非饱和膨胀土的结构损伤模型及其在土坡多场耦合分析中的应用

针对原状膨胀土对气候变化反映敏感的特点和其具有胀缩性、裂隙性、超固结性等力学特性,以非饱和土力学和损伤力学为基础,建立了一个非饱和膨胀土的弹塑性损伤本构模型及相应的固结模型．把原状膨胀土看成是由未损部分和损伤部分的复合体,未损部分用非饱和土的非线性本构关系描述,损伤部分用损伤演化方程和两个屈服面（即,加载屈服面和剪切屈服面）描述．其中的损伤演化方程包括加载引起的损伤和干湿循环引起的损伤两个方面,用作者研制的CT-三轴试验确定．设计了相应的有限元程序UESEPDC;对非饱和膨胀土边坡进行了三相多场耦合问题的数值分析．分析分为4个阶段,得到了边坡在每一分析阶段的应力场、位移场、孔隙水压力场、孔隙气压力场、含水量场、基质吸力场、结构损伤演化场和塑性区扩展的动态图,较好地揭示了膨胀土边坡在开挖和气候变化条件下逐渐发生失稳滑动的现象及其机理．     

岩土材料弹塑性正交异性损伤耦合本构理论

在不可逆热力学框架内建立了岩土材料的正交异性损伤塑性耦合宏观唯象本构理论。主要结果有：1）给出了耦合的塑性和损伤的演化律;2）从对含裂纹单元的细观分析入手,通过均匀化（Homogenization）处理,将损伤引入到Mohr-Coulomb条件下,模型同时考虑了损伤对剪切强度及摩擦角的影响,扩容现象则通过损伤应变来计算。     

高温作用下混凝土热-水-力耦合损伤分析模型

以混合物理论为基础建立了高温作用下混凝土的热-水-力耦合损伤分析模型．将混凝土视为由固体骨架、液态水、水蒸气、干燥气体和溶解气体共5种组分构成的混合物,模型的宏观平衡方程包括各组分的质量守恒方程、整体的能量守恒方程及动量守恒方程,模型所需的状态方程及本构关系全部给出,最后给出基于4个主要参数（固体骨架位移、气压力、毛细压力和温度）的控制方程．模型考虑了混凝土在高温作用下,水分的蒸发与冷凝、胶结材料的水化及脱水、溶解气的溶解与挥发等相变过程;从材料变形破坏过程中能量耗散特征入手,基于Lemaitre应变等价性假说和能量守恒原理得到力学损伤演化方程,并考虑了高温引起的热损伤对材料力学性能及力学损伤演化规律的影响,建立了热-力耦合损伤本构模型．     

双重孔隙渗流作用井眼围岩损伤力学模型研究

考虑双重介质建立了井眼围岩力学模型,考虑井眼围岩岩体为孔隙、裂缝双重介质,将围岩区域分为破坏区、损伤区和弹性区,建立双重介质渗流作用下的井壁围岩不同区域的损伤力学计算模型和井眼损伤区域的计算方法,计算结果表明理论计算模型与有限元模拟结果吻合较好.     

含液体非弹性多孔介质中波传播过程的失稳与逸散性

在基于Biot理论的饱和-非饱和多孔介质的动力-渗流模型中计及流固惯性耦合效应。对单轴应变的一维情况讨论了饱和和非饱和多孔介质中波传播过程的驻值失稳和逸散性,分析了流固粘性耦合,流固惯性耦合,流固混合体的压缩性,孔隙水饱和度,及固体骨架在高应变速率下材料粘弹塑性本构行为等因素的影响。该工作将对克服饱和与非饱和多孔介质在强动荷载下波传播过程的数值求解困难提供理论上的依据和启示。     

有限变形下的混凝土动态本构关系研究

讨论有限变形和小变形假设下本构关系的区别,并将其运用于混凝土的弹-粘塑性本构关系研究,提出了一个应变率相关的动态力学模型．模型基于Ottosen的4参数屈服准则,分别考虑混凝土在硬化阶段和软化阶段加载面的不同变化规律,建立冲击荷载下的混凝土本构关系．该模型可以应用于冲击载荷下混凝土材料响应的模拟．引进Green-Naghdi客观率建立有限变形的混凝土模型．根据大量实验结果对应变率和材料强度的关系提出合理假设,使模型可以反映混凝土大变形的动态力学行为,为相关工程问题的研究提供有益的思路和有效的工具．     

