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1.
Previous work on three‐dimensional shakedown analysis of cohesive‐frictional materials under moving surface loads has been entirely for isotropic materials. As a result, the effects of anisotropy, both elastic and plastic, of soil and pavement materials are ignored. This paper will, for the first time, develop three‐dimensional shakedown solutions to allow for the variation of elastic and plastic material properties with direction. Melan's lower‐bound shakedown theorem is used to derive shakedown solutions. In particular, a generalised, anisotropic Mohr–Coulomb yield criterion and cross‐anisotropic elastic stress fields are utilised to develop anisotropic shakedown solutions. It is found that shakedown solutions for anisotropic materials are dominated by Young's modulus ratio for the cases of subsurface failure and by shear modulus ratio for the cases of surface failure. Plastic anisotropy is mainly controlled by material cohesion ratio, the rise of which increases the shakedown limit until a maximum value is reached. The anisotropic shakedown limit varies with frictional coefficient, and the peak value may not occur for the case of normal loading only. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
2.
Thermoplasticity and strain localization in transversely isotropic materials based on anisotropic critical state plasticity 
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下载免费PDF全文 Geomaterials such as soils and rocks are inherently anisotropic and sensitive to temperature changes caused by various internal and external processes. They are also susceptible to strain localization in the form of shear bands when subjected to critical loads. We present a thermoplastic framework for modeling coupled thermomechanical response and for predicting the inception of a shear band in a transversely isotropic material using the general framework of critical state plasticity and the specific framework of an anisotropic modified Cam–Clay model. The formulation incorporates anisotropy in both elastic and plastic responses under the assumption of infinitesimal deformation. The model is first calibrated using experimental data from triaxial tests to demonstrate its capability in capturing anisotropy in the mechanical response. Subsequently, stress‐point simulations of strain localization are carried out under two different conditions, namely, isothermal localization and adiabatic localization. The adiabatic formulation investigates the effect of temperature on localization via thermomechanical coupling. Numerical simulations are presented to demonstrate the important role of anisotropy, hardening, and thermal softening on strain localization inception and orientation. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
3.
从土的各向异怀角度对土的可恢复剪胀现象进行了解释。基于各向异性情况下的土体弹性本构关系理论分析，认为土的可恢复剪胀现象可部分归因于土的各向异性引起的弹性剪胀。借助有关土体弹性参数实验结果，研究了应力诱导各迥异性对土体弹性剪胀的影响，结果表明：随土体应力诱导各向异性的增大，土体的弹性剪胀也增大。从土体弹性剪胀角度研究了土的卸荷体缩条件，认为土体卸荷体缩取决于加载应力路径的应力增量比，给出了土体出现卸荷体缩的区域。 相似文献
4.
通过室内三轴试验,研究了甘肃定西原状Q3黄土的各向异性对于黄土抗剪强度和变形参数的影响。研究结果表明,此种黄土的各向异性对土体力学性质的影响显著。垂直向原状黄土抗剪强度明显高于水平向,随着围压的增大,二者之差明显下降,最终稳定在10%的差值范围内。围压小于100 k Pa时,水平向破坏应变明显大于垂直向,且随着围压逐渐增大二者差值逐渐减小,并在围压高于200 k Pa时,破坏应变达到一致。利用邓肯-张模型对偏差应力实测值与计算值进行差值分析表明,低应变处垂直向与水平向的差值均较大;随着围压增大,差值逐渐减小并最终稳定在±5%差值范围内,且最大偏差应力均符合误差为±5%的范围。无论是垂直样还是水平样,大约在2%应变之前的应力应变曲线都近似为回归系数很高的线性关系,可近似估算不同方向黄土的变形模量,其值分别为130 MPa和85 MPa。 相似文献
5.
在临界状态弹塑性力学的框架内,建立了可以考虑循环荷载作用下各向异性对饱和软土力学特性影响的边界面塑性模型。该模型采用非关联的流动法则,引入了反映土体各向异性的内变量,利用该内变量的初始值描述初始各向异性,采用一种理论更为严谨、模型参数确定更为恰当的旋转硬化法则描述循环加载过程中各向异性的演化,利用更新映射中心的径向映射法则和与塑性偏应变路径长度有关的塑性模量插值规律,保证模型能够模拟循环加载时应力-应变响应的非线性、滞回性、应变累积性等基本特性,解释了模型参数的物理意义和确定方法,特别是给出了一种合理确定描述土体初始各向异性状态变量方法。通过文献中等压固结和偏压固结饱和黏土的循环三轴试验结果与模型预测结果的对比验证了模型的合理性。 相似文献
6.
