土体塑性各向异性的微宏观机理分析

基于微观土力学理论框架推导了宏观应力解析,将各向异性的微观机理归结为微观接触力各向异性和微观组构各向异性的两方面因素。应用基于微观理论的应力解析构建了土体各向异性强度准则,并结合既有的微、宏观试验及理论成果,研究加载条件对硬化定律的影响机理,进而揭示了变形非共轴性的微观理论基础。研究表明,着眼于微观理论机理,强度各向异性和塑性变形各向异性本质上都是微观组构各向异性的宏观表现。其中,强度各向异性起源于土体微观组构的固有各向异性,而塑性诱发各向异性依赖于塑性硬化过程中微观组构各向异性的演化规律。在比例加载条件下土体表现为等向硬化和共轴塑性,而非比例加载条件下表现为等向-运动硬化和塑性非共轴性     

各向异性花岗岩的强度和变形机制实验研究

<正>1研究背景在岩石流变实验研究中,大多数实验采用各向同性的均匀样品,其实验结果与地壳伸展和拆离断层形成相关的各向异性岩石的流变特征有很大差别。组构对片岩、片麻岩变形影响的实验研究结果表明,先存变形组构对岩石脆性破裂、半脆性流变的强度具有显著影响,对新组构的发育和形成具有明显控制作用,但大部分实验仅给出各向异性岩石强度,缺少流变参数和变形机制研究,对复杂组构岩石的塑性流变行为也不清楚。中地壳流变状态对地壳拆离断层的形成具有制约作用。开展具有先存组构岩石的流变实验,能     

高温高围压下岩石压缩组构与各向异性

一、引言岩石组构可分为三种:由沉积和岩浆流动造成的原生组构;岩体变形时,间隙溶液沿易于运动的方向生长成晶体,或裂隙溶液受两壁控制结晶而成的附生组构;岩石形成后,受构造应力作用而成的后生组构。它们都是造成岩石力学性质各向异性的重要原因。岩石中造岩矿物晶粒的规则排列程度愈强,岩石力学性质的各向异性愈显著,由于岩石后生组构是在岩体一定方式的变形中形成的,因而也是鉴定构造应力场和构造运动序次的重要方法,尤其是当构造已被剥蚀难以从形象上鉴定时,更有其独特作用。岩石力学性质的各向异性,直接影响岩体强度、波速和应力的空间分布,并使得这种     

低温变形与低温成矿作用讨论——以贵州某些汞、金矿床为例

低温变形是变形岩石清楚地保持原岩组构的非均匀变形。在低温变形的岩石中,可见物质的旋转、破裂、压溶及颗粒规模的晶体塑性。这种变形主要反映穿粒(Transgranu-lar)机制。在低温变形中晶体塑性变形的特征主要表现有:双晶片(这Twin Lamellae)、变形带(Deformation bands)和波状消光等。Groshong(1988)指出,在低温变形中,晶体塑性应变的上限是20%[1]。低温变形实际是一种脆性或半脆性变形。他(1981)测定     

考虑初始损伤和蠕变损伤的岩石蠕变全过程本构模型

考虑到天然岩石存在不同程度初始损伤以及蠕变过程中岩石受载后裂隙扩展而导致的新损伤,对具有初始损伤的岩石蠕变特性进行全面描述。根据不闭合结构面应力与法向变形之间的关系,提出裂隙岩石塑性变形体元件,描述岩石蠕变过程中的瞬时塑性变形。引入初始损伤影响因子,建立具有初始损伤的岩石损伤变量演化方程,构建模拟岩石加速蠕变的蠕变损伤体元件。将裂隙岩石塑性变形体和蠕变损伤体与描述瞬时弹性变形和黏弹性变形的广义开尔文模型进行串联组合,形成能够反映具有初始损伤的岩石瞬时弹-塑性变形、稳定蠕变和加速蠕变的蠕变全过程本构模型,提出了进行少量蠕变试验既能解析模型参数的方法,在不同应力水平下模型理论曲线与蠕变试验曲线吻合。     

