INFLUENCE OF DISPLACEMENT OF SATURATED SAND STRATUM ON PRE-STRESSED ANCHORS

土层变形是造成预应力值波动甚至失效的重要原因. 利用载荷位移传递函数,基于弹性理论建立了饱和粉细砂层变形过程中锚索受力模型,通过实例研究了锚索预应力值在施工过程中的变化规律及锚固体在地层变形中的受力特性,结果表明锚固体接触面剪切刚度,锚索倾斜角度以及锚固体直径都是影响锚固体内力及接触面剪切应力的重要因素,为类似的预应力锚索支护工程的设计施工提供经验.     

三维编织复合材料渐进损伤的非线性数值分析

基于考虑纤维束相互挤压的八边形纤维束截面单胞模型，引入周期性位移边界条件，采用 细观非线性有限元方法，建立了三维四向编织复合材料的渐进损伤拉伸强度模型. 该模型考 虑了增强体纤维束纵向非线性剪切应力-应变关系，采用Hashin型损伤失效准则定义了纤维 束的典型损伤类型，并根据纤维束和纯基体相应损伤类型所造成的材料性能退化，模拟了不 同编织角试件各类损伤产生、扩展及材料最终破坏的整个过程. 模型数值结果与实验数据吻 合较好，证明了该模型的合理有效性. 探讨了组分材料剪切非线性、损伤对材料宏观非线性 本构行为的影响，结果表明：随着编织角增大，纤维束剪切非线性效应和累积损伤对材料非 线性力学行为的影响明显增强.     

结构与土接触面的弹黏塑性本构模型

基于Goodman接触面单元,在Clough--Duncan双曲线关系式的基础上改进了三元件宾厄姆体,建立了结构与土接触面的弹黏塑本构模型,使用ABAQUS的FRIC子程序对该模型进行了二次开发.通过改装的应力控制式结构-土接触面剪切试验仪进行了接触面长期剪切试验,验证了该接触面本构模型.研究结果表明:结构与土接触面的弹黏塑本构模型能较好地模拟接触面的力学特性和时间效应;正应力对结构与土接触面的力学行为影响较大,正应力越大,接触面的时间效应越显著.     

混凝土三维细观接触面模型数值模拟与CT试验验证

对混凝土三维随机骨料模型进行了改进,在骨料和砂浆之间加入了"面-面接触单元"模拟两者的接触特性,编制了相应的命令程序,称新模型为混凝土接触面模型.采用双折线损伤演化模型进行计算,对数值模拟结果进行了分析研究.从混凝土破坏过程图和荷载-位移曲线图两方面与CT试验结果进行了比较,表明试件破坏时裂纹的萌生、扩展过程与CT试验...     

平纹编织陶瓷基复合材料面内剪切细观损伤行为研究

采用约西佩斯库(Iosipescu)纯剪切试件,研究了平纹编织SiC/SiC和C/SiC复合材料的面内剪切应力-应变行为和细观损伤特性.通过试验获得了材料不同方向上的单调和迟滞应力-应变行为,对比分析了两种材料的剪切损伤特性,结果表明材料的剪切损伤演化规律受热残余应力水平影响严重.由试件断口电镜扫描结果发现剪切加载状态下桥连纤维承受显著的弯曲载荷和变形,据此提出了纤维弯曲承载机制,并结合裂纹闭合效应分阶段阐释了材料的剪切迟滞环形状.基于材料的剪切细观损伤机制,通过两个损伤变量表征了材料的剪切损伤演化进程,得到了材料的面内剪切细观损伤演化模型.对比发现2D-C/SiC复合材料45°方向基体裂纹的起裂应力明显小于2D-SiC/SiC复合材料,而两者0°/90°方向裂纹的起裂应力基本相同.      