A review of the literature indicates that the elastic behaviour of granular materials is isotropic and that Poissony's ratio is constant, whereas Young's Modulus, the bulk modulus and the shear modulus vary with the mean normal stress and the deviatoric stress. A nonlinear, isotropic model for the elastic behaviour is developed on the basis of theoretical considerations involving the principle of conservation of energy. Energy is therefore neither generated not dissipated in closed-loop stress paths or in closed-loop strain paths. The framework for the model consists of Hooke's law, in which Poission's ratio is constant and Young's modulus is expressed as a power function invlving the first invariat of the stress tensor and the second invariant of the deviatoric stress tensor. The characteristics of the model are described, and the accuracy is evaluated by comparison with experimental results from triaxial tests and three-dimensional cubical triaxial tests with a variety of stress paths. Parameter determination from unloading–reloading cycles in conventional triaxial compression tests is demonstrated, typical parameter values are given for granular materials and extension of the model to soils with effective cohesion is described. 相似文献
7.
Existing solutions to Mandel's problem focus on isotropic, transversely isotropic, and orthotropic materials, the last two of which have one of the material symmetry axes coincide with the vertical loading direction. The classical plane strain condition holds for all these cases. In this work, analytical solution to Mandel's problem with the most general matrix anisotropy is presented. This newly derived analytical solution for fully anisotropic materials has all the three nonzero shear strains. Warping occurs in the cross sections, and a generalized plane strain condition is fulfilled. This solution can be applied to transversely isotropic and orthotropic materials whose material symmetry axes are not aligned with the vertical loading direction. It is the first analytical poroelastic solution considering mechanical general anisotropy of elasticity. The solution captures the effects of material anisotropy and the deviation of the material symmetry axes from the vertical loading direction on the responses of pore pressure, stress, strain, and displacement. It can be used to match, calibrate, and simulate experimental results to estimate anisotropic poromechanical parameters. This generalized solution is capable of reproducing the existing solutions as special cases. As an application, the solution is used to study the responses of transversely isotropic and orthotropic materials whose symmetry axes are not aligned with the vertical loading direction. Examples on anisotropic shale rocks show that the effects of material anisotropy are significant. Mandel-Cryer's effects are highly impacted by the degree of material anisotropy and the deviation of the material symmetry axes from the vertical loading direction. 相似文献
8.
Mohammed Saiful Alam Siddiquee M. S. Islam F. Tatsuoka M. K. Islam 《Geotechnical and Geological Engineering》2018,36(3):1447-1462
Soil is a heterogeneous material and most natural soil deposits show a definite stratification. The mechanical behaviour of such material is generally different in different directions, especially in the direction parallel and perpendicular to the stratification. A series of isotropic compression tests were carried out to study the behavior of granular material produced under controlled stratification in the laboratory. These tests were conducted both on cylindrical and square prismatic tri-axial specimens. It was observed that for hydrostatic loading, the strain response was different in different directions, especially in directions parallel and perpendicular to the direction of soil deposition. A definite trend of anisotropy was observed in the deformation pattern. The observed anisotropy is modeled in this paper by treating soil-dilatancy as a variable quantity. The equation of the plastic potential surface of the model which obeys a non-associated flow rule, is assumed to be dependent on three main variables confining pressure (\(\sigma_{3}\)), void ratio (e) and the angle of bedding plane orientation (δ) during deposition. The angle of bedding plane orientation (δ) was measured with respect to the direction of the major principal stress. The model has a cap yield surface in the isotropic stress direction, which is supplemented by a shear hardening Mohr–Coulomb surface in the deviator direction. This paper focuses on predicting the anisotropic strain response of stratified soil deposits subjected to isotropic compression. The proposed anisotropic model incorporates within an existing strain-hardening sand model, a modified cap yield surface and a modified plastic potential function related to the cap surface, to account for the anistropic response observed in isotropic compression tests. The two dimensional stress–strain model was extended to three dimensional Cartesian space. The strain anisotropy observed in the isotropic compression tests was predicted by the three dimensional anisotropic model proposed for granular materials. 相似文献
9.
