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1.
对攀枝花钒钛磁铁矿尖山矿区的细粒和中粒辉长岩进行了单轴压缩、常规三轴压缩、抗拉强度和软化等系列岩石力学试验,研究了岩石结构(矿物颗粒大小)、水和围压等因素对岩石强度和变形特性的影响。结果表明,细粒辉长岩单轴抗压强度、弹性模量和压拉比均高于中粒辉长岩,但在三轴压缩情况下,两种岩石的峰值强度、残余强度和弹性模量差异较小;与中粒辉长岩相比,细粒辉长岩的峰值强度的黏聚力C较大,而峰值强度的内摩擦角φ较小;随着围压的增长,辉长岩峰值强度、残余强度与围压近似呈线性关系,剪切破坏角减小,平均模量E增长不明显,割线模量E50增长较显著;辉长岩的软化系数较高,在水的作用下弹性模量降低,泊松比升高。 相似文献
2.
黏土的变形主要受土颗粒之间的联结方式控制,将土颗粒之间的联结方式分为完善联结和滑动联结。在弹性变形阶段,颗粒之间的联结为完善联结,随着剪应力的增大,骨架中一部分完善联结逐渐变成滑动联结,这种转变即为损伤的演化。骨架的损伤和破坏遵循Mohr-Coulomb准则,在p-q平面中以应力点到初始损伤线和破坏线的相对距离表示损伤比,给出了一种描述骨架损伤和计算损伤演化的方法,进而提出了一种描述黏土在不排水条件下剪切变形的损伤本构模型。模型中的参数可根据常规三轴压缩试验确定,模型的形式简单,可适用于复杂的应力路径情况。对试验结果的拟合表明,该模型能较好地反映黏土在不排水条件下的剪切变形特征。 相似文献
3.
Biaxial experiments are performed with rod assemblies to study the micro-mechanical deformation behavior of granular materials. The focus of these experiments is upon the micromechanical behavior under mixed boundary conditions, with stress-controlled lateral boundaries and displacement-controlled axial boundaries. Particle motions, i.e. displacements and rotations, are measured during the test. The particle motions are analyzed to study deformation patterns, including shear localization. Deformation patterns in a number of rod assemblies with random packing structures are investigated. 相似文献
4.
The morphology and internal structure of individual olivine grains from ultramafic rocks in the Guli and Gal’moenan dunite
massifs differing in origin are considered. To restore the ontogeny of mineral aggregates, traces of elastic deformation retained
in mineral grains have been used. Comparison of anatomy of olivine grains from these two massifs showed that the mechanism
of accommodation of rocks to changing geological settings is expressed as the response of the mineral aggregate structure
and variation in the anatomy of individual mineral grains. At the level of individual grains, this is annihilation of older
defects and origination of younger dislocations; refinement of the crystal lattice; exsolution; formation and transformation
of new mineral phases; and creep and migration of subboundaries within grains. At the aggregate level, this is rotation and
migration creep of the internal boundaries of rock; formation of new boundaries of mineral intergrowths; reorientation of
boundaries; and variation in their extent, density, and grain dimensions. The prehistory of massifs controls the manifestation
and abundance of various elastic deformations and related types of recrystallization of olivine grain boundaries and subboundaries
in aggregates. New conditions and accommodation of mineral aggregates to these conditions have instigated specific schemes
of recrystallization, which bear information on the history of rocks and their massifs. 相似文献
5.
This paper is intended to give some information about how to build a model necessary for bending analysis of rectangular and circular plates resting on a two‐parameter elastic foundation, subjected to combined loading and permitting various types of boundary conditions. The formulation of the problem takes into account the shear deformation of the plate and the surrounding interaction effect outside the plate. The numerical model based on an 18‐node zero‐thickness isoparametric interface element interacting with a thick Reissner–Mindlin plate element with three degrees of freedom at each of the nine nodes, which enforce C0 continuity requirements for the displacements and rotations of the midsurface, is proposed. Stiffness matrices of a special interface element are superimposed on the global stiffness matrix to represent the stiffening elastic foundation under and beyond the plate. Some numerical examples are given to illustrate the advantages of the method presented. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
6.
