对模型预测与试验结果进行比较,结果表明模型可以合理地考虑复杂应力路径对砂土应力-应变关系的影响。     

加筋土本构模型研究进展

概括了加筋土理论计算的分析方法 ,对采用复合模型进行研究所必须的加筋土本构模型的进展进行综述 ,综合分析了各种加筋土本构模型的适用条件和局限性 ,提出了今后加筋土本构模型研究的重点     

剪胀性砂土本构模型的研究

对于中密砂和密砂,剪胀现象是一个比较显著的特征,相变线是描述剪胀现象的一条特征线,它比较容易确定。因此,以相变线作为状态参考线,提出并定义了一种状态参量,在已有弹塑性模型基础上,将状态参量引入剪胀方程和塑性硬化模量表达式中,建立了一个新的考虑砂土剪胀性的本构模型。该模型尤其适合于中密砂和密砂,对于松砂则退化为原弹塑性模型。模型形式较简单,包含9个材料参数,且比较容易确定。数值模拟结果与试验数据吻合较好。     

基于相变状态的砂土本构模型的研究

为了很好地描述砂土的应力应变特征,通常利用以临界状态孔隙比为基础的状态参数建立弹塑性本构关系,但是对于密砂排水试验,临界状态参数很难测到。相变状态作为一特征状态,相关参数较容易测得。因此,本文定义了以相变状态孔隙比为基础的状态参数,并引入砂土的剪胀和边界应力比表达式,建立砂土的弹塑性本构模型。最后,利用本文提出的模型参数得到的密砂模拟结果与试验结果相吻合,较好地反映了密砂的应变强化和软化力学特征。     

不同应力路径下砂土的神经网络弹塑性本构模型研究

基于多种应力路径下砂土的加载、卸载和再加载过程的三轴排水试验数据，研究了三种应力路径对屈服面的影响，其结果表明，不同应力路径对砂土的本构模型有着不可忽视的作用。在此基础上，建立了砂土的弹塑性神经网络模型，对相应路径下的本构关系进行了学习。实例分析表明，该模型能够很好地描述具体应力路径下的本构关系，神经网络建模方法具有方便、容错性强的特点，对岩土力学快速、高效数值方法的进一步发展具有重要的参考价值。同时，在这种弹塑性应力-应变关系中，笔者并没有使用塑性势函数，这在目前的弹塑性本构关系的建模中是一种新的尝试。     

考虑颗粒破碎的冻结砂土非线性本构模型研究

颗粒破碎是粒状材料在高应力状态下的一种基本现象。为了研究冻结砂土中颗粒破碎对应力应变关系的影响,将冻结砂土视为复合颗粒材料,忽略冰的压融,考虑内摩擦角随应力状态的变化,构建一个适用于冻结砂土的考虑颗粒破碎的非线性本构模型。构建过程分为三步,首先是基于三轴剪切前后颗粒分析对冻结砂土颗粒破碎模式和产生机理进行探讨;其次是基于考虑颗粒破碎的能量平衡方程,对冻土在三轴剪切试验过程中的颗粒破碎耗能进行分析,结果表明颗粒破碎耗能随轴向应变呈双曲线变化趋势;最后应用考虑颗粒破碎的剪胀方程修正沈珠江三参数非线性模型中的体积切线模量ν_t,得到一个考虑颗粒破碎的非线性本构模型,模型参数可以通过单轴压缩试验和常规三轴试验确定。将原模型和修正后模型的计算结果与控制温度为-6℃,围压为1 MPa、4 MPa、6 MPa、8 MPa和10 MPa时冻结砂土的试验结果进行对比,结果表明该模型能够较好的模拟冻结砂土从低围压到高围压的应变软化特征与剪胀特征。      

考虑损伤的节理本构模型

本文在弹塑性损伤的理论框架内,讨论了节理等地质间断面的本构模型。这个模型能够反映节理面的损伤弱化,扩容和弹性刚度劣化等复杂特性。这个模型的另一优点是,塑性变形增量与屈服面是非正交的,但本构矩阵具有对称性。这种对称性在岩石力学的理论研究和数值分析中是至关紧要的。     

一个基于热力学的土体本构模型

修正剑桥模型假设体积塑性功的一半转化为耗散能,一半转化为由塑性变形约束的自由能,但通常体积耗散能和塑性体积自由能并不相等。基于热力学理论,通过引进间隔应力比来表征体积塑性功和塑性体积自由能的比例关系,构建了一个土的体积硬化模型。由于岩土材料耗散函数与所处的应力状态有关,因此,需要应用非关联流动法则,修正剑桥模型是适合应用相关联流动法则的一个特例,也是所提出模型的一个特例。     

