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单粒组密砂剪切带的直剪试验离散元数值分析 总被引：7，自引：1，他引：6
为分析砂土的剪切力学特性,采用离散元商业软件PFC2D对单粒组密砂在直剪试验中出现的剪切带进行了数值分析。改进传统的分条带观察方式,采用矩形格分割法观察试样内部不同区域的变形特性。对离散元商业软件进行了二次开发,实现了大小主应力及其应力主方向角的可视化,分析了试样内部的应力偏转情况。同时,以纯转动率和颗粒速度等微观变量为中心,观察了试样内部颗粒的运动状态,解析了直剪试验中砂土剪切带形成的微观机制。研究表明,直剪试验中应变局部化区域集中在剪切面附近的一个条带内。通过转动场和速度场的分析可知,剪切带宽度约为10～15倍的砂土平均粒径,带内颗粒转动明显,带边缘出现大的速度和转动变化梯度。对组构和接触力分布的分析可知,剪切过程中粒间接触点和接触力的主轴方向发生了相一致的偏转,偏转后的主轴方向为60°左右。 相似文献
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在平面应变压缩条件下,采用拉格朗日元法研究了材料缺陷对岩样应变局部化及宏观力学行为的影响。在数值计算中,采用了莫尔-库仑与拉破坏复合的破坏准则,峰后岩石的本构关系为线性应变软化。对于理想岩样（不含任何缺陷）,从剪切应变率的等值线图及变形网格图发现,变形场相对试样垂直对称轴对称。在试样的边界上设置材料缺陷后,变形场的对称性被打破。材料缺陷附近是局部化现象启动的主要位置。与不含材料缺陷试样相比,含缺陷试样的局部化提前启动。当缺陷位于试样左边界中部附近时,试样内部出现多条剪切带,发生韧性剪切破坏,峰后应力-轴向应变曲线和应力-侧向应变曲线均倾向于韧性,岩样的稳定性增强;当缺陷位于试样上、下端面附近时,仅出现一条贯穿试样左右边界的剪切带,发生脆性剪切破坏,峰后两种曲线倾向于脆性,易发生失稳破坏。从数值结果中还观测到了剪切带的跳跃或迁移现象及剪切带的相互竞争、此消彼涨的现象。当岩样中不包含任何缺陷时,试样应力-变形曲线的峰值强度最高。随着缺陷的上移,峰值强度下降,直到峰值强度基本保持不变。缺陷越接近于岩样的下端,对岩样应力-变形曲线的峰值强度的影响越小。 相似文献
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《岩土力学》2016,(1):229-236
通过引入考虑范德华力和抗转动作用的月壤微观接触模型,采用离散单元法模拟月壤水平推剪试验(简化的土-开挖设备间相互作用模型),对月壤推剪破坏机制进行研究,分析了推剪深度、倾角和速率的影响,为真实月面环境下开挖提供参考。结果表明:推剪过程中推剪阻力首先随推剪位移增加至峰值,而后下降并趋于稳定;随推剪位移的进一步发展,推墙前方土体堆积,推剪阻力缓慢回升,推墙前土体受扰动区范围逐渐增大;当推剪面竖直时,随着推剪深度增加,推剪阻力和能量消耗增大,前方受扰动土体范围增大,破坏面为直平面;相同推剪深度下,推剪倾角越大,推剪阻力和能量消耗越小,前方扰动土体范围越小,破坏面为直平面;推剪速率越大,推剪阻力和能量消耗增大,前方扰动土体范围越大。由于月面开挖时推剪反力由机械与月面摩擦提供,考虑到开挖机械重量受空间运输能力限制,建议采用对推力(机械重量)要求低的浅层、倾斜、慢速开挖,适用于月面早期建设活动。 相似文献
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基于亚像素角点检测的数字图像测量系统能够记录三轴试样表面方块角点的位移,从而获得试样表面每一时刻的局部应变及应变场。分析了试样不同位置的局部径向应变在剪切过程中的变化,获得了以不同初始成样含水率制备的松砂和密砂试样在不同特征时刻的应力与应变的特征值。通过轴向应变场的变化分析了从应变局部化出现到剪切带发育、形成的这一完整的渐进破坏过程,总结了剪切带形成时的局部最大轴向应变特征值,并定性地分析了剪切带内、外土体在渐进破坏过程中不同的轴向应变增长率。试验结果表明：在应变场中试样应变局部化明显,并可以依此确定应变局部化的出现、剪切带的形成;对于密砂及初始含水率为0%制备的松砂试样,应力在应变局部化出现之初即达到峰值,剪切带形成时应力已经开始下降,进入应变软化阶段;以初始含水率为6%和12%制备的松砂试样在达到应力峰值时剪切带已经形成;剪切带内土体的局部轴向应变增长幅度比剪切带外的土体大得多。试样整体轴向应变的增大主要是由剪切带内土体剪切破坏产生的较大轴向应变所致。 相似文献
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利用自主开发的基于无网格法的岩石力学计算分析程序,采用Mohr-Coulomb破坏准则,考虑材料塑性屈服后的软化特性,研究单轴压缩条件下含一个缺陷的岩石试样的变形特性,探讨含缺陷材料的岩石变形局部化的演化规律。计算结果表明,岩石试件的破坏是一个渐进破坏的过程;加载过程中试件中的缺陷弱粒子首先出现粒子破坏并产生声发射,随加载进行试件产生微裂隙并扩张形成一个变形局部化带,局部化带扩张、发展,最终形成一个明显的剪切破坏带,缺陷粒子对试件的破坏起到了控制作用。岩石的声发射记录了岩石材料的塑性破坏过程,岩石试件的剪切破坏带与塑性区的发展具有非常类似的规律,但塑性区面积要大于剪切破坏带,从所处位置来看剪切破坏带位于塑性区之内,通过研究声发射特征信息发现变形局部化发生在应力-加载步（应变）达到峰值强度前。 相似文献
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应变软化扩容对含随机缺陷岩石的渐进变形及破坏前兆特征的影响 总被引：3，自引：3，他引：0
在单轴平面应变压缩条件下, 采用FLAC模拟了剪切扩容对含随机缺陷岩石破坏前兆及变形特征的影响。密实的岩石服从莫尔库仑剪破坏与拉破坏复合的破坏准则, 破坏之后呈现应变软化-理想塑性行为。缺陷在破坏之后经历理想塑性行为。随着轴向应变的增加, 试样内部破坏的单元数目增加, 直到达到一个常数, 该常数随着扩容角的增加而增加。当扩容角较高时, 计算得到的泊松比在峰前就可以超过0.5;剪切扩容于峰前发生; 变形后试样的最终体积大于初始体积。剪切局部化(导致了毗邻块体之间的相对滑动)及剪切扩容(发生于剪切带内部)是非零扩容角试样峰后体积膨胀的原因。在峰前, 通过观察剪切应变增量、破坏的单元数目、侧向应变、计算得到的泊松比及体积应变可以发现, 扩容角越高, 试样破坏的前兆越明显。在低扩容角时, 由于弯曲的剪切带边界, 试样内部充分发展的剪切带的倾角比较分散, 剪切带的倾角更接近Arthur理论。 相似文献
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模拟月壤地面力学性质试验研究 总被引：4，自引：0，他引：4
