Papers by Keyword: Particle Shape

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Authors: Roger D. Doherty, Elizabeth Hoffman, Christopher Hovanec, Arnaud Lens
Abstract: The prior literature on abnormal grain coarsening (AGC) at low volume fractions (f) of stable second phase particles in high purity Al alloys is reviewed and reanalyzed in the light of developments in modeling particle inhibition of grain boundary migration. With the usual assumptions (i) of incoherent particles that retain their shape on contact with the grain boundaries and (ii) that all the grain boundaries are equally mobile, it appears impossible to account for process of AGC. Normal grain coarsening (NGC) is shown to be less inhibited by the particles than is AGC. This idea is explored using a new but simple model of particle inhibition by curvature removal. The curvature of the smallest grains is always larger than that of the larger grains. Two possible hypotheses to overcome this difficulty are proposed: First the possible change of shape of particles on slowly moving grain boundaries, of grains with near 14 neighbors should, after a small increment of NGC, promote AGC at low values of the volume fraction f. The second hypothesis involves the observed high density of immobile, low angle grain boundaries (LAGBs) found in recent experiments on high purity Al-Fe-Si alloys cast with very coarse grain sizes. These alloys undergo rapid AGC even at higher values of f (> 0.01). These LAGBs are expected to inhibit the shrinkage of many of the small grains, whose loss is the fundamental mechanism of NGC.
Authors: Fábio de Oliveira Arouca, C.G. Azevedo, M.H.A. Oliveira, João Jorge Ribeiro Damasceno
Abstract: The dynamic analysis of behavior of solid particles in porous media such as settling processes are important for the dimensioning increasingly precise of pieces of equipment that promote the solid-liquid separation. Several factors can influence in dynamics of the fall of solid particles into a fluid medium; among them, the shape, distribution of sizes, and particle density. The main objective of this work is to analyze the behavior of solid-solid system based on the shape, size distribution and density of solid particles. The initial settling velocity in batch settling tests and the accommodation of particles in the sediment formed are evaluated for different materials. The gamma-ray attenuation technique was used in the experimental tests. Comparison of results obtained allowed evaluating in an exploratory research the significance of variables involved.
Authors: Sylwia Szerakowska, Maria Jolanta Sulewska, Jerzy Trzciński, Barbara Woronko
Abstract: Definition and studies on the shape of various bodies are an interdisciplinary issue, raising wide interest among scientists. In geology and geotechnics the studies refer to features related to the shape of soil and rock particles, especially of those used for practical purposes. Due to the complex shape of particles, its three components have been distinguished: sphericity, angularity and surface microtexture. Sphericity usually determines the degree of similarity of a given particle to a sphere, whereas defined as a form refers to the general shape of the particle [3]. Particle shape and parameters that characterise it have not been unequivocally defined and normalised, resulting in a large number of definitions and ways of their determination. An extensive paper presenting the definitions used to describe shape parameters has been presented by Szerakowska [13]. This paper is focused on the comparison of analytical methods and an attempt to select the most optimal method for determining sphericity of particles in construction and road aggregates.
Authors: Sylwia Szerakowska, Maria Jolanta Sulewska, Jerzy Trzciński, Barbara Woronko
Abstract: Particle shape raises more interest among geologists than among engineering geotechnical staff. It is commonly accepted that particle shape is the result of geological processes, such as transportation and sedimentation, and depends on many factors, such as mineral composition or structure and texture of the host rock. The influence of particle shape on the geotechnical properties of soil has been widely discussed in literature from the early 1900-ties, e.g. by Wadell [3], Riley [16], Pentland [6] and other scientists, who proposed their own definitions and methods of determining particle roundness and angularity. Finally, it has been decided that particle shape should be defined by three independent parameters [2]: roundness, reflecting the general shape of the particle in comparison to a sphere; angularity, describing changes in roundness in the corners of the studied particle; and microtexture, reflecting the complexity of the particle surface in micro scale; this parameter is also referred to as micromorphology. These three parameters describe particle shape at various magnifications and allow obtaining all important data on this feature. This report is focused on a review and analysis of the analytical methods determining particle angularity, and is an attempt to establish an optimal definition of determining particle angularity in road aggregates. We present selected definitions used to determine angularity, worked out by different authors over the years as an attempt to find the best analytical method of describing angularity.