基于广义热力学的超固结土本构模型

基于广义热力学基本理论,通过考虑塑性剪切变形产生的能量一部分以塑性自由能的形式储存,并且该部分自由能与超固结度相关,结合修正剑桥模型的热力学函数形式建立了适用于超固结土的自由能函数和耗散函数。该耗散函数与当前应力状态无关,相关联流动法则仍然适用。由建立的耗散函数和自由能函数,推导了弹塑性本构关系的屈服函数、流动法则、硬化定律。通过4种不同超固结土的试验结果和计算结果进行比较,验证了模型的合理性。     

Constitutive modeling of inherent anisotropy in a strain space multiple mechanism model for granular materials

Consideration of fabric anisotropy is crucial to gaining an improved understanding of the behavior of granular materials. This paper presents a constitutive model to describe the sand behavior associated with fabric anisotropy within a framework of a strain space multiple mechanism model. In the proposed model, a second-order fabric tensor is extended by incorporating a new function that represents the effect of inherent (or initial fabric) anisotropy, along with three additional parameters: two of them, a₁ and a₂ , control the degree of anisotropy, and the second mode of inherent anisotropy can be expressed by introducing the parameter a₂ as well as the first mode by the parameter a₁ . The third parameter, θ₀ , expresses the principal direction of inherent anisotropy (eg, the normal vector direction of bedding planes relative to horizontal axis). The formulation of the dilative component of dilatancy (ie, positive dilatancy) is also extended to consider the effect of inherent anisotropy based on the interlocking mechanism. Experimental data on the complex anisotropic responses of Fraser River sand and Toyoura sand under monotonic loading is used to validate this model. The proposed model is shown to successfully capture anisotropic responses, which become contractive or dilative depending on different principal-stress directions, with a single set of anisotropy parameters; thus, the model is considered to possess the capability to simulate the anisotropic behaviors of granular materials. In addition to different loadings on the same fabric, the effects of different fabric anisotropies upon the sand behavior under the same loadings are also investigated.     

On generalization of constitutive models from two dimensions to three dimensions

In this paper, a study is made of the generalization of constitutive models for geomaterials from two‐dimensional stress and strain states to three‐dimensional stress and strain states. Existing methods of model generalization are reviewed and their deficiencies are highlighted. A new method is proposed based on geometries of the model imprints on two normal planes. Using the proposed method, various three‐dimensional failure criterions suitable for geomaterials are implemented directly into a two‐dimensional model and the generalized model is identical to its original form for the axially symmetric condition. To demonstrate the application of the proposed method, the Modified Cam Clay model is extended using the Matsuoka–Nakai failure criterion. Simulations of soil behaviour for loading in the principal stress space are presented and analysed. Copyright © 2008 John Wiley & Sons, Ltd.     

Micromechanical analysis of failure propagation in frictional granular materials

The extent to which the evolution of instabilities and failure across multiple length scales can be reproduced with the aid of a bifurcation analysis is examined. We adopt an elastoplastic micropolar constitutive model, recently developed for dense cohesionless granular materials within the framework of thermomicromechanics. The internal variables and their evolution laws are conceived from a direct consideration of the dissipative mechanism of force chain buckling. The resulting constitutive law is cast entirely in terms of the particle scale properties. It thus presents a unique opportunity to test the potential of micromechanical continuum formulations to reproduce key stages in the deformation history: the development of material instabilities and failure following an initially homogeneous deformation. Progression of failure, initiating from frictional sliding and rolling at contacts, followed by the buckling of force chains, through to macroscopic strain softening and shear banding, is reproduced. Bifurcation point, marking the onset of shear banding, occurred shortly after the peak stress ratio. A wide range of material parameters was examined to show the effect of particle scale properties on the progression of failure. Model predictions on the thickness and angle of inclination of the shear band and the structural evolution inside the band, namely the latitudinal distribution of particle rotations and the angular distributions of contacts and the normal contact forces, are consistent with observations from numerical simulations and experiments. Copyright © 2009 John Wiley & Sons, Ltd.     