不同温压下岩石弹性波速度、衰减及各向异性与组构的关系

结合岩石组构分析 ,阐述了岩石弹性波传播速度和衰减以及它们的各向异性与岩石组构之间的关系。在不同温压条件下对具有很强晶格优选方位的岩石样品的研究表明 ,随着围压的增加 ,波速和Q值均增大 ,但是在相互正交的 3个方向上 (垂直或平行于层理面及线理方向 )增大的速度并不相同 ,这与微裂隙的逐渐闭合密切相关。观测到的波速和Q值的各向异性具有不同的形成机理 ,波速各向异性主要与定向分布的微裂隙和主要矿物的晶格优选方位等构造因素有关 ;高围压下Q值各向异性与速度各向异性正好相反 ,可能是由于定向排列的矿物晶体沿不同方向其边界之间接触程度不同造成的。对岩石组构的研究不仅可以揭示岩体的变形机制、变形的动力学过程及其有关的热力学信息 ,还可以对宏观岩石的各种物理性质 ,尤其是力学特性 ,从微观机理上加以解释。文中特别强调了岩石组构分析对研究岩石物理性质的各向异性具有十分重要的意义。     

基于微观力学机制的各向异性结构性砂土的本构模型研究

在岩土破损力学基础上,基于微观破损机制,提出了考虑各向异性的结构性砂土本构理论。采用Lade-Duncan强度准则考虑中主应力对抗剪强度的影响;采用考虑颗粒排列组构的各向异性状态变量A反映各向异性对土体强度和变形的影响;通过相似扩大重塑土的屈服面反映结构性对土性的影响;通过引入非相关联流动法则考虑各向异性和结构性对土体塑性变形的影响。同时,将基于微观力学机制的损伤演化规律引入结构性土的硬化规律;该硬化规律同时考虑了塑性体积应变和剪切应变对各向异性结构性土强度的影响。然后将该模型用于模拟室内三轴压缩试验,初步验证了该模型的合理性和适用性。     

北大别穹隆变形组构一期或多期形成:来自韧性变形组构叠加数值模拟的证据

矿物拉伸线理和面理是研究岩石韧性变形运动学的基本要素。然而自然界许多应变带内拉伸线理和面理产状分布往往并不单一。如何正确认识这类变形组构,并利用这些组构开展构造变形分析至今仍备受争议。本文基于Eshelby理论,通过数值模拟,研究了岩石经历两期不同韧性变形后面理和拉伸线理的产状特征。模拟结果显示岩石经历两期构造变形时,岩石中的较软矿物仅能保留下最后一期构造变形运动学信息。这一认识得到了北大别穹隆内变形组构的支持。北大别穹隆内产状复杂的拉伸线理只记录了造山后伸展期变形。本次数值模拟结果对野外构造观察和分析以及确定构造变形时间具有指导意义。     

从单晶褶皱看斜方辉石流变学的特征

迄今为止,上地幔流变学的研究主要集中于橄榄石单晶与多晶集合体的实验和野外观察,但对辉石的流变学特征知之甚少,虽然辉石亦是上地幔岩石的主要组成矿物.因此,查清斜方辉石的流变学行为、塑性变形机制、重结晶作用以及与其共生的橄榄石之间的流变强度差等,现已成为国际地学界研究的新的热点课题.新疆中天山南缘库米什地区的榆树沟高压变质地体中出现地幔超糜棱岩,其中带状拉伸的斜方辉石(En90)碎斑晶发生了强烈地弯滑褶皱,周围橄榄石(Fo90)重结晶成细粒(～10 μm)多晶基质.显微构造研究表明,单晶斜方辉石的褶皱主要通过单一的(100)[001]滑移进行的,而细粒重结晶橄榄石基质的变形机制则最可能以超塑性(颗粒边界滑移与扩散)为主.单晶斜方辉石发生弯滑褶皱,而不形成常见的膝折(Kinks),说明所处物理化学条件下斜方辉石晶体位错攀移与原子扩散并不足够活跃.此外,即使其晶格发生高达140.的旋转,斜方辉石依然没有发生光学显微镜下足以识别的重结晶结构,说明启动重结晶作用的临界剪切应变应不少于5.5.根据现有的层状材料的褶皱理论,推测榆树沟高压变质地体中地幔岩发生塑性变形时位错蠕变的斜方辉石的流动强度至少比相同条件下超塑性变形的细粒橄榄石多晶基质高近2个数量级.     

