Entire Grain Research Articles

A quantitative method of describing grain size distribution of soils and some examples for its applications

The grain size distribution of soils is known to be an important parameter in providing initial understanding for the physical and mechanical behavior of soils in many engineering geology applications. Therefore, the literature contains many grain size-based approaches, indices, or empirical models to describe soil for classification purposes or predict soil behavior under static and/or dynamic loading conditions. Because of the absence at present of a convenient single parameter that defines an entire grain size distribution curve, mean, median, standard deviation, the coefficients of uniformity and curvature, fines content, effective particle size etc., are currently used to describe the general slope and shape of the grain size distribution curve in engineering geological studies. In order to overcome with this limitation, comprehensive research has been performed in which an appropriate new parameter to represent grain size distribution curves is defined. Accordingly “grain size index (I GS)” is then used in a soil classification system and empirical models to predict physical and mechanical properties of soils. Statistical analyses were performed to prove its validity and to test its applicability for prediction of soil physical and mechanical properties. In addition to the availability of the I GS for soil classification and preliminary assessment of liquefaction properties of soil, it can also be used to estimate the swelling characteristics of expansive soils.

A new paradigm for star grain design and optimization

Purpose – The paper aims to extend the knowledge base for design and optimization of Star grain which is well known for its simplicity, reliability and efficiency. Star grain configuration is considered to be among the extensively used configurations for the past 60 years. The unexplored areas of treatment of ballistic constraints, non-neutral trace and freedom from use of generalized design equations and sensitivity analysis of optimum design point are treated in detail to bridge the gap. The foremost purpose is to expand the design domain by considering entire convex Star family under both neutral and non-neutral conditions. Design/methodology/approach – This research effort optimizes Star grain configuration for use in Solid Rocket Motors with ballistic objective function (effective total impulse) and parametric modelling of the entire convex Star grain family using solid modelling module. Internal ballistics calculations are performed using equilibrium pressure method. Optimization process consists of...

Experimental Investigation and Simulation of the Fatigue Mechanisms of a Duplex Stainless Steel under HCF and VHCF Loading Conditions

High frequency push-pull fatigue experiments on the austenitic-ferritic duplex stainless steel X2CrNiMoN22-5-3 (318LN) revealed that crack nucleation and crack propagation through the first grain determine significantly the lifetime of the material. Only in very few cases it was observed that fatigue samples which endured one billion load cycles without failure (run-out samples) contain microcracks which reached or overcame the first microstructural barrier (phase or grain boundary). This leads to the conclusion that in most cases the highest macroscopic stress or strain amplitude which does not lead to fatigue crack propagation through the entire first grain can be considered as the fatigue limit of the material. The present study documents that the experimentally identified fatigue mechanisms can be represented in mesoscopic finite element simulations by taking into account the effects of anisotropic elasticity, crystal plasticity, macro and micro residual stresses, plastic strain concentration in form of slip bands, crack nucleation and short crack propagation through the first grain. The current investigation shows that such simulations enable the determination of the fatigue limit of both real and synthetic microstructures. By means of real microstructures, containing slip traces and microcracks, the calculations can be verified and the required microstructural parameters can be determined.

How grain size controls friction and wear in nanocrystalline metals

Using molecular simulations we investigated the dependence of friction and wear on grain size in nanocrystalline copper. We found that effects of grain size are coupled to the effects of contact size, resulting in a transition from grain size--sensitive regime to grain size--insensitive regime in friction. This transition occurs because for small tips, friction-induced easy-shear planes can be entirely accommodated in a single grain, rendering grain boundaries less relevant to sliding resistance. Trends in friction do not follow trends in hardness, which is sensitive to grain diameter in the entire grain size regime considered in this study. We have also discovered that coupling of the effects of grain diameter and contact size leads to an optimum grain size that minimizes formation of wear chips on the surface.