脆性材料损伤应变软化的数学模型

本文提出一种脆性材料损伤应变软化的数学模型，本构方程是基于热力学原理建立的。虽然是各向同性损伤模型，用标量表示损伤状态，但通过等效损伤应变的定义，能区分拉伸、压缩和剪切载荷对材料损伤的不同响应。由于本构模型中的多数参数均可由材料材料手册简单确定，便于工程应用。     

Ⅰ阶梯度损伤理论

从热力学基本定律出发,将应变张量、标量损伤变量、损伤梯度作为Helmholtz自由能函数的状态变量,利用本构泛函展开法在自然状态附近作自由能函数的Taylor展开,未引入附加假设,推导出Ⅰ阶梯度损伤本构方程的一般形式．该形式在损伤为0时可退化为线弹性应力-应变本构方程,在损伤梯度为0时可退化为基于应变等效假设给出的线弹性局部损伤本构方程．一维解析解表明,随着应力增大,损伤场逐步由空间非周期解变为关于空间的类周期解,类周期解的峰值区域形成局部化带．局部化带内的损伤变量将不同于局部化带外的损伤变量,由此可以反映出介质的局部化特征．损伤局部化并不是与损伤同时发生,而是在损伤发生后逐渐显现出来,模型的局部化机制开始启动;损伤局部化的宽度同内部特征长度成正比．     

各向同性弹性损伤本构方程的一般形式

直接从不可逆热力学基本定律出发,推导出弹性各向同性损伤材料本构方程的一般形式,克服了由应变等效假设建立的经典损伤本构方程的缺陷,并阐明了两种各向同性弹性损伤模型(单标量模型与双标量模型)之间的联系.研究表明,采用单标量描述的损伤模型,在材料损伤本构方程中含有两个“损伤效应函数”,反映损伤对于两个弹性常数的不同影响.应变等效假设给出的损伤本构方程,是该文方程的一个近似形式,常常不能满意地描述实际材料的损伤行为.     

韧性材料中的一个新的动态孔洞增长模型

本文提出了一个可用来描述韧性材料动态断裂过程的新模型.基体是由具有过应力形式的弹-粘塑性本构关系的材料构成.文中给出了在常等效应变率下的含孔洞材料的动态加载面及其相应的近似解析表达式.当材料单元经受球对称载荷作用时,本文的模型将退化为Carroll-Holt-Johnson模型.当材料的应变率敏感参数趋于零时,本文模型将退化为Gurson模型.本文的研究还表明,在一般情况下正交性法则是不成立的.最后,将本文模型与近年来Pan,Saje,Needleman和Perzyna等人所提出的含孔洞材料的粘塑性本构模型进行了比较.     

New damage evolution model of rock material

As a kind of natural engineering material with original defects, there are distinctly nonlinear and anisotropic mechanical behaviors for rock materials. Nevertheless, the rock damage mechanics can solve this problem well. However, for the complexity of mechanical property of rock material, the mature and applicable model to describe the rock failure process and the method to determine the maximum damage value have not been established very well. To solve this problem, one new damage evolution model for rock material has been proposed. In this model, the least energy consumption principle proposed to describe the fracture process of materials is used. Using the experimental data of granite sample under uniaxial compression and the results of numerical tests under uniaxial tension and uniaxial compression, this model is verified. Moreover, the results of the new model have been compared with the results of the tests (numerical test and real test) and the traditional damage model. The comparison shows that the new model has the higher accuracy and better reflects for the fracture process of the granite sample. Moreover, the released damage energies of the new model and Mazars model are different, and the released damage energy of the new model is slightly less than that of the Mazars model.     

A Theoretical Model and Experimental Investigation of a Nonlinear Constitutive Equation for Elastic Porous Metal Rubbers

Starting from the theory of porous materials, the nonlinear theory of dry friction, and the model of a bent slender beam, a nonlinear constitutive equation for elastic porous metal rubbers is constructed. Static compressive experiments were carried out on hollow cylinders of such a rubber, from which relations between all coefficients of the constitutive equation and the material density were determined. Based on the data obtained, the constitutive equation of the material was predicted successfully. The effect of density of the metal rubber on its stiffness and on the nonlinear constitutive equation was revealed by experiments.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 4, pp. 449–460, July–August, 2005.     