For technical reasons, virtually all plastic deformation experiments on geological materials have been performed in either pure shear or simple shear. These special case loading geometries are rather restrictive for those seeking insight into how microstructure evolves under the more general loading geometries that occur during natural deformation. Moreover, they are insufficient to establish how plastic flow properties might vary with the 3rd invariant of the deviatoric stress tensor (J3) which describes the stress configuration, and so applications that use those flow properties (e.g. glaciological and geodynamical modelling) may be correspondingly compromised. We describe an inexpensive and relatively straightforward modification to the widely used Paterson rock deformation apparatus that allows torsion experiments to be performed under simultaneously applied axial loads. We illustrate the performance of this modification with the results of combined stress experiments performed on Carrara marble and Solnhofen limestone at 500°–600 °C and confining pressures of 300 MPa. The flow stresses are best described by the Drucker yield function which includes J3-dependence. However, that J3-dependence is small. Hence for these initially approximately isotropic calcite rocks, flow stresses are adequately described by the J3-independent von Mises yield criterion that is widely used in deformation modelling. Loading geometry does, however, have a profound influence on the type and rate of development of crystallographic preferred orientation, and hence of mechanical anisotropy. The apparatus modification extends the range of loading geometries that can be used to investigate microstructural evolution, as well as providing greater scope for determining the shape of the yield surface in plastically anisotropic materials. 相似文献
10.
R. K. Dubey 《Journal of the Geological Society of India》2018,91(1):109-114
The deformation and mechanical responses of rocks are prime concern in development of varieties of civil and mining engineering structures. The deformation and mechanical properties of both natural and artificial materials are strongly depend on mineral constituents and their arrangements, temperatures and pressures, stress rates and structural anisotropy. This study elaborates an understanding of structural anisotropy, compression rates and mechanical attributes relationship in rocks with specific examples of deformed rocksalt. The cubical samples (5X5X5 cm3) with three kinds of structural anisotropy were subjected to quasistatic compressive stress at rates 0.00035 MPa/min, 0.0035 MPa/min, 0.035 MPa/min, 0.35 MPa/min, 3.5MPa/min, 5 MPa/ min, 7MPa/min and 9 MPa/min on servo-controlled Material Testing System (MTS). The stress-strain curves prepared from deformation of rocksalt’s samples under different rates of compressions are used to determine major mechanical parameters viz., strengths, strains, and modulus of elasticity. A micromechanical en-echelon crack array model is proposed to explain the influence of structural anisotropy on deformation patterns and mechanical properties of rocksalt.According to the proposed model the deformation progresses due to different proportional contributions of tensile and shear crack arrays under the influence of structural anisotropy. The control of structural anisotropy loses with respect to increment in rate of compression with enhance contribution of shear crack arrays in comparison to tensile crack arrays and ultimately fails in shear where the structurally anisotropic rock show isotropic behaviour. 相似文献
11.
为了研究板裂千枚岩的微观结构及力学性质,以汶川-马尔康高速公路沿线典型的板裂千枚岩为研究对象,进行了X衍射,薄片鉴定和单轴、三轴压缩试验。结果表明：1）板裂千枚岩微观结构和矿物成分比较复杂,具有明显的脆、塑性变形和裂隙,结构稳定性差;2）板裂千枚岩的各向异性明显,结构面夹角从0°到90°,板裂千枚岩的弹性模量、抗压强度、黏聚力和内摩擦角先减小后增大,呈V型分布规律;3）板裂千枚岩的破裂模式与结构面夹角和围压的大小密切相关,其破裂模式共有顺结构面的张拉劈裂破坏、顺结构面的剪切滑移破坏、Y型张拉-剪切复合破坏、顺结构面和贯穿结构面的复合张剪破坏、贯穿结构面的剪切破坏5种类型;4）随着围压的增大,不同结构面夹角试样的强度、变形参数和破裂模式的各向异性逐渐减弱;5）最大主应力与结构面的组合方式控制着岩石的破裂模式和力学性质,这是板裂板裂千枚岩显示各向异性的根本原因。 相似文献
12.
