30 research outputs found
Numerical Investigation of Coefficient of Friction in Copper Powder Compaction Process at Micro Scale
No full text7th International Conference on Mechanical and Aerospace Engineering (ICMAE) -- JUL 18-20, 2016 -- London, ENGLANDguner, faruk/0000-0002-3438-0553; SOFUOGLU, HASAN/0000-0002-8433-4045WOS: 000390417000023Multi Particle Finite Element Method (MPFEM) which is a power full approach for particle systems analyzes particle interactions via different friction models. In this study, Amontons-Coulomb constant friction (ACM), Wanheim/Bay generalized friction (WBM) and Levanov's friction models (LFM) are utilized in MPFEM in order to obtain coefficient of friction at particle-particle and particle- die wall interactions in spherical copper powder compaction. Friction models are introduced into the analysis by user subroutines. Compaction processes at room temperature and at 270 degrees C were investigated by terms of coefficient of friction, shear stress and equivalent strain. Although equivalent strain curve of WBM and LFM are in good agreement, ACM resulted in higher equivalent strain and shear stress values. Coefficient of friction those were obtained with WBM and LFM varies in a reasonable range.IEE
An investigation of contact interactions in powder compaction process through variable friction models
No full textguner, faruk/0000-0002-3438-0553; SOFUOGLU, HASAN/0000-0002-8433-4045WOS: 000371100800001In this study, multiparticle finite element (MPFE) approach was used to analyze contact interactions of spherical copper particles in powder compaction process. To this goal, 74 spherical copper particles of 200 in diameter were modeled as individual elastic-plastic bodies, and randomly filled into a die cavity. Interparticle and die-wall-particle contact interactions were investigated, and coefficients of friction were obtained using variable friction models; Wanheim-Bay's general friction model and Levanov's friction model. Variable friction models were incorporated into FE analyses through user subroutines. It was found that the variation of contact stresses inside the die leads to different contact conditions at different zones. The range of coefficient of friction encountered in the analysis was found to be slightly higher in Levanov's friction model than that for Wanheim-Bay's general friction model. On the other hand, Levanov's model was found to be more appropriate for elevated temperature analyses. (C) 2015 Elsevier Ltd. All rights reserved
Effects of friction models on the compaction behavior of copper powder
No full textguner, faruk/0000-0002-3438-0553; SOFUOGLU, HASAN/0000-0002-8433-4045WOS: 000430522500015A comparative numerical and experimental analysis of metal powder compaction processes was presented. Closed-die compaction of spherical copper particles with a nominal diameter of 200 pm was analyzed using Multi Particle Finite Element Method (MPFEM). The von Mises material model associated with contact sensing algorithms was employed to investigate variation of coefficient of friction, and contact interactions between powder particles as well as particles with the die walls. Three different friction models (Amonton-Coulomb, Wertheim Bay, and Levanov) were used to provide a better insight and the latter two were integrated into the commercial finite element package via user-subroutines. To verify the established model, some compaction experiments were carried out. Optical, and scanning electron microscopy analyses were performed, and images obtained were compared with the numerical results. The values of the coefficient of friction obtained using Wanheim-Bay and Levanov friction models fall into the range of 0.04-0.07. From the stress distribution perspective, it was observed that the results obtained with Wanheim-Bay friction model were more conforming to experimental cases where high relative density compaction takes place while Levanov friction model was found to be preferable at low relative density compaction process
Effects of Process Parameters on Copper Powder Compaction Process Using Multi-Particle Finite Element Method
No full text9th International Conference on Tribology (Balkantrib) -- SEP 13-15, 2017 -- TURKEYguner, faruk/0000-0002-3438-0553; SOFUOGLU, HASAN/0000-0002-8433-4045WOS: 000448617300027Powder metallurgy (PM) has been widely used in several industries; especially automotive and aerospace industries and powder metallurgy products grow up every year. The mechanical properties of the final product that is obtained by cold compaction and sintering in powder metallurgy are closely related to the final relative density of the process. The distribution of the relative density in the die is affected by parameters such as compaction velocity, friction coefficient and temperature. Moreover, most of the numerical studies utilizing finite element approaches treat the examined environment as a continuous media with uniformly homogeneous porosity whereas Multi-Particle Finite Element Method (MPFEM) treats every particles as an individual body. In MPFEM, each of the particles can be defined as an elastic-plastic deformable body, so the interactions of the particles with each other and the die wall can be investigated. In this study, each particle was modelled and analyzed as individual deformable body with 3D tetrahedral elements by using MPFEM approach. This study, therefore, was performed to investigate the effects of different temperatures and compaction velocities on stress distribution and deformations of copper powders of 200 mu m-diameter in compaction process. Furthermore, 3-D MPFEM model utilized von Mises material model and constant coefficient of friction of mu=0.05. In addition to MPFEM approach, continuum modelling approach was also performed for comparison purposes.Petroyag Lubricants, UCTEA, TMMO
Physical modeling of extrusion process
No full textMany metal forming processes can be simulated by using the Physical Modeling Technique which requires an inexpensive and small amount of apparatus. The underlying principle behind the Physical Modeling Technique is to simulate the actual metal forming process by selecting a model material and die geometry that closely resemble the actual metal forming process. Typical modeling materials are PLASTICINE, wax and lead while the typical die models are usually made of aluminum, wood or plexiglass.
