Interlocking Of Grains Research Articles

Microstructures and Toughening Mechanisms of Y<sub>2</sub>O<sub>3</sub> Doped Al<sub>2</sub>O<sub>3</sub>/ZrO<sub>2</sub> Eutectic Composite Ceramics Prepared by SHS Melt-Growth Process

By introducing ZrO2(4Y) powder of suitable content into the thermit and based on oxidation-reduction reaction of the thermit and liquid-liquid phase separation of ceramics/metal under gravity, Al2O3/ZrO2(4Y) composite ceramics have been prepared through melt-growth with eutectic reaction under high degree of undercooling from SHS process. It has been found that the ceramics were composed of major rod-shaped sapphires with 8.0~12.0 aspect ratios and minor plate-like α-Al2O3 grains, and within the sapphires t-ZrO2 nano-micron fibers were embedded. Flexural strength and fracture toughness were measured to be 1256MPa and 13.2MPa·m1/2. It was obtained that a number of low energy interfaces (the interface distance on nano-micron scale) between two Al2O3/ZrO2 (4Y) phases and the strong compressive residual stress in the sapphires made the sapphires reinforced, forcing the crack to propagate along the rod-shaped sapphires; meanwhile, crack-bridging and pull-out of the sapphires, crack - bridging and frictionally interlocked effects of plate-like α-Al2O3 grains in the wake of crack tip also rendered the crack stabilization to arise.

Influence of accessory substances, wood density and interlocked grain on the compressive properties of hardwoods

Wood samples of nine tropical hardwoods from Peru and sugar maple wood from Quebec were selected to perform moisture sorption tests associated with parallel-to-grain and tangential compression tests using a multiple step procedure at 25°C. Cold-water and hot-water extractives, sequential cyclohexane (CYC), acetone (ACE) and methanol (MET) extracts, ash content (ASH), wood density and interlocked grain (IG) were evaluated on matched samples too. Wood density corrected for the accessory substances was by far the major factor positively affecting the compressive properties of tropical hardwoods. The total amount of accessory substances is required in order to establish better relationships between physico–mechanical properties and density of tropical hardwoods. For a given wood density, the ultimate stress in parallel-to-grain compression was higher in tropical hardwoods than in temperate hardwoods. However, the compliance coefficients for both types of woods were quite similar. Sequential extraction with organic solvents was the most suitable method for evaluating the effect of extractives on compressive properties of tropical hardwoods. The CYC and ACE fractions did not contribute to variation in these mechanical properties. The substances dissolved in MET affected positively the compliance coefficient s11 in parallel-to-grain compression and negatively the compliance coefficient s33 in tangential compression. The IG decreased the compliance coefficient s11 but also decreased the ultimate stress in parallel-to-grain compression. Finally, variations in compressive properties that were due to changes in equilibrium moisture content (EMC) were clearly influenced by wood density; denser woods were more sensitive to changes in EMC than lighter woods.

Physical properties of Titan's surface at the Huygens landing site from the Surface Science Package Acoustic Properties sensor (API-S)

We present the results from the first sonar to be deployed outside of Earth, and the first active acoustic instrument on Titan, onboard the Huygens probe, and the implications of its data for the geomorphology and characteristics of the Huygens landing site. Signals were recorded from 90 m downwards until impact, with a maximum sensor footprint diameter at the ground of 39.2 m. Probe impact speed was measured to be 4.67 m s −1. Derivation of terrain topography in a transect beneath the probe may indicate a ridge-trough terrain with an amplitude of about 1 m and a wavelength of about 10 m, although a flat surface is also consistent with the results. Modelling of the returned signal indicates that the surface acoustic properties at the landing site must be specular in nature, which may have two possible (not incompatible) causes—the surface may consist of sorted interlocking grains, smooth on the centimetre scale, which would imply either fluvial sorting or the infill of small particles interstitial to the larger particles (similar to a terrestrial playa). Alternatively, specularity may indicate the presence of methane as an interstitial liquid or as very small pools. Due to mission constraints, tens of metres around the landing site were not well-imaged by Huygens' cameras except for the narrow azimuth observed after impact (the camera did not look straight down, and was not in imaging mode during the last few hundred metres of descent). Thus the data presented are among the few direct observations of the landing site surroundings.