Authors: Yang Liu, Xiao Zhu Li, Cheng Lin Wang
Abstract: Numerical simulation was conducted to study the particle breakage of rock in rolling compaction (RC) test based on discrete element method (DEM). Different shapes of particles were formed to represent the real particle shape. A quantitative analysis method of particle breakage was proposed according to the grading curve before and after compaction. The numerical results had a good agrrement with the field test, which indicated that the method adopted in this paper was feasibile and could consider the influence of the particle shape on the particle breakage in RC test.
Authors: Tian Xi Liu, Cheng Wei, Liang Ma, Yang Zhao
Abstract: To find out the influence of particle shape on the force situation and sampling efficiency of the drilling tool, the discrete element method is employed to build the lunar regolith model and simulate the interaction between soil and drilling tool. A three-dimensional contact model is introduced to represent the impact between particles. To make sure the validity of the model, a triaxial-test is conducted to optimize the micro-parameters of the model. Then, the model is employed to the simulation of drilling process. From the computational simulation results, conclusions can be made: the particle shape will change the interlocking between particles, and the strip particles have the largest interlocking which makes the force situation largest and the sampling efficiency smallest.
Authors: Yi Dong Xu, Rui Ping Xu
Abstract: Based on the current production line of artificial aggregate, the waste concrete derived from the same source was crushed by different crushing machine, jaw crusher and impact crusher. This paper focuses on the effect of different crushing machine on gradation and particle shape of recycled aggregate. As is shown by the results, recycled aggregate produced by two crushing methods can satisfy the requirements of specifications. Compared with the recycled aggregate produced by impact crusher, the coarse recycled aggregate produced by jaw crusher have less length/breadth ratio and higher thickness/breadth ratio; particle shape can come closer to round.
Authors: Yiu Pong Chan, Chak Yin Tang, Brian W. Darvell, Chi Pong Tsui
Abstract: The effect of filler shape and volume fraction on the micromechanical damage behavior of particulate-reinforced dental composites was investigated using the finite element method. Threedimensional unit cell models for various filler volumes and shapes, using hydroxyapatite in Bis- GMA as a model system, were used. Young’s modulus and stress concentration factor were calculated. The effects of filler shape on the ease of initiation of strain damage in the matrix and onset of particle-matrix debonding are discussed.
Authors: Lydia Anggraini, Yuta Natsume, Kei Ameyama
Abstract: Silicon nitride with 50 mass zirconia ceramic matrix composites were processed by mechanical milling (MM) followed by spark plasma sintering (SPS). Two different of Si3N4 particle shapes for create harmonic microstructure were investigated. The microstructure of Si3N4-ZrO2 with initial Si3N4 shape is like coin/flakes after MM for 144 ks was failed to create the harmonic microstructure after SPS. With another sphere shape of Si3N4 after MM for 144 ks, the harmonic microstructure could be formed after SPS. Thus, the initial powders shape of Si3N4 have an effect in the formation of harmonic microstructure could be fully achieved. The highest mechanical properties of Si3N4-ZrO2 are on the powders with mechanical milling time for 144 ks. The Si3N4 ceramic with homogeneous fine grains of ZrO2 dispersed on its surface was obtained, and the mechanical properties were improved. The Vickers hardness obtained on 144 ks is 1031 MPa and the bending strength is 262 MPa. The main factors explaining the improvement in the mechanical properties of Si3N4-ZrO2 are considered to be the porosity decrease caused by the particles shape and appropriate condition of powder processing i.e. MM and SPS.
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