In two-dimensional analyses, a square or circular grid pattern is printed on the surface of the specimen using ink and a grid stencil. The common method of generating the grid pattern is to use different types of PLASTICINE instead of using ink. Therefore, alternating slabs of PLASTICINE of different colors automatically form the grid patterns.
In the first phase of this study, 16 types of PLASTICINE were tested, via standard compression tests, in order to determine their flow behavior and to identify a pair with similar behavior.
In the second phase of this study, three-dimensional extrusion process was studied by using two types of PLASTICINE as a modeling material while using plexiglass as chamber and die material. The friction coefficient of PLASTICINE was obtained by utilizing the ring compression test. Analysis of deformation patterns, using the well established Physical Modeling Technique, is normally carried out by prescribing a grid pattern on the surface of modeling material.
The extrusion experiments were conducted at the three different area reductions for three different semi-cone die angles. In each case, the plastic strain distributions were determined analyzing the deformed and undeformed grids.
The main objective of this study was to simulate the three-dimensional extrusion process by using PLASTICINE as a modeling medium. Since PLASTICINE is available in 16 different colors, it became necessary to characterize the mechanical behavior of 16 different types of PLASTICINE. The objective was also to identify color pairs of PLASTICINE with similar mechanical behavior and to use these color pairs for the three-dimensional extrusion process. Furthermore, the objectives were to determine the strain distributions of plastic strain components along the diameter of an extruded product and to determine the effects of the process variables, such as area reduction and semi-cone die angle, on the required forming load
Physical modeling and finite element analysis of friction encountered in large deformation processes
No full textThe main objective of this research was to investigate the role of frictional forces in large deformation metal forming processes, such as forging and extrusion. The research included analysis of deformation in the above processes using both the Physical Modeling Technique (PMT) and the Finite Element Method (FEM) with the goal of identifying friction effects.
In this research, all experiments were conducted by utilizing PMT to simulate actual metal forming processes by selecting a model material and die geometry that resemble the conditions of an actual metal forming process. All physical modeling experiments were conducted using plasticine, as model material, and plexiglass as the die material.
A new method was developed to obtain constant strain-rate {a — e) curves utilizing the data obtained from a testing machine in which the croshead moves with a constant speed. The flow characteristics and the strain-rate sensitivities of two types of plasticine were determined from several compression tests. Compression test data were analyzed by using a statistical method, 2 factorial design, in order to identify the effects of deformation speed, lubrication and material type on friction and the mechanical behaviors of the materials. A series of ring compression tests were conducted to determine the coefficient of friction, p, and the corresponding calibration curve for different types of lubricants. A new technique, utilizing open-die backward extrusion test, was developed as an alternative method for evaluating the coefficient of friction by relating the percentage of deformation to the extruded height.
The experimental results showed that two types of plasticine have different material properties while being strain-rate dependent at room temperature. It was also shown that the extruded height changes according to the friction conditions at the interface.
In the second phase of this study, ABAQUS, a general purpose finite element code, was employed for the FE analysis of forming processes. Ring compression tests were simulated in order to investigate the effects of material type, deformation speed, barreling, and strain-rate sensitivity on the calibration curves. Compression tests were modeled for different aspect ratios. The effect of aspect ratios on the normal pressure and friction stress was determined. Open-die backward extrusion for different die sizes were also modeled to obtain the normal pressures, frictional stresses, and the calibration curves. Contrary to the results available in the literature, the finite element analysis results showed that every material possesses a distinctive calibration curve which is different than that of a different material.
The experimental and numerical results indicate that material properties play an important role in the behavior of calibration curves obtained from the ring compression test. The numerical results also show that open-die backward extrusion can be used to generate calibration curves for evaluating ì
Sustainable bio-nano composite coatings for the protection of marble surfaces
No full textWater repellency on natural stone surfaces is the most important issue in the protection of stone monuments from effects of atmospheric pollutants. In this study, effectiveness of a bio-nano composite coating, composed of a biodegradable polymer (poly-L-lactide [PLA]) and montmorillonite clay (MMT) was investigated for the protection of marble surfaces from pollution. The clay dispersion in polymer matrices was analyzed by using Scanning Tunnel Electron Microscopy (STEM) and X-Ray Diffraction (XRD), while protection performance was investigated by the measurement of surface roughness, wettability, water vapor permeability, capillary water absorption, and color changes on the marble surfaces. As a result, no alteration on the color of coated marbles was observed, significant improvement was obtained for hydrophobicity of the surface and inhibition of sulfation reaction on the exposed marble surfaces under acidic atmosphere. It could be said that PLA based nanocomposites seem to be promising materials as protective coating agents in reducing the effects of water and atmospheric pollutants on marble surfaces.Scientific and Technical Research Council of Turkey (108M335
A statistical approach to explore cemented total hip reconstruction performance
No full textThis study was carried out to determine mechanical behavior and bone adaptation of total hip arthroplasty (THA) subject to concentrated and distributed muscle loads and hip contact forces during activities of walking and stair climbing. Finite element modeling of THA with different prostheses, activity and loading types was developed by adopting a statistical method. Two levels of prostheses, activity, and loading types were selected for the study. 2(3) factorial method was then pursued to design input and output data of finite element analysis. Maximum von Mises stresses were chosen to be output data on which statistical investigation was performed to investigate contribution and interaction of main factors on mechanical failure of cemented THA reconstructions by utilizing analysis of variance method (ANOVA). This study illustrated that the maximum von Mises stresses of THA showed considerable variation for main factors and their two-factor interactions