磁化率各向异性与剪切带

岩石组构记录了地壳形成与演化的关键信息,提取这些信息对分析和恢复地球动力学过程具有重要意义。磁化率各向异性(AMS)是一种重要的岩石组构方法,可以有效地揭示岩石的应变特征,分析其地球动力学过程,是研究构造变形性质以及应力作用方式的有效手段。本文在梳理AMS的研究历史、主要成果和最新进展的基础上,系统阐述了AMS的基本原理以及在剪切带的应用:①岩石组构具有复杂性,AMS作为一种间接组构手段受控于矿物的物理特性、含量以及变形变质等多方面因素;②AMS可以提供剪切带的运动学以及不同部位应变状态的信息;③对于剪切带,AMS主要受控于磁性矿物(矿物成分和粒度的变化导致全岩磁化率各向异性的变化)、构造变形强度(决定磁线理发展的重要因素)以及流体的作用(流体导致磁性矿物的类型与定向性的变化)。     

Heterogeneous deformation and texture development in halite polycrystals: comparison of different modeling approaches and experimental data

Modeling the plastic deformation and texture evolution in halite is challenging due to its high plastic anisotropy at the single crystal level and to the influence this exerts on the heterogeneity of deformation over halite polycrystals. Three different assumptions for averaging the single crystal responses over the polycrystal were used: a Taylor hypothesis, a self-consistent viscoplastic model, and a finite element methodology. The three modeling approaches employ the same single crystal relations, but construct the polycrystal response differently. The results are compared with experimental data for extension at two temperatures: 20 and 100 °C. These comparisons provide new insights of how the interplay of compatibility and local equilibrium affects the overall plastic behavior and the texture development in highly anisotropic polycrystalline materials. Neither formulation is able to completely simulate the texture development of halite polycrystals while, at the same time, giving sound predictions of microstructural evolution. Results obtained using the finite element methodology are promising, although they point to the need for greater resolution of the individual crystals to capture the full impact of deformation heterogeneities.     

Orientation Distribution Within a Single Hematite Crystal

While crystallography conventionally presumes that a single crystal carries a unique crystallographic orientation, modern experimental techniques reveal that a single crystal may exhibit an orientation distribution. However, this distribution is largely concentrated; it is extremely concentrated when compared with orientation distributions of polycrystalline specimen. A case study of a deformation experiment with a single hematite crystal is presented, where the experimental deformation induced twining, which in turn changed a largely concentrated unimodal “parent” orientation distribution into a multimodal orientation distribution with a major mode resembling the parent mode and three minor modes corresponding to the progressive twining. The free and open source software MTEX for texture analysis was used to compute and visualize orientations density functions from both integral orientation measurements, i.e. neutron diffraction pole intensity data, and individual orientation measurements, i.e. electron back scatter diffraction data. Thus it is exemplified that MTEX is capable of analysing orientation data from largely concentrated orientation distributions.     

Plagioclase preferred orientation by TOF neutron diffraction and SEM-EBSD

The lattice preferred orientation (LPO) of an anorthosite (composed of andesine) sampled from a highly deformed anorthositic mylonite (Grenville Province, Quebec) was measured by TOF neutron diffraction and SEM-EBSD. The quantitative texture analysis of neutron data was accomplished by using the Rietveld texture analysis with the WIMV algorithm, implemented in the program package Materials Analysis Using Diffraction (MAUD). The texture calculations of the EBSD data were performed by using the program BEARTEX. Analyses from neutron and electron diffraction data gave similar results if EBSD data are smoothed to account for grain statistics. The principal pole figures show (010) roughly parallel to the rock foliation, (001) poles exhibiting a low angle (25°) to the pole to foliation, and (100) poles close to the Y-direction (perpendicular to the lineation and foliation pole). The [100] crystallographic direction shows a maximum in the lineation direction, [010] directions concentrate near the foliation pole. The geological deformation conditions and the constructed pole figure patterns indicate that the preferred orientation could be attributed to intracrystalline slip dominantly on (010) with [100] as slip direction. Elastic properties, calculated by averaging, document weak anisotropy that has implications for the seismic structure of the lower crust.     