On the heat flux vector for flowing granular materials—part II: derivation and special cases

Heat transfer plays a major role in the processing of many particulate materials. The heat flux vector is commonly modelled by the Fourier's law of heat conduction and for complex materials such as non‐linear fluids, porous media, or granular materials, the coefficient of thermal conductivity is generalized by assuming that it would depend on a host of material and kinematical parameters such as temperature, shear rate, porosity or concentration, etc. In Part I, we will give a brief review of the basic equations of thermodynamics and heat transfer to indicate the importance of the modelling of the heat flux vector. We will also discuss the concept of effective thermal conductivity (ETC) in granular and porous media. In Part II, we propose and subsequently derive a properly frame‐invariant constitutive relationship for the heat flux vector for a (single phase) flowing granular medium. Standard methods in continuum mechanics such as representation theorems and homogenization techniques are used. It is shown that the heat flux vector in addition to being proportional to the temperature gradient (the Fourier's law), could also depend on the gradient of density (or volume fraction), and D (the symmetric part of the velocity gradient) in an appropriate manner. The emphasis in this paper is on the idea that for complex non‐linear materials it is the heat flux vector which should be studied; obtaining or proposing generalized form of the thermal conductivity is not always appropriate or sufficient. Copyright © 2006 John Wiley & Sons, Ltd.     

Numerical investigation of seismic attenuation in fluid-saturated fractured media: An extended view of the Skempton coefficient

The interpretation of data from seismic exploration gains from consideration of hydro-mechanical processes in particular when the waves propagate through fluid-filled fractured porous rocks. We specifically investigate attenuation processes in porous rock containing complex fracture networks with the main objective to identify effective hydro-mechanical material properties by computational homogenization. To this end, we generate stochastic fracture ensembles and approximate fractures as ellipses with low aspect ratio (1/100). In other words, the fractures constitute thin and long hydraulic conduits with high permeability. Full periodic boundary conditions are employed on the small scale. We observe a strongly heterogeneous pressure propagation in the fracture network and the surrounding rock. The properties of the macroscopic substitute model are derived by means of a volume averaging technique. We identify a dependence of effective properties on fluid saturation and amount of fractures. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the heat flux vector for flowing granular materials—Part I: effective thermal conductivity and background

Heat transfer plays a major role in the processing of many particulate materials. The heat flux vector is commonly modelled by the Fourier's law of heat conduction and for complex materials such as non‐linear fluids, porous media, or granular materials, the coefficient of thermal conductivity is generalized by assuming that it would depend on a host of material and kinematical parameters such as temperature, shear rate, porosity or concentration, etc. In Part I, we will give a brief review of the basic equations of thermodynamics and heat transfer to indicate the importance of the modelling of the heat flux vector. We will also discuss the concept of effective thermal conductivity (ETC) in granular and porous media. In Part II, we propose and subsequently derive a properly frame‐invariant constitutive relationship for the heat flux vector for a (single phase) flowing granular medium. Standard methods in continuum mechanics such as representation theorems and homogenization techniques are used. It is shown that the heat flux vector in addition to being proportional to the temperature gradient (the Fourier's law), could also depend on the gradient of density (or volume fraction), and D (the symmetric part of the velocity gradient) in an appropriate manner. The emphasis in this paper is on the idea that for complex non‐linear materials it is the heat flux vector which should be studied; obtaining or proposing generalized form of the thermal conductivity is not always appropriate or sufficient. Copyright © 2006 John Wiley & Sons, Ltd.     

Thermo-poroacoustic acceleration waves in elastic materials with voids

A model for coupled elasto-acoustic waves, thermal waves, and waves associated with the voids, in a porous medium is investigated. Due to the use of lighter materials in modern buildings and noise concerns in the environment such models for thermo-poroacoustic waves are of much interest to the building industry. Analysis of such waves is also of interest in acoustic microscopy where the identification of material defects is of paramount importance to industry and medicine. We present a model for acoustic wave propagation in a porous material which also allows for propagation of a thermal wave. The thermodynamics is based on an entropy inequality of A.E. Green, F.R.S. and N. Laws and is presented for a modification of the theory of elastic materials with voids due to J.W. Nunziato and S.C. Cowin. A fully nonlinear acceleration wave analysis is initiated.     

基于L-D流动法则模糊弹粘塑性的有限变形分析

为了进行岩土材料有限变形的动力分析,采用Green应变和第二类Kirchoff应力描述材料的几何非线性。将隶属度函数引入到屈服函数中,并采用L-D屈服准则,得到了基于L-D流动法则的模糊弹粘塑性本构模型。应用非线性有限元原理,得到了土样动三轴实验有限变形的数值结果,并与小变形的数值结果和土样的动三轴实验结果进行了对比。通过对比发现有限变形的结果更加接近动三轴的实验结果,且模糊弹粘塑性模型能很好地反映循环荷载作用下岩土的动力性质,是岩土动力分析的一种有效方法.