全长锚固锚杆锚固单元力学性能实验研究

锚固单元的传力特性是影响全长锚固锚杆支护能力的重要因素。由于锚固单元界面构成复杂，本文主要考虑锚杆与粘结材料及其界面的力学特性，开展锚固单元界面剪切力学实验研究。实验结果表明，砂浆强度直接影响界面的峰值强度和剪切刚度；采用相同强度砂浆，界面的峰值强度、剪切刚度和残余剪切强度都与法向应力成正比；在相同法向应力作用下，剪切速率增加引起峰值剪切强度增大，但对残余剪切强度影响较小。依据实验剪切应力–位移曲线将锚固单元与岩石间界面的解耦过程分为“峰前–软化–滑移”三阶段，非连续变形分析方法数值模拟结果表明，加载初期的损伤主要受粘结材料抗拉强度的影响，临近峰值阶段与粘结材料张剪混合破裂相关；软化阶段和滑移阶段主要受粘结材料剪切特性和颗粒形状的影响；引入实验所获得的三线滑移模型曲线到全长锚固锚杆模型，模拟拔出数值实验结果表明较快拔出速率将影响锚杆变形能力。     

粗粒土与结构接触面受载过程中的损伤

进行了粗粒上与结构接触面单调和循环加载试验,基于宏细观测量结果,扩展了损伤概念以描述该类接触面在受载过程中的物态演化,及由于物态演化导致的力学特性从初始状态到最终稳定状态的连续变化过程.揭示了接触面损伤的细观物理基础主要是接触面内土的颗牲破碎和剪切压密这两种物态演化;指出接触面的剪胀体应变可以划分为可逆性和不可逆性剪胀体应变两部分,其中不可逆性剪胀体应变可作为接触面损伤发展的宏观量度,因此其归一化形式可作为一种损伤因子的定义;提出了建立粗粒土与结构接触面一种损伤本构关系的基本思路.     

Cosserat连续体模型中本构参数对应变局部化模拟结果影响的数值分析

基于所发展的压力相关弹塑性Cosserat连续体模型及相应的数值方法,以一维剪切层及二维平板压缩问题为例,数值分析了Cosserat连续体模型中的本构参数Cosserat剪模、软化模量及内部长度参数对应变局部化数值模拟结果的影响.结果表明在一定取值范围内,Cosserat剪模对数值模拟结果几乎没有影响,并给出了具体数值计算时的取值范围;软化模量绝对值越大,后破坏段的荷载-位移曲线越陡,计算得到的剪切带宽度越窄;内部长度参数越大,后破坏段的荷载-位移曲线越平缓,计算得到的剪切带越宽.     

含随机参数的非线性黏弹性有限元计算

进行了粗粒土与结构接触面单调和循环加载试验，基于宏细观测量结果, 扩展了 损伤概念以 描述该类接触面在受载过程中的物态演化, 及由于物态演化导致的力学特性从初始状态到最终 稳定状态的连续变化过程. 揭示了接触面损伤的细观物理基础主要是接触面内土的颗粒破碎 和剪切压密这两种物态演化；指出接触面的剪胀体应变可以划分为可逆性和不可逆性剪胀体 应变两部分，其中不可逆性剪胀体应变可作为接触面损伤发展的宏观量度，因此其归一化 形式可作为一种损伤因子的定义；提出了建立粗粒土与结构接触面一种损伤本构关系的基本思路.     

海洋系泊链钢22MnCrNiMo腐蚀磨损试验与数值分析研究

建立了锚链在海洋环境中腐蚀磨损(简称"磨蚀")累积损伤数值分析方法,该方法采用非线性有限元分析,能够同时考虑锚链链环间接触面在海水中的腐蚀和磨损耦合损伤。针对22MnCrNiMo低碳低合金钢材料,进行了力学性能、海水侵蚀以及磨蚀性能等多方面的试验研究,确定了基于该材料的锚链链环间接触面在海水中磨蚀损伤数值分析中的相关参数。通过对计算结果与试验结果的比较分析,验证了锚链链环间接触面磨蚀累积损伤数值分析方法的可行性与准确性。     