The mechanical properties of cohesionless granular materials are evaluated from grain‐scale simulations. A three‐dimensional pack of spherical grains is loaded by incremental displacements of its boundaries. The deformation is described as a sequence of equilibrium configurations. Each configuration is characterized by a minimum of the total potential energy. This minimum is computed using a modification of the conjugate gradient algorithm. Our simulations capture the nonlinear, path‐dependent behavior of granular materials observed in experiments. Micromechanical analysis provides valuable insight into phenomena such as hysteresis, strain hardening and stress‐induced anisotropy. Estimates of the effective bulk modulus, obtained with no adjustment of material parameters, are in agreement with published experimental data. The model is applied to evaluate the effects of hydrate dissociation in marine sediments. Weakening of the sediment is quantified as a reduction in the effective elastic moduli. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
7.
Marianne Negrini Holger Stunitz Alfons Berger Luiz F. G. Morales 《Contributions to Mineralogy and Petrology》2014,167(3):1-22
We performed high strain (up to 47 %) axial compression experiments on natural quartz single crystals with added rutile powder (TiO2) and ~0.2 wt% H2O to investigate the effects of deformation on the titanium-in-quartz (TitaniQ) geothermobarometer. One of the objectives was to study the relationships between different deformation mechanisms and incorporation of Ti into recrystallized quartz grains. Experiments were performed in a Griggs-type solid-medium deformation apparatus at confining pressures of 1.0–1.5 GPa and temperatures of 800–1,000 °C, at constant strain rates of 1 × 10?6 or 1 × 10?7 s?1. Mobility of Ti in the fluid phase and saturation of rutile at grain boundaries during the deformation experiments are indicated by precipitation of secondary rutile in cracks and along the grain boundaries of newly recrystallized quartz grains. Microstructural analysis by light and scanning electron microscopy (the latter including electron backscatter diffraction mapping of grain misorientations) shows that the strongly deformed quartz single crystals contain a wide variety of deformation microstructures and shows evidence for subgrain rotation (SGR) and grain boundary migration recrystallization (GBMR). In addition, substantial grain growth occurred in annealing experiments after deformation. The GBMR and grain growth are evidence of moving grain boundaries, a microstructure favored by high temperatures. Electron microprobe analysis shows no significant increase in Ti content in recrystallized quartz grains formed by SGR or by GBMR, nor in grains grown by annealing. This result indicates that neither SGR nor moving grain boundaries during GBMR and grain growth are adequate processes to facilitate re-equilibration of the Ti content in experimentally deformed quartz crystals at the investigated conditions. More generally, our results suggest that exchange of Ti in quartz at low H2O contents (which may be realistic for natural deformation conditions) is still not fully understood. Thus, the application of the TitaniQ geothermobarometer to deformed metamorphic rocks at low fluid contents may not be as straightforward as previously thought and requires further research. 相似文献
8.
Magmatic zircons within two sheared gabbroic dykes from the peridotitic massif of Lanzo (Western-Alps, Italy) revealed evolution of deformation from crystal plasticity to rigid body rotation during shear zone evolution. This is the first time that multiple zircon grains have been analysed in a kinematic context in a shear zone. Zircon grains recorded crystal plastic deformation activating the commonly inferred <100>{001} and <001>{100} glide-systems to the newly identified <001>{110} glide-system. The exact selection of glide-system could be dependant of deformation conditions such as pressure, temperature, and strain rate. Moreover, the activation of one or several glide-systems within a single grain could be favoured by the primary orientation of the grains combined with a high strain rate. In these sheared gabbros, the deformation mechanisms evolve from plastic deformation at low strain rate conditions to increase strain, strain softening and localisation of deformation. The progressive shear zone development and the softening of the matrix relative to the zircon has lead to a switch from crystal-plasticity to rigid body rotation of zircon. The zircon grains rigid body rotation involved that their long axes became parallel to the lineation of the shear zone, causing reorientation and dispersion of the misorientation axes away from kinematic Y. 相似文献
9.
10.
In situ observations of polycrystalline ice deformed in simple shear between −10 and −1°C are presented. This study illustrates the processes responsible for the deformation, the development of a preferred crystallographic orientation and the formation of a preferred dimensional orientation. Intracrystalline glide on the basal plane, accompanying grain rotations and dynamic recrystallization, helps to accommodate the large intragranular strains. These are the most important mechanisms for crystallographic reorientation and produce a stable fabric that favours glide on the basal plane. Localized kinks, developed in grains unfavourably oriented for easy glide, are unstable and are overprinted by dynamic recrystallization. Dynamic recrystallization is a strain softening process with nucleation occurring in the form of equiaxed grains that grow subparallel to pre-existing grain anisotropies and become elongate during deformation. Plots of grain axial ratio against orientation (
) indicate a weak shape fabric which does not correspond to the theoretical foliation and elongation for the appropriate increment of shear strain. We argue that estimates of the strain magnitude made from orientation of elongate grains are unreliable in high temperature shear zones. These results are applicable to both geological and glacial shear environments. 相似文献
11.