The effect of planting density on the wood quality of South African-grownEucalyptus grandis

This paper presents the results of a wood property and sawn board quality study performed on disc samples and sawlogs taken from a 23-year-old Eucalyptus grandis Nelder 1a spacing trial at J.D.M. Keet plantation near Tzaneen. Ten trees from each of four markedly different planting densities were chosen to provide contrasting material to study the effects of growth rate on the quality of the wood produced. Spacing treatment diameter means ranged from 18.9 to 57.9 cm. An inverse relationship was found between planting density and wood density. Typical pith-to-bark density profiles for trees at this age occurred in the trees with rapid growth, i.e. steep gradients from the pith towards the bark during the early stages of growth, followed by a gradual transition into more constant mature wood density values. Trees of which the growth had been curbed by higher planting densities, on the other hand, showed little sign of levelling off. As a result, the faster growing trees contained significantly larger proportions of relatively homogeneous wood compared to the slower grown trees, giving them an obvious quality advantage over slower grown trees. Accelerated growth thus seems to yield trees that can be utilized more effectively and converted into products with more reliable performance characteristics. Fast growth seemed to promote interlocking grain, but the correlation with interlocking grain severity was too poor to be of any practical significance. Mean splitting showed a downward trend with decreasing planting density, but statistically the differences were non-significant. A statistically significant correlation was found between the amount of splitting in logs and the proportional length of sawn boards affected by splits immediately after wet-mill processing. At the end of the sawmilling process, however, such correlation did not exist any longer, suggesting that the boards responded differently to drying stresses and impacts during handling and transport with regard to further splitting. No significant effect of planting density on sawn volume losses due to splitting or collapse could be detected.

Machining Cracks in Finished Ceramics

Grinding may create flaws that control strength and limit the performance of finished ceramics. Machining cracks sometimes have been difficult or impossible to find especially in toughened ceramics with interlocking grain microstructures that create rough fracture surfaces. Our fractographic examinations show that machining damage leaves telltale markings on fracture surfaces that may be easily detected using common fractographic techniques. A comprehensive study with over 400 ground rods and rectangular bars was conducted on several commercial silicon nitrides to study the effects of various machining conditions. Similarities and differences in behavior were observed. A paradoxical finding was that tougher silicon nitrides developed deeper grinding cracks. Machining crack size and shape strongly depended on the grinding wheel grit size.

New anatomical method of grain angles measurement using confocal microscopy and image cross-correlation

Some tropical trees with indistinct growth rings have a distinct interlocked grain that reveals their internal growth rhythm. To determine their growth rhythm, it is necessary to accurately measure the wood grain angle. The usual methods for grain angle measurement are radial splitting using wood disks, which occasionally provides inaccurate data, and serial tangential sectioning, which requires preparation and analysis of many sections. The present report proposes an easier but accurate method to measure grain angle using a single xylem transverse section. A confocal microscope was used to obtain two optical sections of different depths from a transverse section of a 7-year-old Hopea odorata Roxb. The tangential lag between the optical images was then calculated using image cross-correlation and transformed into grain angle. Radially consecutive sampling revealed distinct radial fluctuations in the grain angle. The fluctuation data were compared to data obtained by radial splitting and serial tangential sectioning. There was a strong correlation between grain angle using the three methods. In the region close to the cambium, however, the present method revealed an abrupt change in the grain angle, although radial splitting showed a smooth undulation throughout the radius. Using the present method, the analysis of a radial range of 5 cm required a single transverse section compared to 1,000 tangential sections 50-μm thick. In conclusion, the present method using a single transverse section, confocal microscopy, and image cross-correlation analysis provides more accurate data than radial splitting, and is less time-consuming than serial tangential sectioning.

