Preferred Orientation Of Grains Research Articles

Fabric-Property Relationships in Fine Granular Materials

AbstracV In this investigation fabric-property relationships were studied in a silty fine sand sized crushed basalt- an artificial 'soil' that has previously been used to simulate lunar soil. The fabric was characterized by measuring preferred orientations of grains, and pore size distribution was determined by mercury intrusion porosimetry. When deposited by pouring, the grains acquired strong preferred orientations in the horizontal direction and formed pores between 1 and 30 #m dia. Densification by static or dynamic compaction resulted in near random grain arrangement and pore sizes between 0.1 and 10 ~m dia. Strength in direct shear and one-dimensional compressibility with the associated lateral stresses were measured. The strength was up to 30 per cent higher when the sample was sheared normal to the preferred orientation of grains than when the shearing was parallel to the orientation direction. This is to be expected, as shearing across the preferentially oriented grains should involve breakage or reorientation of many grains. At a given initial void ratio the compressibility of statically compacted specimens was larger (up to 30 per cent higher axial strain) than that of dynamically compacted specimens at very low stresses. At higher stresses both samples exhibited equal compressibility, suggesting that the grains become more randomly arranged at low void ratios (comparing samples of equal initial void ratios).

Petrography and Diagenesis of Franciscan Limestones

ABSTRACT Lithification of Franciscan limestones did not occur immediately after deposition as demonstrated by the preferred orientation of grains which is a result of compaction. Variable preservation of grains in adjacent layers of Laytonville Limestone are a result of variable degrees and different times of lithification; less compacted layers containing better preserved grains were lithified earlier than the more compacted layers. Recrystallization of the micrite followed burial and compaction of the limestone. All degrees of recrystallization are found in the coccoliths that originally composed at least 50 percent of the micrite. During advanced stages of recrystallization, coccoliths and other grains were transformed to a continuous and uniform calcite mosaic. At this stage the primary po osity of the sediment was removed and the sediment became completely lithified. Stylolites probably formed over a long period of time that started when the limestones were unlithified. Remnants of stylolites are found within the chert and stylolites are common at the margins of chert bodies. Most stylolites are younger than veins. Chert formed only in micritic limestones containing Radiolaria. The silica eventually replaced the original carbonate micrite between the radiolarian tests and the end result of this replacement was transformation of a limestone bed to chert.

The influence of some geometrical and physical factors on the diffraction patterns of polycrystals

A method of grain size determination in polycrystals from the number of spots on Debye-Scherrer rings serves here as experimental basis for the study of the influence of a) parameters of the experimental arrangement (e.g., divergence of primary beam, choice of the standard blackening and ratio of exposures), and b) properties of the specimen (e.g., preferred orientation of grains and their local distribution of sizes), on the results of measurement. Sufficiently numerous statistical sets of experimental data show that the counting of spots may be quite exact, but the usually applied relation between the number of spots and grain size is likely appreciably oversimplified. As the assumptions, from which the mentioned relation was deduced, are closely connected with problems of X-ray diffraction, the results presented in this paper may be interesting from a more general point of view. The X-ray results are also compared to the metallographic ones.

Quantitative Correlation between Preferred Orientation of Grains and Elastic Anisotropy of Marble

In recent years the dependence between the propagation of elastic waves in anisotropic rocks and the preferred orientation of grains in the rocks has been under intensive study. The disadvantage of the conventional visual comparison of both quantities in graphical representation is the impossibility of quantitatively expressing the assumed similarity. In this respect, by using the cross-correlation approach, the authors have improved on this. According to the quite different character of both quantities, and to the special properties of the range of definition (sphere), a new method was needed for computing the cross-correlation function. This paper deals with experimental data processing and with determining the form of the cross-correlation function. The proposed method was successfully proven on a sample of marble. In the case investigated, the maximum value of the cross-correlation function corresponded to a mutual angular shift of the correlated quantities by approximately 15°.