The behaviour of dry and cohesionless granular material during quasi-static cyclic shearing under a constant normal stiffness (CNS) condition is theoretically studied. A particular attention is laid to the volumetric strain change and the degradation of the shear resistance in the course of shearing. Numerical calculations are carried out for several shear cycles under boundary conditions which are relevant to investigate the shear interface behaviour. The global and local evolution of deformation, stress and density within the granular material is investigated with a finite element method on the basis of a hypoplastic constitutive model extended by micro-polar quantities: rotations, curvatures and couple stresses. A mean grain diameter is used as a characteristic length of micro-structure. The constitutive equations for stresses and couple stresses take also into account the effect of the evolution of the void ratio, pressure dependent relative density, direction of rate of deformation and rate of curvature. The numerical results are qualitatively compared with corresponding laboratory tests on direct wall shearing performed by DeJong, Randloph and White. In addition, the results for cyclic shearing of an infinite granular layer between two very rough boundaries under CNS conditions are also enclosed and discussed. 相似文献
12.
Paul H. Reitan 《Lithos》1977,10(2):121-128
Metamorphic crystallization necessitates nucleation of new grains. Associated with this process is an energy barrier which requires an input of energy sufficient to make the net change of free energy with nucleus growth decrease so that the process of grain crystallization will proceed. Temperature increase and elastic strain are widely accepted as capable of including metamorphic crystallization. Evaluation of these suggests that an energy input on the order of 0.x cal gm?1 is commonly enough to overcome the energy barrier and induce metamorphic crystallization. Both processes are necessarily timebound to the time of energy input. Conservative quantitative evaluations of the increase in interfacial free energy by grain size reduction, and of the energy increase resulting from increased dislocation density of grains, show that energetically, these may be equally capable of inducing metamorphic crystallization. These processes can store energy in the system; later release of that energy by metamorphic crystallization may occur under stress and temperature conditions much different from those that accompanied the input of the energy. Furthermore, the formation of a new set of grains will necessarily eliminate the evidence of the precursor state, whether fine granulation or a condition of high dislocation density in the grains of the system.Experiments have demonstrated the existence and properties of tiny short-lived hot spots on the surfaces of sliding solids. From this we infer the likelihood of such high spot temperatures being realized at grain boundaries during penetrative deformation. The energy concentrated at these spots may help to overcome the energy barrier to nucleation and grain growth and may stimulate formation of stable grains and the progressive elimination of metastable grains during deformation. This is a syntectonic process, but recognizing that syntectonic metamorphic crystallization is most characteristic of regionally dynamothermally metamorphosed terranes, the importance of grain boundary hot spots in providing energy for metamorphic crystallization may be very great. 相似文献
13.
在工程荷载范围内,不计骨架颗粒的变形,骨架的变形实际是颗粒接触面变形的总和。当剪应力达到某个临界值时,黏性土骨架中有一部分颗粒接触面开始滑动,随着剪应力的增大,出现滑动的颗粒接触面的取向范围也会扩大。将这种颗粒接触面的滑动视为一种损伤。在损伤阶段,黏性土骨架中既有未滑动的接触面,也有已滑动的接触面,宏观剪切模量是这两种接触面的剪切模量的加权平均。在 平面中,根据应力圆与颗粒起始滑动包络线的相对位置,计算出已出现了滑动的颗粒接触面的取向范围,并定义该取向范围与其所能达到的最大值（由破坏时的应力圆计算）之比为骨架的损伤比。按损伤比进行加权平均得到骨架的整体剪切模量。模型中的参数完全可以根据常规三轴试验确定,模型的形式简单,可适用于复杂的应力路径。对试验结果的拟合表明,该模型能较好地反映黏性土在固结不排水条件下剪切变形的主要特征。 相似文献
14.
