Set Of Grains Research Articles

Analysis of texture evolution in channel die compression—I. Effects of grain interaction

The effect of grain interactions on deformation patterns and texture evolution is examined by the finite element method for a particular set of grains deformed in channel die compression. The material behavior within each element is determined from a slip based constitutive formulation that fully accounts for finite deformations and lattice rotations with deformation. Compatibility and equilibrium are enforced across the grain boundaries, and grain boundary sliding is not permitted. In order to make the analyses numerically tractable, an idealized two-dimensional geometric model is used to model the deformation in the longitudinal-transverse plane; and the strains are assumed to be uniform through the compression direction. Boundary conditions simulating homogeneous plane-strain compression are applied to the model region. The results reveal complex deformation patterns arising from grain interactions. The analyses also show that the crystallographic texture and the spread of orientations within a grain depend not only on the orientations of the neighboring grains, but also on the constraints provided by grains located several grains away.

Computer simulated grain growth stagnation

The growth of a set of grains can be treated mathematically by a deterministic model, or alternatively a probabilistic method can be adopted. In this paper the linkages between these two different approaches are evidenced and hypotheses are advanced on the contact areas between the grains in a polycrystalline material, which are implicit in the Wagner-Zlyosov-Hillert dynamic grain growth model. Basic equations of the Hillert model in the presence of Zener drag describing grain growth and the grain size distribution shape have been numerically integrated. Relationships to be satisfied by parameters characteristic of the distribution and between the latter and the amount of inhibition have been determined under conditions of complete growth stagnation. Careful experimental measurements carried out on a Fe-3% Si material, under growth stagnation conditions, confirm the validity of theoretical equilibrium equations.

Packing in a clastic sediment: Concept and measures

Packing has been defined as the effective utilization of space by mutual arrangement of the constituent grains of an aggregate. The effective utilization of space is governed both by the material aspect of the constituent grains (size range, size ratio, shape, etc.) of a clastic sediment and the mechanism aspect (the manner of deposition) of the agent. Three new measures of packing have been introduced: (1) intrinsic packability factor ( P f) denoting the maximum packing attainable with a particular set of grains: (2) packing efficiency ( P c), denoting how far the agent is capable of attaining the said maximum; and (3) packing index ( P i), denoting the resultant of the material aspect and the mechanism aspect. For proper appreciation of the packing of a clastic sediment, all the three packing parameters need to be determined.

Culture of Detached Ears of Wheat in Liquid Culture: Modification and Extension of the Method

The method of culturing detached ears of wheat in a liquid medium has been modified to provide for the culture of ears from anthesis to maturity. For prolonged culture of ears, the presence of the peduncular node was beneficial. Grains developing in ears cultured from 2 days after anthesis until they had ripened germinated normally. By comparison with ammonium or nitrate, glutamine was the better source of nitrogen particularly at low levels of sucrose in the medium; inorganic forms of nitrogen inhibited grain-filling. Setting of grains was apparently dependent upon the availability of carbohydrate and there was no evidence from treatments involving shading for a photomorphogenetic response to reduced light intensity. While grain-filling was sustained by the provision of sucrose supplied artificially, light did nevertheless affect the accumulation of dry matter in the grains.

Recognition of Sand Body Depositional Environments: Limitations of Fourier Analysis and New Approach to Grain-Shape Analysis: ABSTRACT

In searching for subtle depositional traps, it would be useful to have a reliable method for determining the depositional environment of sand bodies from internal evidence. Attempts using various grain-size parameters have met with limited success. Recent advances in grain-shape analysis have not lived up to initial hopes. The potential of Fourier analysis is reduced when harmonic amplitudes are used without considering phase angles. Two types of errors can occur: (1) dissimilar shapes can produce similar sets of amplitudes, and (2) similar (but not identical) shapes can produce dissimilar sets of amplitudes. Phase angles can be compared between grains only when the grains are rotated to comparable positions; this can be accomplished by cross-correlation with an empirical asymmetric reference shape. Data reduction is desirable, but paired variables cannot be easily handled by standard multivariate techniques. After rotation to standard position, raw shape data (sets of radial lengths) are adequate shape descriptors. These can be reduced by factor analysis that can be compared between grains and between large sets of grains more meaningfully than can Fourier descriptors (which provide a poor basis for comparisons between grains). Results from the two approaches are compared in a preliminary re-study of the river-beach-dune discrimination problem. Gross grain shapes are classified into natural categories by multivariate analysis of rotated radials. End_Page 968------------------------------ Distinguishable associations of shape categories are quantitatively related to specific environments. Shape sorting, in combination with size sorting (different responses to transport processes), may extend the discriminating power. End_of_Article - Last_Page 969------------

Energetics of metamorphic crystallization

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.

Control of Sorghum Midge with Chlorpyrifos in Australia12

Chlorpyrifos and DDT were compared at different rates for control of Contarinia sorghicola (Coquillett) on grain sorghum in 3 replicated field experiments and 1 aerial field trial in New South Wales and Queensland in 1973 and 1974. With extended flowering of grain sorghum and 7 applications, chlorpyrifos at 150 g/ha at 5 day intervals gave significantly higher (P <0.05) yield in percent grain set than DDT at 500 g/ha at 5 day intervals. With restricted flowering and single applications chlorpyrifos at 280 g/ha gave significantly higher (P < 0.05) yield in set of grain than DDT at 1120 g/ha.

A theory of the tensile and compressive textures of face-centred cubic metals

The theory assumes that each grain in the aggregate undergoes the macroscopic strain. The possible rotations of a representative set of grains due to a small increment of strain are computed. It is found that in each grain a range of rotations can occur. A hypothesis is advanced to account for the different textures observed under similar straining conditions by metals of the same lattice. type. This is to the effect that the texture developed is determined by the relative hardening of active and latent glide systems. A further hypothesis enables the influence of specific types of hardening to be assessed. Diagrams compare observed and predicted textures.