90/50 verniom

B10,doi The biotite foliation in the Four-mile gneiss results in dilatancy and strength anisotropies, which become more pronounced with increasing confining pressure. Microstructural observations indicate that when there 90/50 verniom high resolved shear stress on the macroscopic foliation, dilatancy arises from extensile microcracks nucleated by frictional slip on biotite grains. Evolution of crack geometry and coalescence are also influenced by the biotite foliation.

Motivated by these observations, a damage mechanics model based on sliding wing cracks was adopted to analyze the anisotropic development of dilatancy and brittle fracture.

Frictional bir kişi yüksek tansiyon için ne yapmalı for the sliding cracks are inferred to be comparable to those of cleavage surfaces of biotite. The strength anisotropy data of the Four-mile gneiss can be explained by the variation of the initial damage with 90/50 verniom foliation angle.

The damage derives from a set of preexisting microcracks with random orientation, and a set of cleavage cracks in mica grains preferentially oriented along the foliation angle.

Hence, the initial damage is higher for the intermediate angles, and, consequently, the strength is somewhat lower.

The observation that the mechanical strengths of a variety of foliated rocks decrease with increasing mica content can be explained by the same model, with the implication that the initial damage and mica content are linearly related.

The mechanical and microstructural data show that 90/50 verniom anisotropy may significantly influence the progressive development of borehole breakout and strain localization. Baud, and T. Wong, Dilatancy, brittle strength, and anisotropy of foliated rocks: Experimental deformation and micromechanical modeling, J. Introduction nisms, depending on how stress is applied relative to the anisotropy planes.

Illustrative examples were provided by [2] The phenomenon of mechanical anisotropy has Donath [] on slate, Paterson and Weiss [] on received considerable interest in rock physics and structural phyllite, and Kronenberg et al.

Bedding in sedimentary rocks, cleavage in slates, biotite. Elastic anisotropy of a rock can [3] One of the objectives of this work is to address the be related to its fabric, a seismic manifestation of which is interrelationships of textural anisotropy, dilatancy, and the shear wave splitting [e. Dilatancy, defined price, ; Siegesmund et al.

Textural anisotropy as inelastic volume increase, is universally observed as a can also result in significant anisotropy of tensile [Nova and precursor to the inception of shear localization in the brittle Zaninetti, ; Liao et al. The Donath, ; Borg and Handin, ; Vernik et al. It is recognized that the microcracks Copyright 90/50 verniom the American Geophysical Union.

To our knowledge, the onset and development of dilatancy in foliated rocks have not been systematically investigated. Notwithstanding the paucity of laboratory data, assumption of dilatancy anisotropy has been implicitly 90/50 verniom explicitly incorporated into the interpretation of borehole breakouts and in situ stress measurements [e.

It may also play a significant role in the localization of strain in retrograde shear zones [e. They defined a three-dimensional failure envelope with orthorhombic characteristics that is related to the symmetry of the foliation and lineation of biotite within the rock. In this study we investigated the anisotropic mechanical behavior of the Four-mile gneiss by conducting triaxial compression experi- ments with volumetric strain and AE measurements, as well Figure 1.

Reference scheme for sample orientation. Two related ques- tions are addressed in this study.

Is the critical stress for the muscovite. Plagioclase grains have lengths ranging from 0. If so, why and how is it to 2. Quartz and microcline grains are subequant, related to the peak stress anisotropy?

Biotite, the predominant phyllo- compressive 90/50 verniom has been analyzed by incorporating silicate, occurs as isolated grains, 0. Measured poles to biotite grains define a strong [Walsh and Brace, ]. More refined models have been maxima perpendicular to the macroscopic foliation.

Petro- proposed [e.

In this study, we adapted 90/50 verniom. The samples were cored in five orientations within a the damage mechanics model of Ashby and Sammis [] plane perpendicular to the macroscopic foliation and con- to analyze the observed mechanical anisotropy in terms of taining the lineation corresponding to the x — z plane crack nucleation around a preexisting weak phase and the defined by Gottschalk et al. Sample orientations influence of the preferred orientation of biotite on subse- are described by the angle b that specimen axis makes with quent damage accumulation.

Synthesis of our mechanical the foliation Figure 1. The porosities so measured for four state and mica content.

Ürün Değerlendirmeleri

The implications of our results for randomly selected samples ranged from 0. Hydro- related tectonic and geophysical processes will also be static compression data indicate that the crack porosity discussed.

Mechanical Deformation copper foil thickness 0. Sample Material and Preparation MPa to seat the jacket and collapse it tightly onto the [7] A detailed petrographic description and analysis of sample. One axial and one radial strain gauge of lengths 10 the 90/50 verniom gneiss were given by Gottschalk et al. The samples were further The axial, a Samples 90/50 verniom unloaded near the peak stress for microstructural 90/50 verniom and volumetric strains are plotted as functions of observations.

In this paper, compressive stresses and strains are considered to be positive. The onset of dilatancy C0 is marked by the stress level at which the differential stress — volumetric strain curve deviates from clamped to the steel end spacers with wire. Strain gauge linearity [Brace et al.

Ürün Bilgileri

A piezoelectric transducer PZT-7, 5. Preexisting cracks are not fully closed until the attached to one spacer to monitor AE activity during the application 90/50 verniom — MPa confining pressure.

Since tests experiments. The confining pressure was monitored with 90/50 verniom strain gauge pressure transducer with an accuracy of 0. The axial displace- ment was monitored with a displacement transducer between the ram and the fixed pressure vessel. The axial load was measured with an external load cell accurate to 1 kN.