One of the goals of using the Global Positioning System (GPS) and other geodetic survey techniques in tectonics has been to detect boundaries such as faults or shear zones between rigid or mildly deforming crustal masses. The calculation of infinitesimal strains and rotations with GPS data has been widely used to detect shear zones but it has been largely unsuccessful because infinitesimal strain and rotation, although useful in many other ways, is non-diagnostic of shear zones or faults. Our approach is to work with components of deformation, not strain, and to design specifically a diagnostic method of detecting shear zones. This paper introduces the first part of our method, the detection of two-dimensional, strike-shift shear zones (MODES-2D). The MODES-2D method has three elements: (1) determination of the orientation of a suspected strike-shift shear zone by analyzing components of a deformation tensor derived from a data set of displacements in an arbitrary coordinate system; (2) resolution of the deformation tensor into the coordinate system parallel and normal to the detected shear zone; and (3) exploration of the resolved data set for evidence for a belt of inhomogeneous deformation, which is an essential characteristic of a shear zone. The operation of MODES-2D is illustrated herein with a theoretical survey network across an ideal shear zone developed with a buried dislocation-fault and with a survey network afforded by the crossing of the Kaynaşlı viaduct by the 1999 Düzce–Bolu earthquake rupture in Turkey. 相似文献
15.
Recent developments in the application of x-ray micro-tomography in laboratory geomechanics have allowed all the individual
grains of sand in a test sample to be seen and identified uniquely in 3D. Combining such imaging capabilities with experiments
carried out “in situ” within an imaging set-up has led to the possibility of directly observing the mechanisms of deformation
as they happen. The challenge has thus become extracting pertinent, quantified information from these rich time-lapse 3D images
to elucidate the mechanics at play. This paper presents a new approach (ID-Track) for the quantification of individual grain
kinematics (displacements and rotations) of large quantities of sand grains (tens of thousands) in a test sample undergoing
loading. With ID-Track, grains are tracked between images based on some geometrical feature(s) that allow their unique identification
and matching between images. This differs from Digital Image Correlation (DIC), which makes measurements by recognising patterns
between images. Since ID-Track does not use the image of a grain for tracking, it is significantly faster than DIC. The technique
is detailed in the paper, and is shown to be fast and simple, giving good measurements of displacements, but suffering in
the measurement of rotations when compared with Discrete DIC. Subsequently, results are presented from successful applications
of ID-track to triaxial tests on two quite different sands: the angular Hostun sand and the rounded Caicos Ooids. This reveals
details on the performance of the technique for different grain shapes and insight into the differences in the grain-scale
mechanisms occurring in these two sands as they exhibit strain localisation under triaxial loading. 相似文献
16.
It is suggested that the kinematic framework controls the orientation of crystallographic fabrics developed in plastically deformed quartzites. Important directions in this framework are those of the instantaneous stretching axes, and the flow plane and flow direction if these can be uniquely defined. Rotation of the crystal axes takes place at any instant of time dependent on the orientation of the grain relative to the stretching axes. Because of this dependence the skeletal outline* of a pattern of preferred orientation is sensitive to the closing stages of deformation. Thus fabrics measured in major movement zones cannot be related to early thrust or shear displacements without considering the effects of the geological history subsequent to those events.Nevertheless, asymmetric fabrics in movement zones may allow determination of the shear direction and sense of shear. Asymmetry in the intensity distribution is less susceptible to modification than asymmetry in the fabric skeleton, and may remain as a persistent measure of the sense of shear in mylonites subjected to coaxial deformation after non-coaxial events. However, fabric asymmetry need not always be related to the deformation history, and effects related to the population of initial grain-orientations must be considered, as well as the influence of recrystallization and grain growth.A problem of scale is involved in extrapolating the movement picture inferred from the behaviour of a few hundred crystal grains to larger dimensions. This question is also encountered when trying to specify deformation paths in mesoscopic shear zones. It is difficult to obtain simple shear experimentally because of the role discontinuities play in deformation. In certain cases in natural shear zones the quartz grains may be subjected to a coaxial deformation path while the bulk deformation is progressive simple shear. Caution must therefore be exercised when attempting to use quartz fabrics to infer characteristics of the bulk kinematics or movement picture applicable during deformation. 相似文献
17.