Micromechanical properties of VT1-0 titanium cryorolled to various degrees of strain

Multipass rolling of VT1-0 titanium at a temperature near that of liquid nitrogen to a strain e = −2 resulted in grain refinement from ∼10 μm to ∼35 nm and a nearly twofold increase in microhardness. The microindentation measurements showed that the cryorolled samples had a rather homogeneous structure. An increase in the microhardness with increasing the strain can be described by the modified empirical Voce equation. The grain size dependence of the microhardness in the Hall–Petch coordinates consists of two parts with the slopes kHP1 and kHP2 < kHP1 for the grain size smaller than ∼250 nm. The strong temperature dependence of the microhardness for the investigated samples suggests that their plastic deformation has a thermally activated character. Close values of the thermoactivation parameters presumably indicate a common deformation mechanism in this material placed under an indenter over the entire grain size range.

Grain growth suppression in alumina via doping and two-step sintering

Efficiency of two-step sintering on grain growth elimination in the final stage of sintering of polycrystalline alumina has long been considered questionable. The published works failed either to suppress the grain growth entirely or to achieve the relative densities above 99% where the grain growth is the most severe. This paper reports on successful grain growth elimination in the final stage of sintering of a sub-micron alumina ceramics by a combination of the two-stage sintering and doping with metal oxides (MgO, ZrO2 or Y2O3). Relative densities up to 99.7% were achieved. Neither doping of aluminas sintered under conventional conditions nor the two-step sintering of pure alumina alone resulted in entire grain growth suppression in the final stage of sintering. A combination of the two-step heating regime with suitable doping (500ppm MgO added as MgAl2O4 nanopowder) led to complete grain growth suppression at relative densities above 99%.

Na2SO4·10H2O dehydration in view of thermal storage

The idea of using hydrated salts as working media for thermal energy storage has increased the interest in understanding their phase transitions. During studying the phase transition of mirabilite into thenardite, the crystal structure and water content are monitored by three experimental techniques. With the help of NMR, homogeneous drying of mirabilite crystals over the entire grain is observed. According to the drying behavior, the mobility of water molecules should be high inside the grain during dehydration. XRD experiments show that during this phase transition no disordered phase or other metastable phases like Na2SO4·7H2O or phase III appear. With Raman spectroscopy, these experiments are repeated at several relative humidities and again no metastable phases are observed.

Interaction between phase transformations and dislocations at the nanoscale. Part 2: Phase field simulation examples

The complete system of phase field equations for coupled martensitic phase transformations (PTs), dislocation evolution, and mechanics at large strains is presented. Finite element method (FEM) is utilized to solve this system for two important problems. The first one is related to the simulation of shear strain-induced PT at the evolving dislocation pile-ups in a nanosized bicrystal. Plasticity plays a dual part in the interaction with PT. Dislocation pile-ups produce strong stress tensor concentrators that lead to barrierless martensite (M) nucleation. On the other hand, plasticity in the transforming grain relaxes these stress concentrators suppressing PT. The final stationary M morphology is governed by the local thermodynamic equilibrium, either at the interfaces or in terms of stresses averaged over the martensitic region or the entire grain. This is very surprising because of strong heterogeneity of stress fields and is in contrast to previous statements that phase equilibrium conditions do not enter the description of strain-induced PTs. The second problem is devoted to martensitic plate propagation through a bicrystal during temperature-induced PT. For elastic growth (without dislocations) and a large thermal driving force, a complex transformation path with plate branching and direct and reverse PTs is observed, which still ends with the same stationary nanostructure as for a smaller driving force and a traditional transformation path. Sharp grain boundary arrests plate growth at a relatively small driving force, exhibiting an athermal friction. For elastoplastic growth, the generation of dislocations produces athermal friction and arrests the plate below some critical driving force, leading to a morphological transition from plate to lath M. The width of the martensitic plate increases in comparison with elastic growth due to internal stress relaxation. Plate growth is accompanied by the nucleation of dislocations within M and remaining in M, the nucleation of dislocations at the tip of a plate and spreading them in austenite (A), and passing some dislocations through M, then through a M-A interface, and then through A. Due to the existence of a stationary equilibrium M nanostructure and concentration for each temperature, for a large enough observation time one observes athermal, rate- and time-independent kinetics, even while local kinetics is rate dependent. In the final structure, most dislocations are in M despite its having a yield strength three times larger than for A, which is consistent with experiments.