掌握与月球车行驶相关的月壤力学性质是我国月球车研制所急需的。在制备了用于月面车辆力学试验用的模拟月壤基础上,通过三轴试验得出模拟月壤的弹性模量为48.8 MPa;通过硬度测量可知,模拟月壤的硬度小于黑壤土,与石英砂接近;通过压板试验可得模拟月壤的变形指数n为1.13,变形模量K为1 056 kN/mn+2,分析可知,随着变形模量和变形指数的增大,其承压能力增大;通过履带板试验可得模拟月壤剪切变形模量k为1.2 cm,分析可知,剪切破坏模量的增大对剪切强度的影响不大,但会使剪切破坏的峰值向后移动;另外,随着内摩擦角? 和黏聚力c的增加,剪切破坏强度增大。以上研究结果可为月球车行走机构优化设计和通过性能评估提供参考和依据。 相似文献
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月面环境与月壤特性研究的主要问题探讨 总被引：6，自引：0，他引：6
月面环境与月壤特性是月球探测和月球科学研究的重要基础,对它们的研究一直在不断加深,本文对月球表面地形地貌、热环境以及月壤特性三个方面的研究现状进行了总结,初步分析了这三个方面研究目前存在的一些主要问题：（1）地形地貌对月球定量遥感的影响以及南极艾特肯（SPA）盆地等地貌单元的年代学划分和成因演化;（2）月面热辐射、月表物理温度和热流等月面热环境特征的进一步探测和全面分析,以及其对地球反照率变化的响应;（3）月壤形成演化过程及空间风化作用,月球极区氢富集机制和水冰探测,以及月球资源开发利用。 相似文献
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用于月面车辆力学试验的模拟月壤研究 总被引：9，自引：1，他引：8
研究月面环境下的车辆地面力学,对保证月球探测车辆的正常工作具有重要意义,而用于月面车辆力学试验的模拟月壤则影响其结果的准确度与可信度。用于月面车辆力学试验的模拟月壤,以月壤样本与JSC-1模拟月壤为参考标准,以吉林辉南县火山灰为主要原料、赤铁矿砂为辅料,通过调整试样的粒径分布与赤铁矿砂含量,使模拟月壤的比重、内摩擦角、凝聚力、承压特性、粒径分布、颗粒形态、矿物组成等参数接近JSC-1模拟月壤,并在月壤样本的参数变化范围之内,表明该模拟月壤可用于月面车辆力学试验研究。 相似文献
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《Geomechanics and Geoengineering》2013,8(4):235-251
The bearing capacity of footing has been studied by both conventional and numerical methods by many researchers. However, degradation of the microstructure of material, that is, a change in the microstructure of the soil, has not been adequately taken into account. Degradation of microstructure causes strain softening of materials and it leads to strain localization such as shear bands and slip bands. From an engineering point of view the strain localization is crucial because it is a precursor of failure. In the present study, finite element analyses of the bearing capacity of a shallow foundation on homogeneous and inhomogeneous saturated clay strata have been conducted using an elasto-viscoplastic soil constitutive model of microstructure change. A series of analyses of footing on clay deposit with different microstructure parameters have been carried out. Numerical results show that strain localization can be predicted during the loading of rigid footing on highly structured soil and strain localization affects the footing–soil interaction. The effects of footing roughness on the failure mechanism are also discussed in the study. 相似文献
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Modelling shear band is an important problem in analysing failure of earth structures in soil mechanics. Shear banding is the result of localization of deformation in soil masses. Most finite element schemes are unable to model discrete shear band formation and propagation due to the difficulties in modelling strain and displacement discontinuities. In this paper, a framework to generate shear band elements automatically and continuously is developed. The propagating shear band is modelled using discrete shear band elements by splitting the original finite element mesh. The location or orientation of the shear band is not predetermined in the original finite element mesh. Based on the elasto‐perfect plasticity with an associated flow rule, empirical bifurcation and location criteria are proposed which make band propagation as realistic as possible. Using the Mohr–Coulomb material model, various results