岩土本构模型的数学基础与广义位势理论

对于种类繁多的岩土材料的本构模型,认识其数学基础及假设以及相关的物理意义是深刻理解和正确使用它们的基础。在本文中,揭示了目前在岩土工程中现有的不同类型的本构模型的数学基础和假设及其联系;指出了其基本的问题是其中应力（应变）或者其增量是否为一有势场的梯度矢量。同时涉及到应力与应变及其增量的主轴是否相同;有势场的梯度矢量的旋度是否为零;刚度（柔度）矩阵是否对称及其秩是否为1等。还提出了广义位势理论：可以用唯一的势函数,也可以任意设立2个或者3个其梯度矢量线性无关的势函数,用它们的梯度矢量表示应力（应变）或者其增量及塑性应变增量,用简单的试验确定参数。对于具有极其复杂力学性质的岩土材料,广义位势理论为建立统一的岩土理论模型提供了基础。关 键 词：岩土本构模型;有势场;广义位势理论     

A micromechanically derived anisotropic micropolar constitutive law for granular media: Elasticity

In the present work, it is attempted to derive a macroscopic constitutive law for the elastic deformation of granular materials, based on microscopic considerations. For the sake of simplicity, the solution is restricted to two dimensions, that is, a random assembly of infinitely extended cylinders. After examining pairwise contact interactions, the elastic energy rate of the assembly is retrieved in a discrete form. Introducing the probability density function of the contact orientations, the continuum form of the elastic energy density rate is evaluated as a function of generalized strains and curvatures, and their rates. The stresses and couple stresses result as dual variables to the generalized strain and curvature rates. Some properties of the resulting model are discussed, examples are presented and conclusions are drawn.Copyright © 2014 John Wiley & Sons, Ltd.     

Description of deformation process in inherently anisotropic granular materials

The main focus in this work is on modeling of mechanical response of granular materials that display inherent anisotropy. Both the experimental and numerical investigations are described. First, the results of direct shear as well as drained/undrained triaxial tests that involve crushed limestone with elongated angular‐shaped particles are reviewed. Afterward, a mathematical framework is presented for modeling of elastic/ inelastic deformation that incorporates the multi‐laminate approach. The deformation is monitored on a set of randomly oriented planes, and the formulation incorporates the thickness of the shear band that is associated with sliding/separation process. A systematic procedure for identification of material functions/ parameters is outlined that is based on the results of direct shear tests, and the framework is later applied to simulate the behavior under triaxial conditions. The results of numerical simulations are compared with the experimental data. Copyright © 2011 John Wiley & Sons, Ltd.     

基于颗粒组构特性的散体材料本构模型研究

通过散体介质材料单元颗粒排列组构表达的细观结构力学关系,建立了用颗粒密集度、颗粒排列组构关系和颗粒间摩擦特性等非连续介质材料特性参数描述的散体介质材料本构模型,从而实现散体介质材料宏观连续介质描述的等效应力表达.通过该模型可采用数值方法进行散体介质材料准静态情况下的力学特性分析.文中最后基于有限元软件ABAQUS,进行了该本构模型的二次开发.数值算例结果验证了所建立散体介质材料本构模型的适用性.     

模拟土体本构特性的热力学方法

简要介绍了建立岩土材料弹塑性本构模型的热力学方法。它不仅具有紧凑的数学结构,而且自动满足热力学定律,仅从两个热力学势函数,即自由能函数与耗散增量函数出发,就足以导出弹塑性理论必须的屈服条件,流动法则,硬化定律和弹性定律。通过理论证明指出,只要耗散增量函数依赖于当前应力,流动法则必然是非关联的,岩土材料的摩擦特性与非关联流动法则密不可分。介绍该方法在三维模型,岩土材料的微细观力学特性,应力应变的均匀化以及剪胀和各向异性方面应用的主要研究进展,并对一些重要的概念,诸如“储存的塑性功”,“Reynolds-Taylor状态”等,进行分析与解释。最后给出近期需进一步深入研究的几点建议。     

亚塑性理论简介

简要介绍了亚塑性理论和亚塑性本构模型以及在颗粒材料力学分析上的应用。详细地介绍了亚塑性模型参数的确定方法。亚塑性本构模型不是从弹塑性理论发展而来,它是以非线性张量为基础,没有屈服面、塑性势、流动法则、硬化定律以及把变形分解为弹性和塑性部分等概念。亚塑性在很多方面具有一定的优越性,特别是涉及到应力水平非常低或者非常高的情况。     

膨胀土弹塑性本构关系数值建模方法研究

按照数值建模理论,建立了不同含水率条件下膨胀土的应力-应变关系。通过可视化绘出了在整个应力场（p,q）中的三维应力-应变关系曲面和屈服轨迹。经过对比可见含水率的变化对膨胀土本构关系的影响是明显的。未使用传统的塑性势理论,而是采用数值建模方法,既克服了寻找塑性势解析表达式的困难,又可以任意选择含水率等初始条件,从而使建立的本构数值模型能够真实地反映膨胀土的变形过程