Papers by Keyword: Grain Size Distribution

Abstract: Spatial distribution of microalloy precipitates have been characterized in a low carbon microalloyed steel containing Nb, Ti and V. Micro-segregation during casting resulted in an inhomogeneous distribution of Nb (and also Ti) precipitates in the as-cast slab. Austenite grain growth has been investigated in the above mentioned steel, using different reheating temperatures between 1000°C and 1250°C for 1 h. Inhomogeneous distribution of Nb-rich precipitates created austenite grain size bimodality after reheating to an intermediate temperature range (1150-1200°C). Uniformly fine and uniformly coarse grain structures were found after reheating at lower- (≤ 1075°C) and higher-reheating temperatures (≥ 1250°C). A model has been proposed for the prediction of austenite grain size variation in the reheated steel.

Abstract: Tailing sand from ex-tin mine in Batu Gajah containing between 95.9 to 98.9% silica. In this research involved the process of, conducting the mechanical sieve grading to identify the size spread, plotting the grain size distribution and calculating the average grain size. Further on with the effects of controlled additions of clay (bentonite) and water and determining the working range on the mechanical properties. The investigation involved comparing the mechanical properties of the tailing sand to the requirement for foundry sand applications listed by Foseco Ferrous Foundrymans Handbook (Foseco). Permeability and green compression strength are the important mechanical properties and considered much in the sand casting mould preparation. These mechanical properties play a vital role in determining the allowable clay and moisture content for working range of tailing sand for making green sand casting mould. Experiments for this investigation were conducted according to American Foundrymen Society (AFS) standard of procedures. Cylindrical test pieces dimensioning of Ø50 mm×50 mm in height from various sandwater ratios bonded with 3.8%wt clay and then 7.4%wt clay, were compacted by applying three ramming blows of 6666 g each using Ridsdale-Dietert metric standard rammer. The specimens were tested for green compression strength using Ridsdale-Dietert universal sand strength machine and permeability number with Ridsdale-Dietert permeability meter. Before the tests were conducted, the moisture content was measured using moisture analyser. Tailing sand with allowable moisture content ranging from 3 to 3.5% (bonded with 3.8%wt clay) and 5.5 to 6% (bonded with 7.4%wt clay) were found to have optimum working range with effective green compression strength and permeability.

Abstract: During the round gravel layer for water stop curtain construction,the failure of water curtain frequently occur.In this paper it points at the actual situation about the round gravel layer,based on the round gravel soil and similar river sand screening experiment,then according to the grading of soil conditions and other related data of the experimental results,it analyses the influence of round gravel soil distribution situation on underground engineering pile.

Abstract: The present paper studies grain growth in the presence of inert particles by performing large-scale simulations using a parallel Monte Carlo Potts model. The effect of the second phase particles on the grain size distribution (GSD) is analyzed. The GSDs diverge markedly from log-normal distribution for normal grain growth case. For the cases with low volume fraction of particles, we find that the grain size distributions approach log-normal as stagnation takes hold. For the cases with a high volume fraction of particles, however, medium-size grains reach the log-normal distribution but both lower and upper tails diverge noticeably from the log-normal distribution over time.

Abstract: Multi-fractal theory is used to detect fractal behaviors embedded in grain size distribution ofsinter with low SiO2. Impacts of SiO2, basicity, and MgO on structures of sinter ore are measured quantitatively by means of fractal dimension dm, d(1) and multi-fractal strength Δd. Increase of SiO2 induces decrease of fractal dimension and multi-fractal strength. While proper levels of carbon, basicity, and MgO lead to minimum values of fractal dimension and multi-fractal strength. This kind of quantitative measurement of structures in sinter ore can help us to investigate the relation of mechanical properties and structures in a quantitative way.

Abstract: The aim of the present research work is to examine the influence of mineral composition and grain size distribution on the properties of limestone and dolomite mineral fillers used in Hungarian road construction. Since these properties fundamentally define the features of asphalt pavements, our research goals were assigned accordingly. Different fractions of two mineral fillers (limestone from Alsózsolca and dolomite from Pilisvörösvár) were compared. We have observed deviations in the grain size distribution of some fractions of fillers that were free of contaminations. While limestone consists of a great amount of fines and a relatively small amount of coarse grains, in case of dolomite it is the opposite, that is, small amount of fines and greater amount of coarse grains. The decrease of the grain size of fractions resulted in a slight increase of specific surface area of fillers. We have observed that by the decrease of the grain size of fillers, the hydrophilic coefficient has also decreased. The increasing presence of fines however, resulted in the decrease of the hydrophilic coefficient.

Abstract: 2D Potts model Monte Carlo simulation was carried out on a square lattice to investigate the effects of varying the size of second phase particles on the Zener limit of grain growth, in two-phase polycrystals. Simulations were carried out on a 1000^2 size matrix with Q-state of 64, dispersed with second phase particles of various sizes and surface fractions, and run to stagnation. Different grain growth parameters such as mean grain size, largest grain size, fraction of second phase particles lying on grain boundaries, etc., were computed for the pinned microstructures. The pinned average grain size or the Zener limit increased with increase in particle size, as per the classic Smith-Zener equation. The Zener limit scaled inversely with the square root of the particle fraction for all particle sizes, while it scaled exponentially with the fraction of second phase particles lying on the grain boundaries (ϕ), for all particle sizes tested.

Abstract: Size effects observed in nanocrystalline grain growth are modeled by attributing each type of grain boundary junction an own specific energy and finite mobility. By considering grain growth as a dissipative process that is driven by the reduction of the Gibbs free interface and junction energy a general grain evolution equation is derived that separates into nine types of possible growth kinetics. The corresponding self-similar grain size distributions are derived and compared with results from modified Monte Carlo Potts model simulations taking into account size effects in triple and quadruple junction limited grain growth.

Abstract: Normal and abnormal grain coarsening, NGC and AGC, are briefly reviewed and discussed in the light of grain curvature and kinetic models - notably those of Mullins. The critical importance of the log-normal grain size distribution determined by Hull and the grain shapes measured by Rhines and Craig are reviewed. It is shown that in NGC, as in particle coarsening, the largest grains or particles in their respective distributions grow at the rates, larger by a factor of the ratio of the largest to average size, required to maintain the size distributions during coarsening. The particle curvature removal model for NGC anchorage, giving = 0.2 r/f, developed here, matches surprisingly well the data reviewed by Manohar et al. Finally the need is indicated for further experimental and modeling studies to test the current ideas and to answer the many remaining questions.

Abstract: The sliding frictional contact problem for a laterally graded half-plane has been considered. Two finite element (FE) models, in macro and micro scales have been developed to investigate the effective parameters in contact mechanics of laterally graded materials loaded by flat and triangular rigid stamps. In macro scale model, the laterally graded half-plane is discretized by piecewise homogeneous layers for which the material properties are specified at the centroids by Mori-Tanaka method. In micro scale model, functionally graded material (FGM) structure has been modeled as ideal solid quadrant particles which are spatially distributed in a homogeneous matrix. Boundary conditions and loading is the same in both models. The microstructure has modeled as rearrangement and sizes changing of particles are possible to provide the possibility of crack nucleation investigation in non-singular regions. Analyses and comparison of the results showed that micro and macro scale results are in very good agreement. Also, increasing the grains aspect ratio and using optimum distribution of grains decrease stress distribution roughness on the surface. Therefore, the possibility of surface cracking far from stamp’s edges decreased.