IMPULSIVE SPOT HEATING AND THERMAL EXPLOSION OF INTERSTELLAR GRAINS REVISITED

The problem of impulsive heating of dust grains in cold, dense interstellar clouds is revisited theoretically, with the aim to better understand leading mechanisms of the explosive desorption of icy mantles. It is rigorously shown that if the heating of a reactive medium occurs within a sufficiently localized spot (e.g., heating of mantles by cosmic rays), then the subsequent thermal evolution is characterized by a single dimensionless number $\lambda$. This number identifies a bifurcation between two distinct regimes: When $\lambda$ exceeds a critical value (threshold), the heat equation exhibits the explosive solution, i.e., the thermal (chemical) explosion is triggered. Otherwise, thermal diffusion causes the deposited heat to spread over the entire grain -- this regime is commonly known as the whole-grain heating. The theory allows us to find a critical combination of the physical parameters that govern the explosion of icy mantles due to impulsive spot heating. In particular, the calculations suggest that heavy cosmic ray species (e.g., iron ions) colliding with dust are able to trigger the explosion. Based on the recently calculated local cosmic-ray spectra, the expected rate of the explosive desorption is estimated. The efficiency of the desorption, which affects all solid species independent of their binding energy, is shown to be comparable with other cosmic-ray desorption mechanisms typically considered in the literature. Also, the theory allows us to estimate maximum abundances of reactive species that may be stored in the mantles, which provides important constraints on available astrochemical models.

Preferred orientation of grain boundary plane in recrystallized high purity aluminum

Compared with the research of preferred orientation of crystals (crystallographic texture) which started nearly a century ago, preferred orientation of grain boundary plane in polycrystalline materials is a lately proposed research direction with the development of five parameter analysis which is based on electron backscatter diffraction and stereological method. Systematic investigations into the preferred orientation of grain boundary plane and in-depth understanding on their evolution natures will be important to the manipulation of the microstructures of desired properties. In current paper, high purity aluminum (99.99 wt%) samples were cold rolled with 85% thickness reduction followed by a recrystallization annealing at 330℃ for 15-60 minutes and then the grain boundary plane orientations were studied. The results indicate there indeed exist preferred orientations of grain boundary planes in the recrystallized microstructure and the preferred orientation evolves sequentially from {2 2 3} to {1 1 1} and {1 0 0} planes during grain growth. Further discussion points out the recrystallization of high purity aluminum after cold rolling could be a so-called continuous recrystallization which involves sub-grain coalescence and sub-grain growing, and low angle grain boundary (mis- orientation angles ranging from 2° to 15°) constitutes the main part of the entire grain boundaries in the recrystallized microstructure. During grain growth, the crystallographic texture evolves from {1 1 0}<1 1 2> (Brass) to {0 1 1}<1 0 0> (Goss) and {0 2 3}<1 0 0>co- existed, and low angle grain boundary planes usually orient on the exact position of low energy tilt boundaries due to the effects of crystallographic texture and crystallographic plane energy. This is the reason for the regular evolution of the preferred orientation of grain boundary planes as observed.

SIMULATION OF A MATHEMATICAL MODEL FOR THE TEMPERATURE PROFILE IN A SILO BAG FOR BEAN

The problems encountered with storage of agricultural products has warranted studies related to finding alternative methods of grain storage, thereby avoiding unnecessary losses. Stored grain deteriorates quickly at high temperatures. The moisture content of the grain influences the respiratory process; therefore, when at the recommended humidity of between 11 and 13%, this rate remains low, it prolongs maintenance of the product quality. The silo bag being airtight enables the grain mass to consume the entire internal O 2 purse within it, and in that low or absent oxygen environment the grain mass saturates the CO 2 atmosphere, inhibiting the multiplication of insects and fungi, thus providing a controlled environment. This study aims at simulating, using Computational Fluid Dynamics (CFD), the time it would take for the entire grain mass contained in a silo bag to reach thermal equilibrium with the environment and analyzes the feasibility of the technique employed here. The simulations were performed based on the data of the average air temperature in the region at each harvest time and the average storage temperature of the bean mass (60°C). The results obtained from the simulations reveal that after one month of silo storage the entire bag remains in thermal stabilization, and four months later when it hits the entire mass, all the beans are in thermal equilibrium. Therefore, maintaining stable temperature and humidity within the recommended silo bag preserves the grain quality well.