Texture development of polycrystalline anhydrite experimentally deformed in torsion

A polycrystalline aggregate of anhydrite was deformed in torsion to a maximum shear strain of 8.1 at 700°C and a maximum shear strain rate of 5᎒^-3 s^-1. The crystallographic preferred orientation (CPO or texture) was investigated as a function of shear strain/shear strain rate in a radial profile from the centre to the edge of the sample. A deformation texture developed at shear strains of 1.5-2 (corresponding to shear strain rates of 1 to 1.3᎒^-3 s^-1) and reached a stable position relative to the kinematic frame at a shear strain of 3.7 (2.3᎒^-3 s^-1). Further shear strain only led to a small increase in texture strength but no change in the orientation relative to the kinematic frame. The CPO is very similar to naturally observed textures and can be explained by the activity of the {001}<010> and {012}<121> slip systems. Although independent mechanical data indicate that a change of mechanism from dislocation- to diffusion-controlled creep occurred at a shear strain of approximately 1.5, the texture does not weaken, but rather increases, in strength with higher shear strains.     

Exploring the relative contribution of mineralogy and CPO to the seismic velocity anisotropy of evaporites

We present the influence of mineralogy and microstructure on the seismic velocity anisotropy of evaporites. Bulk elastic properties and seismic velocities are calculated for a suite of 20 natural evaporite samples, which consist mainly of halite, anhydrite, and gypsum. They exhibit strong fabrics as a result of tectonic and diagenetic processes. Sample mineralogy and crystallographic preferred orientation (CPO) were obtained with the electron backscatter diffraction (EBSD) technique and the data used for seismic velocity calculations. Bulk seismic properties for polymineralic evaporites were evaluated with a rock recipe approach. Ultrasonic velocity measurements were also taken on cube shaped samples to assess the contribution of grain-scale shape preferred orientation (SPO) to the total seismic anisotropy. The sample results suggest that CPO is responsible for a significant fraction of the bulk seismic properties, in agreement with observations from previous studies. Results from the rock recipe indicate that increasing modal proportion of anhydrite grains can lead to a greater seismic anisotropy of a halite-dominated rock. Conversely, it can lead to a smaller seismic anisotropy degree of a gypsum-dominated rock until an estimated threshold proportion after which anisotropy increases again. The difference between the predicted anisotropy due to CPO and the anisotropy measured with ultrasonic velocities is attributed to the SPO and grain boundary effects in these evaporites.     

基于细观变形理论的盐岩塑性本构模型研究

唯象学本构模型不能很好解决诸如夹杂含量、温度、应变速率等对盐岩力学性质的影响,更难以解释盐岩变形机制。盐岩为石岩晶体组成,其变形机制主要由多晶结构所控制,故基于固体位错理论研究方法建立的盐岩塑性本构模型更能反映盐岩的变形机制。研究表明,盐岩的塑性-蠕变交互作用机制是（亚）晶粒内部位错的滑移与（亚）晶界及其干涉面内位错的攀移运动之间的耦合。基于此,可确定亚晶（或晶粒）平均尺寸与流动应力之间的关系、（亚）晶内的位错平均密度;建立微观参量（位错、亚晶直径、亚晶界宽度等）演化模式;根据Orowan定律建立盐岩微观-宏观变形联系,从而导出盐岩塑性本构方程。导出的本构方程体现了盐岩塑性-蠕变变形的物理机制,相对于传统的塑性本构方程具有更好的物理意义。     

胶东黄铁矿显微构造变形与金富集关系：黄铁矿EBSD组构和地球化学约束

载金黄铁矿显微构造变形与金富集关系可以从显微-超显微尺度揭示金成矿作用和地质过程,探讨金的再活化或再聚集作用。在胶东焦家金矿带成矿期识别出4种类型的黄铁矿,文章应用光学显微镜、扫描电镜(SEM)、透射电镜(TEM)、电子背散射衍射(EBSD)和电子探针(EMPA)等技术方法,探讨黄铁矿显微构造特征、超微观结构与金的富集关系。结果显示:载金黄铁矿均不发育环带,其中w(Fe)为45.70%～46.85%,w(S)为52.57%～53.37%;显微构造变形既有脆性变形又有塑性变形;黄铁矿晶体优选方位(CPO)主要表现为平行于晶轴极密和复杂极密;黄铁矿晶格间距为0.58 nm,主要发育刃位错。焦家金矿带在金成矿作用过程中,可见金集合体经历了从复杂的纳米尺度到宏观尺度矿物载体富集的过程,包括成矿流体中金络合物、金-铋-硫族化合物富集等化学结构变化过程和纳米金、载金黄铁矿纳米颗粒、岩矿石显微-超显微构造微环境变化过程。因此,不同类型载金黄铁矿CPO受到化学结构变化和显微-超显微变形微环境变化的联合制约,间接反映出载金黄铁矿中金的富集与黄铁矿内部变形、表面形貌和结构缺陷有密切关系。     