S. White 《Contributions to Mineralogy and Petrology》1979,70(2):193-202
The results are reported of a combined optical and electron microscopy study of microstructural variations across a quartz
mylonite zone with increasing shear strain. The mylonite developed by recrystallization of the deformed quartz grains with
increasing shear strain. It was found in a given specimen that the size of recrystallized grains and of sub-grains were always
smaller in electron micrographs. The possible reasons for this are discussed. The size of both features decreased with increasing
shear strain irrespective of the microscope used. However the density of unbound dislocations remained constant. A marked
grain size reduction occurred in phyllosilicate rich layers. Variations in sub-grain size were observed within the relict
old grains which remained at low shear strains. These are thought to reflect stress intensification adjacent to grain boundaries
during deformation. The relict grains recrystallized at higher strains. Stresses were estimated from grain and sub-grain sizes
and from the dislocation density. The results indicate that estimates based on grain size are unreliable if phyllosilicates
inhibit the growth of grains during recrystallization, and that the dislocation densities are altered during uplift and are
unlikely to give meaningful estimates. It is also concluded that the microstructures reflect stress gradients present during
the formation of the mylonite, that is the initiation and propagation of the shear zone and that these were subsequently replaced
by strain rate gradients. 相似文献
18.
A methodology has been developed to extend the incremental (Eulerian) Digital Image Correlation (DIC) technique to enable a Lagrangian‐based large‐strain analysis framework to examine the nature of strain and kinematic nonuniformity within shear bands in sands. Plane strain compression tests are performed on dense sands in an apparatus that promotes unconstrained persistent shear band formation. DIC is used to capture incremental, grain‐scale displacements in and around shear bands. The performance of the developed accumulation algorithm is validated by comparing accumulated displacements with two sources of reference measurements. A comparison between large and infinitesimal rotation is performed, demonstrating the nature of straining within shear bands in sands and the necessity of using a finite strain formulation to characterize ensuing behavior. Volumetric strain variation along the shear band is analyzed throughout macroscopic postpeak deformation. During softening, volumetric activity within the shear band is purely dilative. During the global critical state, the shear band material is seen on the average to deform at zero volumetric strain; however, locally, the sand is seen to exhibit significant nonzero volumetric strain, putting into question the current definition of critical state. At the softening‐critical state transition, a spatially periodic pattern of alternating contraction and dilation along the shear band is evidenced, and a preliminary evaluation indicates that the periodicity appears to be a physical phenomenon dictated only in part by median grain size. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
19.
基于线弹性断裂力学裂隙面张开位移及剪切位移理论公式,考虑裂隙存在常法向和常切向刚度情况,研究了含单个裂隙岩体加载过程中由于裂隙存在而附加的弹性应变能。基于应变能等效方法并假设两种裂隙变形模型--非均匀变形模型和均匀变形模型,研究了二维非贯通裂隙岩体的等效杨氏模量和等效剪切模量解析表达式。研究结果表明,对于贯通裂隙规则分布情况,均匀变形模型得到的解析解与Amadei等的结果一致;对于非贯通裂隙正态分布情况,考虑裂隙相互作用的非均匀变形模型解明显低估裂隙岩体的等效杨氏模量和等效剪切模量,而考虑裂隙相互作用的均匀变形模型解与有限元数值解的偏差在10%以内。得到的解析表达式在一定条件下可以作为裂隙岩体等效弹性模量评价方法之一。 相似文献
20.
Quartz deformation bands are kink bands in quartz crystals. A deformation band develops as a region of localized crystal-plastic deformation with boundaries perpendicular to the slip plane and slip direction, which usually is along an -axis in the basal plane. Under cross-polarized light, the difference in crystallographic orientation between a deformation band and its host is indicated by a difference in extinction positions. The displacement between the c axis in a deformation band and the c axis in the host represents the angular shear of the deformation band in the direction of the c axis in the host grain. Assuming the deformation is homogeneous at the grain scale, the angular shear of the grain (the gauge) is calculated by multiplying the angular shear of the deformation band by the ratio of the sheared part to the whole grain. Using the strain-gauge method for three-dimensional infinitesimal strain analysis, a minimum number of five grains measured on universal stage is needed to solve for the deviatoric strain components of the aggregate if the strain is homogeneous in the aggregate. Data from more than five grains are used to find the best-fit strain components by a least-squares method. The principal strains and their orientations are found from these strain components by calculating the eigenvalues and eigenvectors. A 3-D strain ellipsoid also is obtained from strain ellipses in three perpendicular planes determined from the two-dimensional flat-stage measurements by the Wellman method. Both the strain-gauge method and the Wellman method are tested by using synthetic data sets and applied to a naturally deformed sample. Both methods give similar results; the established Wellman method thus confirms the strain-gauge calculation. 相似文献