Effects of different milling processes on whole wheat flour quality and performance in steamed bread making

In recent years there has been growing interest in whole grain products. However, few studies have analyzed the influence of whole wheat flour on the quality of Chinese steamed bread. This study determined the influence of different milling processes on the physicochemical properties and steamed bread quality of whole wheat flour. A medium hard red wheat, soft white wheat and Canada hard wheat was used as raw materials. The milling processes including three entire grain grinding and four bran recombining processes. The wheat flour ground by roller mill was used as a control. Results showed that whole wheat flour made from entire grain grinding processes had higher viscosity values but lower particle size than bran recombining processes. Appropriate processes can improve the farinograph characteristics of whole wheat flour. Chinese steamed bread of whole wheat flour obtained from bran recombining had larger height/diameter ratio, specific volume than that from entire grain grinding processes. Ultrafine entire grain grinding process especially when using white wheat improved the color of steamed bread. The texture differences of steamed bread between whole wheat flour and flour were significant. Steamed bread of red wheat from heat-treated bran recombining (HTBR) process got the highest sensory score.

M23C6 precipitation behavior and grain boundary serration in Ni-based Alloy 690

A study on the Cr-rich M23C6 precipitation and grain boundary serration in Ni-based Alloy 690 was conducted through various heat treatments. Fine granular carbides and discontinuous precipitates were evolved during isothermal treatments at 720°C for 0.1–100h, and their precipitation morphologies and behaviors were considerably varied depending on the grain boundary characteristic. Carbide precipitation was retarded on the low angle grain boundaries, compared to that on the random high angle grain boundaries. Needle-like carbides were precipitated on the incoherent twin boundaries. The discontinuous precipitates were initiated even by a heat treatment of 0.1h, and covered the entire grain boundary region within a heat treatment of 10h. Grain boundaries were serrated by a slow cooling process, and it was revealed that the serration occurred in a limited temperature range during controlled cooling. As the average grain size with more carbon content increased and/or the cooling rate decreased, the degree of serration increased with a precipitation of coarse planar intergranular M23C6 carbides. The grain boundaries had a convex shape into the incoherent grain. It is suggested that the grain boundary migration during serration is closely correlated with the precipitation of intergranular Cr carbides in this alloy.

Grain shape effect on the anisotropic behaviour of silt–sand mixtures

The anisotropy of sand–silt mixtures has not been fully studied in terms of the effects of different grain shapes and silt content. This study investigated the effects on anisotropy in three different sands with various silt contents and grain shapes. The tests performed in this research include 90 hollow cylinder torsion shear tests conducted on three types of sand: Hamadan sand with high angularity, Firoozkuh sand with medium angularity and Tehran sand with low angularity. The samples had silt contents of 0, 15, 30 and 50 per cent. To define the shape criteria in this study, two ratios were defined. The first was roundness, which can be obtained from the ratio of the radius of the corners of the grains to the largest circle that encompasses the entire grain; this ratio is denoted by rr. The second criterion was sphericity, which can be obtained by dividing the smallest pictorial width by the minimum graphical length; this ratio is denoted by rs. Under similar initial effective confining pressures, sand with high roundness and sphericity showed contractive behaviours. An increase in silt content, as well as in the ratios rr and rs, decreased the sample strength. Moreover, increasing these two ratios caused the stress–strain curves to be close to one another.

Selenium uptake, dynamic changes in selenium content and its influence on photosynthesis and chlorophyll fluorescence in rice (Oryza sativa L.)