from numerical simulations of biaxial tests and passive earth pressure problems have shown that the proposed framework is able to display actual patterns of shear banding in geomaterials. In the numerical examples, the occurrence of multiple shear bands in biaxial test and in the passive earth pressure problem is confirmed by field and laboratory observations. The effects of mesh density and mesh alignment on the shear band patterns and limit loads are also investigated. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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基于破损力学理论,将结构性黄土抽象成具有一定结构强度的结构块和摩擦带组成的二元介质模型。对结构性黄土体来说,局部化剪切带问题也是土体的破损问题,剪切带萌生发展的实质就是结构块向摩擦带转化的动态过程。应用结构性土的双参数破损率二元介质本构模型,采用数值分析方法模拟了平面应变压缩条件下结构性土中局部化剪切带萌生、扩展的过程,研究了不同缺陷方案下局部化剪切带的形态、特性与规律,发现结构性土中局部化剪切带的发展起初是由一段段不连续的微小局部破坏区域在外荷载逐步作用下渐进扩展连接贯通而形成整体剪切带的破坏形式。二元介质本构模型和常规有限元的结合,形象生动地再现了局部化剪切带萌生、发展的过程。 相似文献
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Use of acoustic emissions to investigate localization in high-porosity sandstone subjected to true triaxial stresses 总被引：4，自引：3，他引：1
Acoustic emissions were used to investigate the evolution of damage and strain localization in Castlegate sandstone specimens subjected to true triaxial states of stress, where the intermediate principal stress ranged from equal to minimum compression to equal to maximum compression. Three failure modes were observed: shear band formation at low mean stresses, compaction localization at intermediate stresses, and no localization at high mean stresses. For shear bands, the onset of localization consistently occurred prior to peak stress, while compaction localization initiated at the beginning of a stress plateau. The band angle (defined as the angle between the band normal and the maximum compression direction) determined by fitting a plane through the localized acoustic emission events corresponded well with the shear band angle expressed on the specimen jacket. As expected, the band angle decreased with increasing mean stress. The theoretically predicted dependence of band angle on deviatoric stress state was not confirmed; however, data scatter due to natural variations in material could obscure such a trend. Each failure mode displayed a unique acoustic emission rate response; therefore, this rate response alone can be used to determine the failure mode and the onset of localization in Castlegate sandstone. 相似文献
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巫山加筋土的三轴试验研究 总被引：1，自引：0，他引：1
用常规三轴仪，研究了巫山县集仙中路1号加筋土挡墙加筋填土在不固结、不排水条件下的变形破坏机理和抗剪强度性质。试验结果表明，该加筋填土的抗剪强度性质虽较不加筋土有一定提高，但由于筋带表面网格细微，与土体之间的咬合摩擦力较弱，易在筋带与土体之间产生人为的滑动面，从而造成加筋土抵抗小，变形的能力减低；同时试验还表明，加筋层数和围压也是决定加筋土性质的重要因素。 相似文献