由于加荷方式不同,土体在复杂应力状态下在各主应力方向上应力-应变关系表现出显著应力各向异性,在常规三轴试验基础上,采用经典弹塑性理论各向同性土体模型对此不能合理描述。通过真三轴试验,总结应力各向异性柔度矩阵规律,结合试验规律进行相应理论研究,用非线性各向异性弹性矩阵代替弹塑性模型的弹性矩阵,用具有各向异性屈服准则的弹塑性模型描述塑性部分,建立非线性各向异性弹性-塑性模型,可以改善柔度矩阵矩阵形态,反映复杂应力状态下土体应力各向异性特征。 相似文献
13.
利用GDS应力路径三轴试验系统对南阳膨胀土进行3种应力速率下、4种超固结比（OCR）的被动压缩三轴试验及3种超固结比的被动挤伸三轴试验,分析了不同超固结比和应力速率下其应力（孔隙水压力）-应变关系、有效应力路径及变形模量的演化规律,对膨胀土变形模量各向异性特性进行了初步探讨。结果表明,应力速率、超固结比及卸荷路径均对膨胀土力学特性有一定影响。在被动压缩路径和被动挤伸路径下,随着应力速率和超固结比的增加,相同轴向应变时的偏应力值单调增加;不同超固结比和应力速率时膨胀土的孔隙水压力始终为负值,且其降幅总体上随超固结比的增加而增大,但其降幅随应力速率的变化规律与剪切路径有关。在被动压缩路径下,相同应变时不同应力速率下的孔压降幅基本相同;而在被动挤伸路径下,其降幅随应力速率的增加而增大。边坡开挖路径的选择对于边坡变形影响显著,被动挤伸路径下达到设定极限偏应力时的轴向应变明显大于被动压缩路径。膨胀土变形模量E100随着超固结比和应力速率的增加而增加,但各应力速率下变形模量的各向异性特性则随着超固结比的增加而变弱。 相似文献
14.
雪峰山隧道砂板岩各向异性力学特性的试验研究 总被引：4，自引：0，他引：4
利用MTS815 Flex GT岩石力学试验系统,对雪峰山隧道围岩中的砂板岩开展单轴和三轴试验,研究这种砂板岩中的细微层理对岩石变形特性、强度特性及其参数的影响,结果表明：岩石力学特性的各向异性特征显著。层理面与轴向力夹角0°时应力-应变曲线呈不稳定破裂特征,破坏面沿层理面方向发育;夹角90°时曲线呈峰后迅速软化特征,破坏面为对角贯通性剪切破坏。单轴试验中夹角0°的抗压强度比夹角90°高出约20%,弹性模量和变形模量比夹角90°分别约大50%和80%。三轴试验中2种夹角情况破坏时主应力差 相近,夹角0°的弹性模量和变形模量分别比夹角90°时约大6%和20%,围压对砂板岩的各向异性特征有弱化效应。这些结论揭示了该砂板岩各向异性的力学特性,对解决工程实际问题有重要的参考价值 相似文献
15.
针对黄土隧道开挖过程中不同部位（拱顶或拱腰）处围岩表现出的变形及强度各向异性情况,以宝鸡-兰州客运专线王家沟隧道原状黄土为例,着重探讨原状黄土结构强度各向异性问题。分别取王家沟隧道原状黄土水平与竖直方向进行抗剪、无侧限抗压及抗拉强度试验研究,考虑结构性对各向异性的影响,并对王家沟原状黄土进行电镜扫描,从微观结构上分析原状黄土具有各向异性的原因,最后探讨了原位状态下黄土各向异性的发生机制。结果表明：水平与竖直向应变比随围压的增大而减小,随归一化偏差应力的增大先增大后减小,峰值点随归一化偏差应力呈幂函数递增。提出原状黄土结构强度各向异性几何模型,并给出原状黄土各向异性强度参数指标。 相似文献
16.