Approximately two-thirds of the cultivated soil in China is Selenium (Se)-deficient, which often results in a lack of Se in the human population of this region. Therefore, developing an effective method to increase the Se content in crops has become a considerable effort. In this study, the uptake and distribution of Se, the dynamic changes in Se content, and the effects of different concentrations of Se on grain yield, photosynthetic parameters and chlorophyll fluorescence parameters (0–100g Seha−1) were measured in field experiments to clarify the response of rice crops to Se and the relationship between Se and the photosynthetic system. The results revealed that the grain yield was increased due to application of Se, peaking in areas treated with 50g Seha−1. The Se content in various parts of the rice plants significantly increased as the Se level increased. Furthermore, the Se content in each part of the rice plants decreased from the roots to the shoots to the grains, and the Se content in the shoots and the roots after Se treatment decreased from the tillering stage to the mature stage. However, little change in the grain Se content was detected throughout the entire grain growth phase. Furthermore, the application of Se enhanced photosynthesis by increasing the photosynthesis rate (Pn), the intercellular CO2 concentration (Ci) and the transpiration efficiency (E) of rice. Se treatment enhanced the activity of the photosynthetic system by increasing Fv, Fm, Fv/Fm and Fv/Fo and decreasing Fo. The present study suggests that the changes in both the photosynthetic system and the grain Se content were closely associated with the application of Se and that an increased Se concentration in rice could induce photosynthesis, thereby increasing the grain yield of rice. The photosynthetic or chlorophyll fluorescence parameters could be used to determine the sufficiency of Se treatment during the production of Se-rich rice.

U-Pb geochronology of the type Nazas Formation and superjacent strata, northeastern Durango, Mexico: Implications of a Jurassic age for continental-arc magmatism in north-central Mexico

U-Pb ages of ignimbrites and detrital-zircon analyses from Middle Jurassic through lowermost Cretaceous strata in northeastern Durango, Mexico, indicate the age of local volcanism and the age range, respectively, of the Jurassic continental-margin arc in north-central Mexico, where it is termed the Nazas arc. The type Nazas Formation along the Rio Nazas consists of red continental sandstone and siltstone, ignimbrites, and intermediate flows that provide an important record of the extensional Jurassic Nazas magmatic arc. Overlying shallow-marine sandstone and shale of Late Jurassic to earliest Cretaceous age represent deposits of younger extensional basins that are part of the Border rift system, which extended from southern Arizona to the Gulf of Mexico. The younger strata constitute volcanic litharenite and lithic arkose derived from the Jurassic volcanic rocks and from basement rocks of the Coahuila block to the north. Two ignimbrites in the upper part of the Nazas Formation have statistically indistinguishable ages of 170 ± 2 and 169 ± 2 Ma. The ages are consistent with their stratigraphic order and position above volcanic-lithic sandstone with a maximum depositional age of ca. 180–178 Ma calculated from detrital zircons. Six detrital-zircon age populations were defined from four sandstone samples ( n = 377 zircon grains) of the Nazas Formation and overlying La Casita and Carbonera Formations. The most prominent age clusters (≥10% of the entire grain population) have ranges ca. 1277–890 Ma (Grenville, 22% of total), ca. 486–310 Ma (early Paleozoic, 11%), and ca. 202–159 Ma (Jurassic, two populations constituting 54% of total grains). The Jurassic age cluster indicates that Nazas arc magmatism in the region took place during the Early and Middle Jurassic and ended by early Late Jurassic time. The Nazas Formation correlates with arc-related Middle Jurassic strata in Sonora, southern Arizona, and southeastern California that contain interbedded eolian sandstone derived from the Jurassic ergs of the Colorado Plateau; absence of interbedded eolianite in the Nazas Formation thus indicates that the outcrops of north-central Mexico were likely not translated to their present locations along a regional, Late Jurassic transcurrent fault system, as postulated by some workers. Detrital-zircon data from the Upper Jurassic and lowermost Cretaceous strata indicate that Jurassic volcanic rocks covered the Coahuila block, directly north of the study area, at the end of Middle Jurassic time. Sandstone composition and detrital-zircon ages record erosional unroofing of the Coahuila block, whereby removal of Lower and Middle Jurassic volcanic and volcaniclastic strata exposed Grenville, Pan-African, and peri-Gondwanan basement of the block during Late Jurassic time.

Variation of strain rate sensitivity with grain size in Cr and other body-centred cubic metals

The strain rate sensitivity (i.e. m-value) of body-centred cubic Cr was measured over a wide grain size range (10−9–10−2 m) using an instrumented nanoindentation technique. The m-value was observed to decrease initially as the grain size was reduced from mm to µm, it reached a minimum, and then increased drastically when the grain size was below 20–30 nm. There was a corresponding variation in activation volume, particularly when the grain size was in the nm range and the grain-boundary-mediated process became dominant. The variation of m-value and activation volume over the entire grain size range could be rationalized by a model based on a double-kink mechanism coupled with the dislocation emission processes from the grain boundaries.