The strain measurements have an accuracy of 0. The AE signals were conditioned by a preamplifier and the characteristics of the signal were screened with 90/50 verniom discriminator [see Wong et al.

Representative stress 90/50 verniom strain curves and acoustic microstructural observation. The yield stress and onset of dilatancy are also experiments that ended in brittle failure, and then unloaded.

Microstructural Observations of Deformed Samples [18] In general the deformation microstructure in the gneiss is similar to granite and other low-porosity crystalline rocks deformed in the brittle field [Tapponier and Brace, ; Wong, ; Kranz, ; Wong and Biegel, ; Hirth and Tullis, ; Chang and Haimson, ]. All 90/50 verniom failed along macroscopic faults formed by the growth and coalescence of extensile microcracks with a predominant orientation parallel to the maximum compres- sive stress.

The optical microscopy observations of Gott- schalk et al.

However, our SEM and optical microscopy Figure 3. The general form of the stress — strain curves and AE activity are similar at all b values. There is no systematic trend for the amount of dilatancy [19] Sample FMG2 was deformed to just beyond 90/50 verniom before failure to vary with b. However, there is a general onset of dilatancy C0. The most 90/50 verniom observation in decrease in the amount of dilatancy with increasing pres- this sample is that there is evidence for crack growth around sure.

This increase is due to the elastic closure of microcracks. There is appreciable sample-to-sample variability. To our knowledge, this is the first comprehensive set of data on the concomitant variation of C0 and brittle strength as functions of foliation orientation and confining pressure. The onset of dilatancy and peak stresses follow qualitatively similar trends in anisotropy.

The peak differential stresses and their variation with York Hastanesi Kardiyak Enstitüsü agree with the results of Gottschalk et al. These are typical of stress-induced microcracks [Tapponier and Brace, ; Kranz, ], with very low aperture-to-length ratios, smooth, parallel sides, essentially constant width, and very sharp terminations, often within grains.

Cadence Boya, Hobi ve sanat Malzemeleri

The biotite grain has probably undergone sliding on an open cleavage crack, but slip displacements along such sliding cracks are difficult to resolve even 90/50 verniom the SEM [Wong, ; Wong and Biegel, ]. Shear deformation in the biotite would cause a stress concentration at the end of the grain, which was relieved by the formation of tensile cracks.

Sample FMG4 was deformed to the stage at which a surge in AE activity indicated the imminent attainment of the peak stress. This sample shows intense zones of cracking around the tips of the grains Figure 5b. Most of the grain boundaries are cracked.

At this stress, kinking gebelik toksemisi begun in some of the biotite grains. Crack coalescence is more intense in sample FMG5 which was deformed to near the peak stress. See Kroanenberg et al. Figure 6a shows some of the complex kink geometries that develop in biotite grains oriented at low angles to the compression axis.

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Note especially the formation of voids and the tendency for the kink boundaries to trend diagonally across 90/50 verniom basal planes. Intense intragranular cracking in feldspar and quartz grains which probably resulted from elastic mismatch between the compliant biotite and the stiff feldspar or quartz in between can be seen. The elongate biotite grains often seem to act as barriers for the linkage of cracks across more than one grain Figure 6b. Crack Coalescence [22] The three samples loaded to near the peak stresses were examined under the petrographic microscope to char- acterize the geometry of crack coalescence.

The biotite grains appear to exert some degree of control on the geometry of the growing crack Figure 5. Direction of s1 was vertical, and biotite grains are localized in narrow zones that link the scale bar is 50 mm. The upper left of Figure 7b is typical.

Grain incipient linkage of cracks. Note the grain boundaries are boundary cracks appear to 90/50 verniom more common than intra- mostly cracked. Direction of s1 was vertical, and scale bar granular cracks. This may be due to the weak shape is mm. Quartz often occurs as subequant grains arranged in Arrays of dava yüksekse tansiyon cracks are also present.

Direction of s1 zones subparallel to 90/50 verniom foliation, and as a result, the was vertical, and scale bar is mm. Failure Mode of Biotite 90/50 verniom Previous studies have underscored the important role that crystal plastic processes in biotite play in triggering and controlling microcracking and shear localization in isotropic [Tapponier and Brace, ; Wong and Biegel, ; Chang and Haimson, ] and anisotropic [Gottschalk et al.

While our observations are in general agreement with previous work, we have noted several new and important features. In the relatively isotropic Westerly granite, Tapponier and 90/50 verniom [] only observed the opening of grain boundaries and healed cracks in samples deformed to just beyond C0. The absence of shear-related wing cracks is often cited as evidence against the use of a class of theoretical models formulated by Horii and Nemat-Nasser [], Ashby and Hallam [], and Kemeny and Cook [] for the onset and development of dilatancy 90/50 verniom brittle rock.

While shear-induced wing cracks were inferred to have propagated and Hamilelik sırasında düşük kalp hızı in failed samples of anisotropic rock similar to the Four-mile gneiss [Gottschalk et al. Note the Wong and Biegel, ; Gottschalk et al. Our complex geometry and inclination of kink bands relative to observations show that this is not universally true for all basal planes of the biotite.

Direction of s1 was vertical, and orientations in anisotropic rock. In particular, the biotite scale bar is 25 mm. Direction of s1 was foliation is oriented at high angles to the compression axis, vertical, and scale bar is mm.

To overcome such barriers and attain the critical orientations of kink bands relative to the compression axis damage geometry for the inception of shear localization, the were measured.