Papers by Keyword: Shape Factor

Abstract: The article discusses the application of the discrete element method (DEM) for modeling the behavior of spherical particles in granular media. Key aspects of particle contact interactions, including frictional forces, elasticity, coordination number, and the shape factor of spherical particles, are analyzed and investigated. It is worth noting that the proposed methodology enables the study of the mechanical properties of systems with particles of various sizes and compositions, as well as the modeling of their behavior in confined spaces and under dynamic influences. The modeling results demonstrate the high accuracy and versatility of the DEM for analyzing processes in bulk materials, particularly transportation, mixing, and granulation. The findings underscore the effectiveness of using DEM to solve complex problems and highlight prospects for its further improvement.

Abstract: Metal direct writing in semi-solid slurry is an innovative technology to realize low-cost printing of load-bearing parts in contrast to laser-based additive manufacturing. However, it is challenging to achieve near net-forming of 3D parts in the current stage because of the out of controlled microstructure and hence the unstable macro extrusion of the used semi-solid slurry. Here, mixed powder remelting (MPR) is introduced to actively design the characteristics of solid phases, i.e., solid fraction, shape factor, and size distribution. Specifically, high-melting-point pure Al powder served as the dispersed solid phases in the liquid phase that transformed from Al-Si alloy powder after remelting, leading to hypoeutectic Al-Si semi-solid slurry. The effectiveness of this approach was experimentally examined and kinetically modelled, to prepare semi-solid slurry with pre-set microstructure. The improved extrusion stability of semi-solid slurry can be anticipated, and it is universal for manufacturing of metal matrix composites slurry.

Abstract: The wheelchair has become today indispensable for people experiencing various locomotor disabilities. By investigating the current concepts of solutions to improve the ability to move physically, it was attempted to propose a typology to address the mobility problem. On a basic manual wheelchair, a system will be attached to ensure overcoming the obstacles and to guarantee maintaining the stability of the entire wheelchair. This adjustment will improve the user independence and offer the option of attaching a group of wheels to facilitate smooth movement. By using the Ashby’s graphs that compare the ratio between different properties and by calculating the material index, the optimum material will be determine for the developed system. Ansys software was used to study the structural behaviour under the given boundary conditions by determining the total deformation and equivalent Von Misses stress and then comparisons were made between the obtained results. Also, through topology optimization the most strained areas were discovered and measures were proposed to remedy them.

Abstract: This work presents the results of investigations of the topological characteristics of quartz raw materials of various mineral compositions crushed to the critical state of the dispersed layer under which the shape of the particles and the action of the electrostatic repulsion forces change.

Abstract: The article is devoted to the problems of fractioning the general abrasive mass into the fractions of certain shape grains. The methods of separation of bulk materials have been analyzed. The designs are considered and the operating principle of the original units for abrasive separation is described. The revealed regularities at the separation of abrasive masses of various granularities are presented.

Abstract: Measurements of basic materials properties of building materials with pozzolanic waste admixture originated from grinding of thermally insulating bricks were performed by means of pycnometry method. Besides, the thermal conductivity dependence on the moisture content measurements were carried out by using a non-stationary pulse method. Obtained data were subsequently analyzed by simple Wiener’s bounds and sophisticated homogenization formula taking into account the shape of ellipsoidal pore inclusions. Validity of applied homogenization models were assessed by comparison of the measured and the calculated data. On the basis of experimental data and homogenization analysis, the shape effect on the thermal conductivity is discussed.

Abstract: The unique properties of rare earth elements (REE) have resulted in their being crucial to a growing number of emerging technologies. As the demand for REE currently exceeds annual production, the present worldwide crisis for REE will probably continue for the foreseeable future. Hence, it is highly likely that the availability of REE used in the metallurgy of cast iron will be significantly reduced and alternatives to REE usage may have to be developed. Graphite nodules nucleate heterogeneously on particles formed in the melt, having a duplex structure (sulphide as a core and oxide/silicate as a shell). Mg, Ca and REE appear to act in the nucleation first stage, while Si, Al, Mg, REE, Ca, Sr and Ba act predominately in the second stage. Generally, REE are employed in ductile irons to accomplish the following tasks: (a) neutralize tramp elements such as Ti, Pb, Bi, As etc; (b) assist in nodulizing or provide a supplementary effect to Mg to promote spheroidal graphite shapes; (c) assist in nucleating graphite. When anti-nodularising Thielman control factors (K) are less than 0.8, REE are usually not required since there are no trace elements to neutralize. REE are useful for K factors between 0.80 to 1.20 and are mandatory for K factors greater than 1.20. Theilman factors greater than 2.0 will always require REE. When Theilman factors are less than 0.80, REE _res levels of 0.01% are usually more than sufficient for ductile iron production. Three ductile iron inoculation alloys were selected for this research: (a) a conventional Ca bearing 75% FeSi inoculant (Ca-FeSi), used at a high consumption level; (b) an improved conventional Ca-FeSi alloy that incorporated active inoculating elements, such as Ba or REE, used at a medium consumption level, and (c) a combination of a commercial inoculant, such as Ca-FeSi alloy, used with a separate oxy-sulphide inoculant enhancer alloy addition. The last inoculation variant provided the best structural parameters and the lowest consumption level.