Relationships between texture and mechanical properties of hybrid rocks from the Jaala–Iitti complex, southeastern Finland

The relationships between petrographical and mechanical properties of rock aggregate raw materials from the hybridised, subvolcanic Jaala–Iitti complex, southeastern Finland, were investigated. Petrography was quantified from polished thin sections with a polarising microscope to determine the modal composition and grain size distribution, and resistance to fragmentation and abrasion were determined. Abundance of fine-grained minerals (especially of hornblende), fine grain size-dominated grain size distribution, uniform spatial dispersion of hornblende crystals, and intense micrographic intergrowth texture with interlocking grain boundaries were found to have the greatest positive influence on the mechanical properties. The results showed the potentiality of hybridised rocks as raw materials for high quality aggregates that can resist fragmentation and abrasion.

Rearrangement of cells in storeyed cambium of Lonchocarpus sericeus (Poir.) DC connected with formation of interlocked grain in the xylem

The history of cellular events in the storeyed cambium of Lonchocarpus sericeus (Poir.) DC was analysed on the basis of changes in the cell arrangement in successive layers and strata of axial parenchyma in the xylem. The mechanism of formation of the regular interlocked grain was investigated. Inclination of fusiform cells changes intensively whereas height and position of storeys in the successive layers of axial parenchyma are constant. As a result, new contacts between cells are formed by means of the intrusive growth of ends of cells belonging to one storey between the tangential walls of cells of the neighbouring storey and unequal periclinal divisions, which give a new shape to the initials. The concept of intrusive growth between the radial walls of the fusiform initials in the formation of xylem with interlocked grain should be revised on this basis.

MACROSCOPIC AND ANATOMICAL INVESTIGATION OF INTERLOCKED GRAIN IN ACACIA MANGIUM

Interlocked grains record change in the orientation of axial elements. In this report, vessel and fiber orientations in Acacia mangium Willd. were compared macroscopically and microscopically to analyze the interlocked grain. A method to print the cylindrical surface of a dry wood disk after bark exfoliation was devised to evaluate the stem axis and circumferential grain fluctuation and revealed circumferential heterogeneity in the vessel orientation. Fiber orientation manifested on some radial splits also was heterogeneous. A 3 mm-thick transverse plate was used to estimate vessel orientation with soft X-ray photography, which enables a wider-ranging evaluation than microscopy. Serial tangential thin plates and sections were used to measure fiber orientation angle with reflecting and polarized light microscopy, respectively, and fast Fourier transform. Both vessel and fiber orientations had a similar radial tendency and distinct inversion of the grain. However, the vessel orientation had a larger amplitude of change than fiber orientation.

Fracture Energy of an Aligned Porous Silicon Nitride

The fracture energy of a porous silicon nitride with aligned fibrous grains was investigated, using a chevron‐notched‐beam technique. A crack was constrained to propagate normal to the grain alignment. The obtained fracture energy was ∼500 J/m2, which was ∼7 times larger than that of a dense silicon nitride with randomly oriented fibrous grains. The large fracture energy was attributable primarily to the sliding resistance associated with interlocking grains.

Some geotechnical properties of the Claygate ‘Beds’ and Bagshot ‘Beds’ of south Essex

Abstract The Claygate Beds and Bagshot Beds are the uppermost formations of Eocene age in south Essex, the former resting on the London Clay. The Claygate Beds consist primarily of silts and clays with subordinate sands, whilst sands are more common in the Bagshot Beds. The paper describes the geotechnical properties of these two sedimentary units. The results form part of a larger study of the engineering geology of south Essex. The sands, particularly in the Bagshot Beds, are fine grained. All the sands are uniformly sorted and negatively skewed. Quartz is the principal minerals in these beds and in the fine material, mica, montmorillonite, kaolinite and chlorite figure in that order of relative abundance. The geotechnical properties of the silts and clays of both formations are generally similar. However, the plasticity of the Claygate Beds tends to decrease somewhat from the lower to the upper division and the range of plasticity is greatest in the upper division. This may be due to the greater variation in quartz content and montmorillonite content in the latter division than in the two others. The clays in both formations tend to have normal activity whilst that of the silts is both normal and active. The values of the undrained shear strength parameters, especially in the sandy material, are influenced by the amount of cement present, and the degree of interlocking of grains and the degree of compaction. The undrained shear strength of the silts and clays suggests that they range from soft to very stiff.