Experimental and texture-derived P-wave anisotropy of principal rocks from the TRANSALP traverse: An aid for the interpretation of seismic field data

A representative suite of deformed, metamorphic rocks from the TRANSALP reflection seismic traverse in the Eastern Alps was studied in the laboratory with respect to elastic properties and whole-rock texture. Compressional wave (P-wave) velocities and their anisotropies were measured at various experimental conditions (dry, wet, confining pressure), and compared to the texture-related component of anisotropy. Here ‘texture’ refers to crystallographic preferred orientations (CPOs), which were determined by neutron texture goniometry. In gneisses and schists P-wave anisotropies are mainly controlled by the microcrack fabric. In marbles and amphibolites CPO contributes very significantly to anisotropy. At 200 MPa confining pressure the degree of anisotropy is between 5% and 15%, depending on rock composition and/or CPO intensity. Special emphasis was also put on discussing possible effects of fluids on seismic velocity and anisotropy. Distributions of water-filled microcracks and pores are distinctly anisotropic, with maximum contribution to bulk rock velocity mostly parallel to the foliation pole. Decreasing P-wave velocity and increasing anisotropy of immersed samples may be explained by crack-induced changes of the elastic moduli of bulk rock. The main conclusion regarding interpretation of TRANSALP data is that strong reflections in the deep Alpine crust are probably due to marble–gneiss and metabasite–gneiss contacts, although P-wave anisotropy and boundaries between zones of ‘dry’ or ‘wet’ series may contribute to reflectivity to some extent.     

Physical weathering of marbles caused by anisotropic thermal expansion

 Marbles as building stones as well as in their natural environments show complex weathering phenomena. The most important damage scenario is based on the highly anisotropic thermal expansion coefficient α of calcite, i.e. extreme expansion parallel and contraction normal to the crystallographic c-axis. Therefore, the rock fabric and especially the lattice-preferred orientation (texture) of calcite and/or dolomite as the predominant mineral phases in marbles have a significant influence on the mechanical weathering. The textures of marbles from five different locations vary from a more or less perfect prolate to moderate oblate shape of the [006] pole figure tensor. Accordingly, the texture-derived bulk thermal dilatation anisotropy covers a broad range from –0.048 to 0.680. The modelled thermal dilatations correlate with those obtained from experimental measurements. The difference in magnitude is basically explained by the microcrack fabrics which was not considered in the computations. All samples show a deterioration due to thermal treatment regardless of the strength of texture. The directional dependence of (a) the total magnitude of the thermal dilatation coefficient and (b) of the residual strain is highest in marbles with a strong texture, whereas the Carrara marble with a weak texture exhibits a uniform crack formation. The progressive loss of cohesion along grain boundaries due to dilatancy may serve as an example for the initial stage of physical weathering. Received: 10 February 1999 / Accepted: 16 October 1999     

Texture development of recrystallised quartz polycrystals unravelled by orientation and misorientation characteristics

The development of microstructures and textures (i.e. crystallographic preferred orientations) during recrystallisation of naturally deformed quartz polycrystals has been studied via electron diffraction techniques in the scanning electron microscope. In the investigated sample series of quartz-rich rocks originating from different deformation regimes, the microstructural and textural changes in quartz have been significantly influenced by dynamic recrystallisation. Based on microstructural observations paired with orientation and misorientation analyses down to the scale of grains and subgrains, criteria could be established which characterise the dominant recrystallisation process and its influence on texture development. It is shown that the texture development during dynamic recrystallisation is controlled by a differential activation of slip systems in grains of ‘soft’ and ‘hard’ orientations. The analyses provide further evidence that specific grain orientations are preferred during crystal plastic deformation, recrystallisation and grain growth. The influence of twinning after the Dauphiné law was also investigated. Observations of a progressive reduction in the population of Dauphiné-twin boundaries during recrystallisation and a penetrative deformation in both hosts and twins indicate a generation prior to deformation and recrystallisation. A mechanical origin for twinning and possible influence on texture development was therefore discarded.