Shear failure of tungsten alloy at mesoscale modeled by Movable cellular Automata

Shear failure and deformation localization are studied for tungsten alloy undergoing impact failure and “self-sharpening” in ordnance. Movable cellular Automata (MCA) method is employed to simulate the interior-structure of tungsten alloy such that shear deformation failure at mesoscale level under shear loading can be analyzed. The results show that the velocity of every automaton would vary continuously with deformation. A large velocity vortex sweeping throughout the specimen occurs at the initial loading stage. This corresponds to uniform deformation. Subsequently, the deformation adopts a pattern with more localized vortices. The vortex-morphology would change continually to sustain the global deformation field. The contact between the local vortices induces stress concentration. This means that the deformation of certain automaton pairs would not accommodate the equilibrium of vortex rotation. The different mechanisms of micro-damage mechanisms along the interface between the W grain and matrix are developed quickly throughout the whole specimen. Such shear instability leads to failure. It is also shown that the W grain size effect is sufficient to cause premature shear deformation instability of the tungsten alloy, even at low shear stress.     

Mechanisms of stress transfer and interface integrity in carbon/epoxy composites under compression loading: Part I: Experimental investigation

Raman spectroscopy is used to get an insight into the microstructural aspects of the compressional behavior of carbon fiber composites. This is done by a comparative assessment of the stress transfer efficiency in tension and compression in single-fiber discontinuous model geometries. It was found that axial stress is transferred in the fiber through the generation of shear stresses at the interface for both tension and compression loading. Experimental evidence is presented to verify that the values of the maximum interfacial shear stress that the system sustains is a function of the applied strain and independent of the type of loading. However, compressive failure is quite different as fiber fragments remain in contact, thus can still bear load.     

岩体—界面系统剪切不稳定性分析

基于界面的刚塑性应变软化假设，分析了岩体－界面系统在端部剪力和岩体中分布剪切载荷共同作用下的变形、应力和损伤演化。利用位能原理和稳定性的能量准则，得到了岩体界面系统的不稳定性条件。分析结果表明，损伤区达到边界之前，系统可能是稳定的或者是不稳定的。依赖于分布剪切载荷和界面摩擦力的比较，若均布剪切载荷大于界面摩擦力，则系统不稳定，否则系统稳定；当损伤区达到边界之后，系统的不稳定性决定于载荷及界面材料性质，界面软化刚度系数和界面强度对于不稳定性有明显影响。     

Opening and contact zones of an interface crack in a piezoelectric bimaterial under combined compressive-shear loading

A plane problem for a tunnel electrically permeable interface crack between two semi-infinite piezoelectric spaces is studied. A remote mechanical and electrical loading is applied. Elastic displacements and potential jumps as well as stresses and electrical displacement along the interface are presented using a sectionally holomorphic vector function. It is assumed that the interface crack includes zones of crack opening and frictionless contact. The problem is reduced to a combined Dirichlet–Riemann boundary value problem which is solved analytically. From the obtained solution, simple analytical expressions are derived for all mechanical and electrical characteristics at the interface. A quite simple transcendental equation, which determines the point of separation of open and close sections of the crack, is found. For the analysis of the obtained results, the main attention is devoted to the case of compressive-shear loading. The analytical analysis and numerical results show that, even if the applied normal stress is compressive, a certain crack opening zone exists for all considered loading values provided the shear field is present. It is found that the shear stress intensity factor at the closed crack tip and the energy release rates at the both crack tips depend very slightly on the magnitude of compressive loading.     