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For evaluation of slope stability in materials displaying strain-softening behavior, knowledge concerning the failed state material response is of importance. Here, soft sensitive clay is studied. Such clays behave contractant at failure, which for undrained conditions yields a strain-softening behavior governed by the generation of excess pore water pressure. Strain softening is further linked with material instability and the phenomenon of strain localization. In the case of shear band formation, internal pore pressure gradients are then expected to be present for globally undrained conditions in the sensitive clay due to its low permeability. In the present study, this hypothesis and its implications on the global response and shear band properties are investigated. Utilizing an experimental setup with a modified triaxial cell allowing for shear band formation, the effect of varying the displacement rate is studied. Onset of strain localization is interpreted to occur just before or at the peak shear strength. A strong rate dependency of the softening response is observed. Increasing displacement rates give raised brittleness in terms of the slope of the global softening curve due to accumulating pore pressure. Also, reduced shear band thickness and a shear band inclination approaching 45° are obtained for increasing rates. In the context of slope failure in such materials, the rate dependency in the post-peak state opens up for a large variation in behavior, all depending on time as an important factor. 相似文献
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The appearance of shear banding in granular materials has been investigated intensively during the last decades and is still of ongoing importance in terms of understanding the stress–strain behaviour of the material, the localization phenomena and the interaction between soil and structure. Only less attention has been paid to the occurrence of systems of shear bands although such systems can be identified in geotechnical structures as well as in geological formations. In this paper we present results of experiments on sand specimens under extensional load in natural gravity as well as in increased gravity in the centrifuge where the influence of the stress level on the geometry of a shear band pattern, specified by the spacing of the shear bands and the angle between failure surfaces and minor stress direction, has been investigated. X‐ray technique has been used to visualize the failure zones inside the specimen, an optical measurement system called Digital Image Correlation has been applied to identify and observe the appearing deformation mechanism on the sides of the specimens in natural gravity as well as during the flight in the centrifuge. It can be shown that the geometry of the shear band pattern is sparsely influenced by the change of the stress level. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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作为行星地质学与行星工程学的交叉学科,行星地质工程学科直接支撑行星探测、行星科研站与基地建设、行星资源开发与未来人类移居,相关研究已迫在眉睫。与地球相比,行星地质体在物质、结构与环境3个方面存在较大差异,决定着行星地质体工程特性与地球具有很大的差别,开展行星地质工程原位测试是准确获取行星地质体工程特性的最直接方式。文章把月球探测和火星探测任务中地质工程原位测试方法分为5类:触探试验、铲斗试验、钻探试验、地球物理探测和摄影测量,分别分析了各类原位测试方法的原理与科学载荷,对比各种方法中不同测试仪器的差异;利用月球工程特性原位测试结果梳理总结了月壤工程特性,包括粒度分布、密度、孔隙比、抗剪性、压缩性和承载力,分析了月壤和火壤工程特性的变化规律,并指出了与地球土壤物理力学特性的差异;未来应以行星探测任务为载体,结合地面低重力模拟测试平台和物理力学本构理论研究,研制小型轻量、自动智能的工程特性原位测试科学载荷,获取更加准确的行星土壤和岩石的工程特性参数,支撑月球科研站、基地建设和火星取样返回等深空探测任务。 相似文献