焼結タングステン細線の高温クリープに及ぼす2次再結晶粒形態の影響

It is investigated how the morphological change of secondary recrystallized grains grown in powder metallurgy tungsten fine wires has an effect on creep at high temperatures after it is quantitatively estimated. The quantitative treatment of the grain morphology is possible by using f1 as the representative one of the grain shape parameters. The optimum interlocked grain structure is defined as the grain morphology in which the grain aspect ratio is minimized under the condition that the area of grain boundaries does not increase drastically. The high-temperature creep can then be characterized by the index ΔI(=f1−f10) which indicates the degree of deviation from the optimum interlocking of grains which is designated by f10. The region of power law creep in the deformation mechanism maps is minimized at ΔI=0 at which the grains are most favourably interlocked, being extended as ΔI deviates from ΔI=0. It is considered that the deformation in the region is strongly influenced by grain boundary sliding, being further done by grain boundary cavitation with an increase in ΔI at ΔI>0.

Grain-shape parameters for high-temperature creep resistance in powder metallurgy tungsten fine wires

Three grain-shape parameters, f{sub 1}, f{sub 2}, and f{sub 3}, are defined to clarify the morphological effect of grains on the high-temperature creep resistance under the condition that no grain boundary cavitation occurs. The parameter f{sub 1} is characteristic of complicated grain shapes, suggesting that it can be a measure of the interlocking grain structure. The parameter f{sub 2} is an important parameter when torsional stresses are imposed on coiled wires, and f{sub 3} is characteristic of the short-range roughness of grain boundaries only when f{sub 1} is not greatly changed. The minimum creep rate decreases as the grain aspect ratio, R, increases for R 30. The parameter f{sub 1}, as well as Raj and Ashby`s model, gives a satisfactory explanation for the former behavior. On the other hand, it is proven that their model must be modified using f{sub 3} to explain the latter behavior because of the highly elongated grain configuration that is associated with R > 30.

木質材料 スパイラルワインディング法を用いて製造した円筒形ＬＶＬの製造条件と機械的性質

The mechanical properties in bending and in compression of full size cylindrically laminated veneer lumbers (C-LVL) made by spiral winding method were tested. The C-LVLs have about 300mm outer diameter, 25mm wall thickness, and 3600mm length. The results obtained are as follows: 1) The modulus of elasticity (MOE) of C-LVL depends on the species of veneer raw materials, that is, MOE of C-LVL was the same as the MOE of solid lumber of the same species. 2) The number of plies affects the modulus of rupture (MOR) and the mode of failure of C-LVL. It has no effect on MOE. 3) The interlocked grain structure of C-LVL with ±10 degree in alternate layers effectively prevented decrease in MOE of C-LVL compared to that of solid lumber. 4) There was little effect on MOE or MOR by the addition of radial filler in C-LVL with 10 plies or more. 5) The properties in compression is about equal to those in bending. In the compression test, buckling failure was observed. These results show that C-LVL is suitable for structural uses, especially as building and construction posts.

Minimum Surface Formation Energy for Three-Dimensional Intergranular Fracture

AbstractThe minimum expended energy for fracture is the free energy required to form two new surfaces. For intergranular fracture, the minimum surface formation energy is complicated by the rough fracture surface, with area greater than the specimen cross-section. We utilize network optimization algorithms (max-flow/min-cut) to determine the minimum surface formation energies and surfaces for intergranular fracture in 3D polycrystals. For equiaxed grains and uniform boundary strength, the minimum energy fracture area is independent of grain size and is 45% larger than the specimen cross-section, and intergranular fracture will occur when surface energy is less than 1.6 times the grain boundary energy. The 3D fracture area is larger than projected from 2D systems. In systems with microcracked boundaries, the fracture surface deviates to preferentially include microcracked boundaries, creating interlocking grain configurations. Two-dimensional percolation of microcracks occurs at about 80% microcracked boundaries.