Origin of ultrabasic inclusions in basalts in southern Far East

The mode of occurrence, fabric, mineralogical and chemical features of ultrabasic inclusions in basalts of the South Far East are discussed in detail and compared with similar inclusions from various parts of the world. The inclusions occur mostly in alkalic varieties of basalt and commonly have cataclastic fabrics exhibiting preferred orientation of grains. They consist principally of olivine, enstatite or bronzite, chrome-diopside and spinel. Except for spinel, the compositions of the minerals are remarkably similar on a world-wide basis, whereas the enclosing rocks are represented by a variety of alkalic basalts. Chromium content of the inclusions is usually high compared to very low values for enclosing basalt. It is concluded that such inclusions are xenoliths of ultrabasic rocks rather than indigenous crystal differentiates. Their most plausible derivation is from the peridotite layer. This hypothesis explains their consistent composition, their association with deep rifts, the undifferentiated natu...

Transition rates of KNO 3 high-pressure polymorphs

A beryllium pressure vessel mounted in an X-ray goniometer and modified for heating to 300°C has permitted the direct recording of transition rates across all of the equilibrium boundaries of the KNO 3 phase diagram. Most transitions show rate curves that taper off near the completion of the process, but metastable persistance of phase III occurs in the phase II field and becomes greater at high pressures and low temperatures along the negative II–III phase boundary. Several diffraction patterns of the transitions I–II and III–II revealed preferred orientation of grains in the resulting aragonite-type phase. Cell parameters of KNO 3-I and KNO 3-III (both modified calcite-type structures) taken in their stability fields show a marked reduction in the c-axis length going from phase I to phase III with increasing pressure at constant temperature.

Induced Magnetic Anisotropy Created by Magnetic and Stress Annealing of Iron-Aluminium Alloys

Polycrystalline samples of five iron-aluminium solid solutions were subjected to various heat treatments either (i) in a strong magnetic field, or (ii) under tensile stress. For treatment (i) the samples were in the form of cylinders, while in case (ii) they were machined into this form after stress treatment. Torqueazimuth plots were obtained from each sample by means of a torque magnetometer; further heat treatments were then applied, followed again by torque measurements, to permit correction for the intrinsic anisotropy resulting from unavoidable preferred orientation of grains. The maximum value of anisotropy, whether field- or stress-induced, arises at 21-22 at.% aluminium. Induced anisotropy energies of up to 17 000 erg cm-3 were recorded. A variety of heat treatments were used to explore the inhibiting effect of spontaneous long- or short-range order on the development of induced anisotropy. This inhibiting effect is pronounced, and in stoichiometric Fe3Al it is possible to prevent almost completely the creation of induced anisotropy. Such inhibition is to be expected if the induced anisotropy is caused by directional order. A close correspondence is observed between the composition dependence of induced anisotropy and that of the Zener internal friction.

Induced Magnetic Anisotropy Created by Magnetic or Stress Annealing of Iron-Aluminum Alloys

Polycrystalline samples of five iron-aluminum solid solutions were subjected to various heat treatments(1) in a strong magnetic field, or (2) under tensile stress. For treatment (1) the samples were in the form of cylinders, while in case (2) they were machined into this form after stress treatment. Torque-azimuth plots were obtained from each sample by means of a torque magnetometer; further heat treatments were then applied, followed again by torque measurements, to permit correction for the intrinsic anisotropy resulting from unavoidable preferred orientation of grains. The maximum value of anisotropy, whether field or stress induced, arises at 21–22 at. % aluminum. Induced anisotropy energies of up to 17000 ergs/cm3 were recorded. A variety of heat treatments were used to explore the inhibiting effect of spontaneous long- or short-range order on the development of induced anisotropy. This inhibiting effect is pronounced, and in stoichiometric Fe3Al it is possible to prevent almost completely the creation of induced anisotropy. Such inhibition is to be expected if the induced anisotropy is caused by directional order. A close correspondence is observed between the composition dependence of induced anisotropy and that of the Zener internal friction.