土的工程力学性质的颗粒流模拟

基于颗粒流理论,引入不同的颗粒接触连接本构模型,分别建立了砂土和粘性土的颗粒流模型．通过颗粒流数值模型试验,对砂土和粘性土的室内平面应变试验及其剪切带形成和发展进行了数值模拟,分别对比了不同围压下颗粒流试样与室内试验的应力应变关系曲线,基本再现了砂土和粘性土试样应力．应变关系．通过砂土和粘性土PFC试样剪切带模拟表明,当围压较小时试样内部颗粒位移量小而且分布范围较广,当围压增大时,试样内部颗粒位移量也增大,而且发生较大位移颗粒的分布范围趋于集中,同时随着围压的增大试样内部形成明显的剪切带．无论砂土还是粘性土的PFC试样,随着围压的增加剪切带的形状趋于集中,而且剪切带宽度在减小．在围压很小时,试样内形成大的破坏区域,在围压较大时出现明显的线破坏区．这些规律基本与室内试验结果相似。     

Interface crack with a contact zone in an isotropic bimaterial under thermomechanical loading

A plane problem for a thermally insulated interface crack with a contact zone in an isotropic bimaterial under tension–shear mechanical loading and a temperature flux is considered. The expressions for the stresses and the electrical flux as well as for the derivatives of the displacement and the temperature jumps at the material interfaces via sectionally holomorphic mechanical and thermal potential functions are given. After the solution of the thermal problem the inhomogeneous combined Dirichlet–Riemann boundary value problem is formulated and solved exactly. The stresses at the interface and the stress intensity factors at the singular points are presented in a clear analytical form. Special attention is devoted to the case of a small contact zone when the stress intensity factors can be presented in form similar to the associated presentation for an “open” crack model. A transcendental equation and an asymptotic analytic formula for the determination of the real contact zone length are derived. It is shown that for a certain bimaterial this length as well as the correspondent stress intensity factor are defined by a single parameter which depends on the normal-shear loading and the heat flux.     

A BEM solution to transverse shear loading of composite beams

In this paper a boundary element method is developed for the solution of the general transverse shear loading problem of composite beams of arbitrary constant cross-section. The composite beam consists of materials in contact, each of which can surround a finite number of inclusions. The materials have different elasticity and shear moduli with same Poisson’s ratio and are firmly bonded together. The analysis of the beam is accomplished with respect to a coordinate system that has its origin at the centroid of the cross-section, while its axes are not necessarily the principal ones. The transverse shear loading is applied at the shear centre of the cross-section, avoiding in this way the induction of a twisting moment. Two boundary value problems that take into account the effect of Poisson’s ratio are formulated with respect to stress functions and solved employing a pure BEM approach, that is only boundary discretization is used. The evaluation of the transverse shear stresses is accomplished by direct differentiation of these stress functions, while both the coordinates of the shear center and the shear deformation coefficients are obtained from these functions using only boundary integration. Numerical examples with great practical interest are worked out to illustrate the efficiency, the accuracy and the range of applications of the developed method. The accuracy of the proposed shear deformation coefficients compared with those obtained from a 3-D FEM solution of the ‘exact’ elastic beam theory is remarkable.     

纤维增强韧性基体界面力学行为

分析了纤维增强韧性基体的界面力学行为及其失效机理,按剪滞理论和应变理化规律研究微复合材料的弹塑性变形和应力状态,讨论了幂硬化和线性硬化基体的弹塑性变形和界面应力分布,并给出纤维应力和位移的表达式。按最大剪应力强度理论建立了纤维／基体界面失效准则,推导出弹塑性界面失效的平均剪应力随纤维埋入长度的变化关系。     

压缩剪切测试中载荷传递行为的数字光弹性研究

结合光弹性四步彩色相移法,提出改进的六步相移法来计算全场剪应力,对径压缩圆盘实验证实了该方法的正确性,并进一步研究了同质材料连接结构在压缩剪切测试中的层间剪切行为。实验结果表明:全场等色线条纹级数和剪应力连续分布且随载荷而增加;中线附近剪应力趋于零,而条纹级数为峰谷。在连接界面上的条纹级数和剪应力出现峰值,特别是在连接界面端部为最高,在最大载荷下可分别达3.5级和2.4MPa,是导致连接界面脱粘开裂的危险区域。连接结构通过层间剪应力进行应力传递,在连接界面上剪应力与外载基本保持平衡。