Abstract: The authors have investigated, in other paper, the problem related to the definition of a “set of shape factors” in order to declare the feasibility of a product through sheet hydroforming. In particular the defined shape factors are three different a-dimensional coefficients by which it is possible to declare the feasibility of a product through the calculation, in different sections, of the three previous shape factors. The robustness of this methodology is related to the correct calculation of the “limit value” of each shape factor. In fact the feasibility is reached if, in any section, the calculated shape factors are higher than their respective limit values. In this paper the authors have performed an extensive numerical and experimental campaign, taking into account a different geometry respect to that of the first paper, in order to: re-calculate the limit value for each shape factor and, then, verify the correctness of the limit values exposed in the previous first paper. The numerical campaign has been used, after the evaluation of the accuracy of the numerical model, in order to study the feasibility of the product without engaging the hydroforming machine. Finite Element Analysis (FEA) has been extensively used in order to investigate and define each shape factor with a proper comparison to the macro feasibility of the chosen component geometry. The limit values that have been calculated by the authors in this paper are slightly different from those calculated in the first paper. From this point of view it is possible that, although the shape factors are a-dimensional coefficients, they are affected by different choices of the users as, for example, the dimensions of the initial blank. Anyway, the small differences in the shape factors limit values do not adversely affect the use of the shape factors in order to predict the feasibility of the product.

Abstract: Thixoforming technology has made considerable advances since its initial discovery in 1973. Although, after almost 40 years, few raw materials are still used as thixoforming materials. The Al-Si-Mg alloys often used for semi-solid state processing are notably casting alloys like A356 and A357. The development of new alloys specially tailored for thixoforming is a new challenge in this area of research. This paper will present some results related to the study of Al-2wt%Si-05wt%Mg and Al-4wt%Si-05wt%Mg alloy obtained via conventional foundry followed by ultra-refining. The results are compared with a commercial Al-7wt%Si-05wt%Mg alloy. Also presents its morphological evolution in the re-heating of the material to obtain the solid fraction of 45% and 60% in four different holding times 0, 30, 90 e 210 seconds. After re-heating, with the determination of grain size and globules, held the study Rheocast Quality Index (RQI) and Shape Factor (SF), parameter that helps to quantify the efficiency of the treatment globularization to obtain semi-solid structure with globular structure. The morphological evolution showed that the increase of holding time resulted in a minor increase in the globule size of the structure. The RQI values show that there is little morphological evolution in the treatment of globularization for alloys with percentage of Si, indicating alloys with percentage below of 4wt% Si is the most appropriate for thixoforming.

Abstract: Boundary layers are affected by a number of different factors. Transition of the boundary layer is very sensitive to changes in geometry, velocity and turbulence levels. An understanding of the flow characteristics over a flat plate subjected to changes in geometry, velocity and turbulence is essential to try and understand boundary layer transition. Experiments were conducted in Low Turbulence wind tunnel (LTWT) at Northwestern Polytechnical University (NWPU), China to understand the effects due to changes in geometric profiles on boundary layer transition. The leading edge of the flat plate was changed and several different configurations ranging from Aspect Ratio (AR) 1 to 12 were used. Turbulence level was kept constant at 0.02% and the velocity was kept at default value of 30 m/s. The results indicated that as the AR increases, boundary layer thickness reduces at the same location along the plate. The displacement thickness shows that the fluctuations increase with an increase with AR which denotes the effect of leading edge on turbulence spot’s production. For AR≥4, an increase in AR led to an elongation of the transition zone and a delay in transition onset. Nomenclature