Measurement of distributions of cesium and rubidium in rice grains using micro-PIXE for detailed examinations of contaminated food

We used micro-PIXE to investigate the distribution of Cs and Rb in rice grains. We succeeded, for the first time, in measuring the elemental distributions in entire rice grains (with dimensions of 6.25 mm [Formula: see text] 6.25 mm) at micrometer spatial resolution. We found that Cs and Rb accumulated in the bran and germ of the rice. The distributions of P, K, Rb and Cs were similar within the rice grain. The concentrations of Cs and Rb in the rice were proportional to those in the soil, as well as to the exposure time. The uptake of Rb was significantly larger than that of Cs. Furthermore, the behavior of Rb was similar to that of Cs in the micrometer-scale regions in plants. It follows that the distribution of Rb can be used to investigate the behavior of radioactive Cs in plants.

A novel superplastic mechanism-based constitutive equation and its application in an ultralight two-phase hypereutectic Mg–8.42Li alloy

A superplasticity mechanism based constitutive equation incorporating deformation-induced grain growth and deformation-accelerated grain boundary diffusion was established. The constitutive equation established was applied to the superplastic two-phase hypereutectic Mg–8.42Li alloy. The contribution of net static grain growth to entire grain growth accounts for 51.65% while the contribution of net strain grain growth to entire grain growth accounts for 48.35%. It is shown by calculation that the grain boundary diffusion in the superplastic deformation of fine grained microduplex Mg–8.42Li alloy at low strain rates is not accelerated obviously and deformation-accelerated grain boundary diffusion takes place at high strain rates. It is indicated by normalizing the data of calculation and experiment that the flow mechanism of this alloy at 573K at an initial strain rate of 5×10−4s−1 is modified Mukherjee's grain boundary sliding controlled by the motion of the dislocations in the grain boundaries by a climb-glide process and Gifkins's grain boundary sliding occurring by the motion of grain-boundary dislocations that pile up at triple point.

Evaluación de cultivares de arroz (Oryza sativa L.) bajo condiciones de secano y riego. Panamá. 2002-2003.

Se evaluo la estabilidad (AMMI y el Biplot GGESREG) yotras caracteristicas de 20 genotipos de arroz, en secano y riego.Para el sistema de secano, hubo diferencias en rendimiento,sobresaliendo FLAR 54-00, IDIAP 38 y Lajas 02-00. Encalidad de grano, el rendimiento total vario entre 61,8 a68,0%, los granos enteros entre 43,6 y 56,5%, y el centroblanco vario entre 1,5 y 3,4. Para la digestion alcalina, diezgenotipos mostraron grados de dispersion entre seis y sietecon baja temperatura de gelatinizacion, ocho con grado decuatro a cinco considerados intermedios. El FLAR 54-00 respondiomejor a los estimulos ambientales. Prosequisa, CHI32-10 y CHI 45-23, presentaron el comportamiento mas pobreen la mayoria de ambientes. El modelo Biplot GGESREG,identifico como genotipos estables, al FLAR 54-00, FLAR198-00 y Fedearroz 50. Para el sistema de riego, hubo diferenciasen rendimiento, destacandose IDIAP 38, P-3621 y Fedearroz50. La calidad de granos, mostro rendimiento totalentre 65,8 a 70,9%, granos enteros entre 51,5 y 62,0%, la incidenciade centro blanco vario entre 1,2 y 2,8. En digestionalcalina, nueve genotipos presentaron grados de seis y siete,y diez genotipos con grados de cuatro a cinco. IDIAP 38, P-3621 y FLAR 54-00, respondieron mejor a los estimulos ambientales.Prosequisa, FLAR 195-00, CHI 49-16 y CHI 13-256, presentaron el comportamiento mas pobre. Losgenotipos mas estables bajo riego, fueron Fedearroz 50,IDIAP 38 y P-3621.