焼結タングステン細線の異常結晶粒成長に及ぼすバブルの影響に関する計算機実験

The shape of abnormal grains has a decisive effect on the grain boundary fracture at room temperature and the characteristics of creep at high temperatures in P/M tungsten fine wires. The effects of the amounts and distributions of bubbles in a material on it are therefore investigated using a Monte Carlo computer simulation technique. The abnormal grain growth initiating from the surface of a specimen can be simulated with a more dense distribution of the nuclei for abnormal grains near the surface, giving the microstructural time evolution similar to the structural change in a wire. The microstructure obtained presents several features as follows: (1) Some of abnormal grains with the nuclei of large size tend to survive after the others vanish during their growth. (2) A largest abnormal grain existing up to the final stage increases its size as the number of the nuclei for abnormal grains decreases. (3) The abnormal grain growth is accelerated when the primary one is strongly inhibited by the pinning force due to bubbles. It can be concluded from these results that the interlocking grain structure results mainly from the shape of the grains which is produced when the abnormal grains break away from an array of bubbles in various ways.

Quantitative analysis of closure stress-crack separation curve in grain bridge toughening of polycrystalline ceramics

Finite element analysis has been applied for a quantitative understanding of the crack closure stress-separation function due to the grain-bridging mechanism in polycrystalline ceramics. The grain-bridging process of a two-dimensional planar array model was analysed and the crack closure stress during crack bridging under a single-bridging condition was obtained as a function of the crack separation. The effects of grain size, Young's modulus and coefficient of friction for interfacial sliding on the crack closure stress were obtained numerically. The results showed that the grain-bridging process was made up of three characteristic stages. The major contribution to grain bridge toughening is interlocking of grains that operate at the first stage. The crack closure stress at the same crack separation tended to increase with increasing Young's modulus and decreasing grin size respectively.

Ind

The study describes moulding recovery and quality of seven Indonesian industrial wood species, i,e. meranti putih (shorea koordersii), sungkai (phenomena canescens jack). Cempaka (elmerillia ovalis dandy), dahu (dracontomelon dao), perupuk (solenospermum sp.) meranti merah (shorea sp.). and kapur (dryobalanops sp.). It is found that volume recovery varies from 38.7 to 80.2 per cent. An optimal allowances for moulding raw material are 3.0 mm in thickness and 9.6 mm in yidth Sungkai, dahu, perupuk and kapur species produced the best moulding quality. Moulding quality of the other species is found to be of good quality. The processing of cempaka and meranti species, especially on their radial surface or quarter swan timber, should be undertaken carefully because of they have genetical interlocked grains.

Potassium bubbles in tungsten wire

Tungsten filaments for incandescent lamps almost always contain potassium bubbles. These are required to produce the interlocking grain structure that gives the tungsten lamp filament a long life. In this article, we consider the formation of the bubbles from the ellipsoids of potassium produced by deformation, the growth of these bubbles as a result of internal pressure created by the potassium vapor within the bubbles, and the reasons why these bubbles can sometimes grow to very large sizes. In each case, we present a simple model to describe the process. We finally use nucleation theory to describe the overall process of bubble growth.

Interlocked grain growth of YBCO film on magnesium oxide as observed by scanning tunneling microscopy

Thin films of YBa 2Cu 3O 7 on MgO deposited by RF magnetron sputtering to study their superconducting behavior, were examined by a Scanning Tunneling Microscope. The films were deposited at room temperature, sintered exsitu at 850°C, 900°C, 930°C,950°C and 980°C for 30 minutes each and cooled at rate of 100°C per hour in oxygen ambient. Topographic images taken in air show that the films which were initially amorphous in nature, gradually transform to a layered grain structure with the increase of sintering temperature. Films sintered at temperatures above 900°C are c-axis oriented and have a coarse grain structure. These grains are connected mutually by a well defined interlock, formed between the layers of neighboring grains. The mechanism of interlocking of layers from adjacent grains and its possible influence on the superconducting properties has been discussed.