A novel conceptual model of the mechanics of sands is developed within an elastic–plastic framework. Central to this model is the realization that volume changes in anisotropic granular materials occur as a result of two fundamentally different mechanisms. The first is purely kinematic, dilative, and is the result of the changes in anisotropic fabric. There is also a second volume change in granular media that occurs as a direct response to changes in stress as in a standard elastic/plastic continuum. The inclusion of the two sources of volume change results in three important datum states. When subjected to isotropic strains, the resulting stress state in granular materials is not isotropic but lies upon the kinematic normal consolidation line. There exists a state at which the fabric‐induced volumetric strain rate becomes equal to the stress‐induced volumetric strain rate making the total plastic volumetric strain rate equal to zero. Granular response changes from contractive to dilative at this phase transformation line. The third datum state is the one in which the stress‐induced volumetric strain rate is zero. The sand, however, continues to dilate at this state with the difference between stress and dilation ratio a constant as predicted by Taylor's stress–dilatancy rule. These predictions are shown in accordance with experimental data from a series of drained tests and undrained on Ottawa sand. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
17.
18.
大理岩弹塑性耦合特性试验研究 总被引：6，自引：0，他引：6
大量研究表明,岩石经历塑性变形时其弹性参数会发生变化,即存在弹塑性耦合现象。为了研究岩石的弹塑性耦合特性,进行了两种大理岩的循环加、卸载试验。试验结果表明:与常规试验对比,循环加、卸载试验对岩石的变形、强度及破坏形态影响较小;弹性参数随塑性变形的变化显著,考虑弹塑性耦合时,弹性参数取体积模量和剪切模量更为合适;基于Mohr-Coulomb屈服准则,计算得到了强度参数,即黏聚力和内摩擦角随塑性内变量的演化规律。所得结论将为岩石弹塑性耦合本构模型的建立提供基本的试验支持。 相似文献
19.
Pierre Bésuelle Gioacchino Viggiani Jacques Desrues Cécile Coll Pascal Charrier 《Rock Mechanics and Rock Engineering》2014,47(1):143-155
This paper reports some results of a large experimental program on Boom Clay conducted in Grenoble in the framework of the European project SELFRAC. The program included isotropic compression up to relatively high stress, drained triaxial compression tests at different cell pressures, as well as permeability measurements under isotropic and deviatoric stress. Local measurement of axial and radial displacements allowed the detection of strain localization during deviatoric loading. The permeability of Boom Clay is found to depend on the mean effective stress. The response of Boom Clay during deviatoric loading appears to be strongly affected by the swelling experienced during the isotropic stage preceding triaxial compression. The rate of swelling decreases with isotropic stress. The longer the swelling before shear, more the response under shear becomes ductile and the lower the initial stiffness. Permeability depends on the mean effective stress and it is found to decrease of about two orders of magnitude when the mean stress increases from 1 to 32 MPa. Permeability during shear loading is essentially constant and does not seem to be affected by strain localization. These results are complemented by a few observations obtained using X-ray microtomography in the framework of the more recent European project TIMODAZ. These findings illustrate the impact of pre-existing inclusions and fissures on specimen deformation upon deviatoric loading in the laboratory. 相似文献
20.
Microplane damage model for jointed rock masses 总被引：1，自引：0，他引：1
The paper presents a new microplane constitutive model for the inelastic behavior of jointed rock masses that takes into account the mechanical behavior and geometric characteristics of cracks and joints. The basic idea is that the microplane modeling of rock masses under general triaxial loading, including compression, requires the isotropic rock matrix and the joints to be considered as two distinct phases coupled in parallel. A joint continuity factor is defined as a microplane damage variable to represent the stress‐carrying area fraction of the joint phase. Based on the assumption of parallel coupling between the rock joint and the rock matrix, the overall mechanical behavior of the rock is characterized by microplane constitutive laws for the rock matrix and for the rock joints, along with an evolution law for the microplane joint continuity factor. The inelastic response of the rock matrix and the rock joints is controlled on the microplane level by the stress–strain boundaries. Based on the arguments enunciated in developing the new microplane model M7 for concrete, the previously used volumetric–deviatoric splits of the elastic strains and of the tensile boundary are avoided. The boundaries are tensile normal, compressive normal, and shear. The numerical simulations demonstrate satisfactory fits of published triaxial test data on sandstone and on jointed plaster mortar, including quintessential features such as the strain softening and dilatancy under low confining pressure, as well as the brittle–ductile transition under higher confining pressure, and the decrease of jointed rock strength and Young's modulus with an increasing dip angle of the joint. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献