ON THE APPEARANCE OF A PECULIAR SURFACE LAYER WITH COARSE GRAINS BY THE ANNEALING OF 3S SHEET

Various properties of 3S sheet when it was heated in air furnace or salt bath and a structure of its alloy slab were examined. The results obtained were as follows:(1) When 3S sheets, having each thickness 3.2mm (cold reduction degree 46%), 1.6mm (72%), 0.8mm (84%), were annealed in the air furnace, we found that a peculiar surface layer consisted of the very coarse grains had appeared on them. The grains of such surface layers were coasser as the annealing temperature lower and smaller as the heating velocity faster. Also the grain size was maximum near 70% cold reducion degree. In the case of salt bath heating, the difference of grain sizes between surface and inner part could not be seen and the grains were smaller than any ones of the air furnace heating.(2) The thickness of the surface layer was very thin such as only 2% of the sheet thickness and each about 0.06mm (3.2mm sheet), 0.03mm (1.6mm), or 0.01mm (0.8mm). If this layer appeared once, it did not disappear although the sheet was rolled to 0.1mm. And even specimens with such thin peculiar surface layers exhibited orange peal by deep drawing.(3) The surface layer had the higher recrystallization temperature, the lower hardness than inner part and also the distribution of hardness or grain size changed suddenly at certain depth same to the layer thickness, it was hardly etched, probably due to the homogeneous distribution of working stress.(4) As to the microstructure of sheet, Mn compound particles in the surface layer were smaller and distributed homogeneously, but larger and heterogeneous in the inner part. Then, the dispersoid only could be seen in the inner part.(5) The structure of slab surface chilled at the face of metallic mould exhibited the very coarse grains involving the small particles of Mn compound and no dispersoid, but the inner structure appeared with the small grains involving the large particles of Mn compound and a great number of dispersoid. The slab structure like this was proportional to the sheet structure.(6) The sheet worked by cold rolling after preheating at 550°×15hrs exhibited the very small recrystallized grains, perhaps owing to the appearance of dispersoid in surface or inner part.(7) The growth of the peculiar surface layer and the grosscrystallization of recrystallized grains in it were thinked separately through these results.a) As for the growth of the surface layer, the surface is deformed by hot rolling more severely than the inner pard and softened with the heat formation by this severe deformation. This also the crystal orientations of grains are ordered gradually. By cold rolling the surface is deformed more and more with a partially heterogeneous rolling action and the crystal orientation is ordered strongly. Through this process the difference of various properties between surface and inner part will appear as described above.b) About the grosscrystallization of surface grains, we think that a incubating coarsen property of Mn in the alloy will be a important factor for grain growth and this characteristies of Mn will be promoted by the following facters such as: the surface structure of casting, the strongly preferred orientation of grains in the surface layer with particularly severe deformation, and the working process the dispersoid do not appear through rolling period.(8) In order to the grains, preheating prior to the finishing rolling or salt bath heating was effective.

Initial Shape and Roundness of Sedimentary Rock Mineral Particles of Sand Size

Measurements have been made of size, circularity (two dimensional sphericity) and roundness of crushed and screened fragments of nine minerals of sand size commonly found in sedimentary rocks. These are regarded as initial size, shape, and roundness before abrasion in ball mills. These are calcite, andalusite, quartz, garnet, zircon, tourmaline, microcline, sillimanite, and hornblende. While abrasion modifies shape of grains, the end shape ... appears to be determined by its original (See Pettijohn, 1949, p. 54.) It was found that each mineral possesses its own set of characteristics. These are related to type of cleavage and tenacity possessed by each mineral, but relationships are not simple. Sizing by screening introduces an element of shape. Similarly, microscopic measurements reflect a different aspect of shape due to preferred orientation of grains on slide. Such measurements are essentially two dimensional. The frequency distribution is given as per cent by number, so results may be more applicable to similar measurements in study of sedimentary rocks in form of thin section. A discussion of various methods is given Studies of abrasion of minerals in laboratory apparatus, such as ball mills, should recognize that each mineral has its own characteristics. Details of these differences are shown in table 9.