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- MakaleAçık Erişim2026Scopus SJRQ2Relationship Between Aluminum Liquid Metal Quality and Defects
Kutsal, Umit; Colak, Murat; Ertugrul, Onur
Aluminum alloys are commonly used in various industries today. In order to produce defect-free high-quality alloys with sustainable processes, defects must be reduced, and liquid metal quality must be improved. There are various methods that can be used for the measurement of liquid metal quality. Some of which are density index, bifilm index, K-Mold index, PoDFA, Prefil, fluidity test, and thermal analysis. The relationship and validation between these methods are still not clear. In this study, the relationship between aluminum liquid metal quality and defects is analyzed. Three different conditions were utilized. These conditions are (1) before a controlled degassing, (2) after the controlled degassing and (3) after the liquid metal is transferred to the holding furnace. According to the results, it was observed that the reduction of bifilms index did not reduce other inclusions and did not always favorably affect other measurement methods. It was also observed that the reduction of bifilm index did not improve the porosity level. Moreover, it was found that elongation values are related to the largest defect diameters. Bifilm index are not the only factor affecting the elongation and the density index directly affects the defect distribution. K-Mold index has an impact as it shows macro-inclusions. However, bifilm index, density index, fluidity index and K-Mold index are not as sufficient as numerical calculation of defect size by computed tomography (CT). The main factor directly affecting the elongation and tensile strength was found to be the inclusion size and diameter in the CT result. Examination of the fracture surfaces revealed that oxide contents are present, and the oxygen orientations and aluminum orientations are compatible. This harmony is thought to be related to the orientation of the bifilms in the structure.
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İncele - MakaleAçık Erişim2024Scopus SJRQ2Mixed series solution for vibration and stability of porous bi-directional functionally graded beams
Turan, Muhittin
A new analytical solution based on the Ritz method is presented in this paper for analyzing the free vibration and buckling behavior of porous bi-directional functionally graded (2D-FG) beams under various boundary conditions. The solution is based on first-order shear deformation theory (FSDT). The selection of solution functions used in Ritz methods distinguishes the methods from each other and determines the accuracy of the analytical solution. To accurately capture the system's behavior and achieve the desired results, these functions have been carefully selected as a combination of polynomial and trigonometric expressions tailored as mixed series functions for each boundary condition. The study considers three types of porosity, namely PFG-1, PFG-2, and PFG-3. The equations of motion are derived using Lagrange's principle, taking into account the power-law variation of the beam material components throughout the volume. The non-dimensional fundamental frequencies and critical buckling loads are calculated for different boundary conditions, gradation exponents in the x and z directions (px, pz), slenderness (L/h), porosity coefficient (e), and porosity types. Initially, the accuracy of the mixed series functions is investigated for non-porous bi-directional functionally graded beams, and the numerical results are compared with existing literature to validate the proposed solution. Subsequently, the paper focuses on analyzing the influence of porosity on the free vibration and buckling behavior of bi-directional functionally graded beams using the developed solution method.
AtıfScopus21WoS22OpenAlex18İncele - MakaleAçık Erişim2023Scopus SJRQ1A new approach for high-quality production of UHMWPE by applying powder vibration densification before sintering
Yilmaz, Galip; Uslu, Emin
Due to its extreme viscosity, UHMWPE powder requires elevated pressure and temperature settings to ensure a fully solid structure. But a gentle process is vital for reliability in certain applications, such as prosthetic liners. A unique type of large gap, not mentioned in the literature, has been observed to resist closing more than regular gaps due to the number of particles forming a shield against pressure. As a solution, a mechanical vibration treatment of the particles before heating was used to eliminate these particular large gaps. Optimum vibration parameters were found, and the samples' final solid density and mechanical properties increased. The particles' dimensions and coefficient of friction were measured, and their vibration-dependent characteristics were discussed. A custom-made microscope apparatus was used to observe the vibration-induced densification of the particles and the gaps resisting closing.
AtıfScopus14WoS14İncele - MakaleAçık Erişim2021Scopus SJRQ3Role of metal quality and porosity formation in low pressure die casting of A356: Experimental observations
Gursoy, O.; Nordmak, A.; Syvertsen, F.; Colak, M.; Tur, K.; Dispinar, D.
Porosity is one of the major problems in casting operations and there are several discussions in the literature about the porosity formation in aluminum castings. Bifilms are the defects that are introduced into the melt by turbulence. They can be detected with reduced pressure test and presented numerically by measuring bifilm index. The measure of bifilm index is the sum of total oxide length given in millimeters from the cross-section of reduced pressure test sample solidified under 0.01 MPa. In this work, low pressure die casting (LPDC) unit was built in an attempt to enhance the producibility rate. The unit consists of a pump housing that was placed inside the melt in the melting furnace where the pressure was applied instead of the whole melt surface. It was observed that the melt quality of A356 alloy was deteriorated over time which had led to higher porosity. This was attributed to the increased oxide thickness of the bifilm by the consumption of air in between the folded oxides. A relationship was found between bifilm index and pore formation.
AtıfScopus7WoS6OpenAlex5İncele - MakaleYalnız künye2018Scopus SJRQ2X-ray CT monitoring of macro void development in mortars exposed to sulfate attack
Tekin, Ilker; Birgul, Recep; Aruntas, Huseyin Y.
This study reports the results of nondestructive monitoring of macro void developments in mortars manufactured with both ordinary Portland cement and sulfate resistant cement. Two types of curing were utilized; tap water curing and another curing environment that contains 5% Na2(SO4) solution. Being the primary objective of this study, macro void developments of the mortar specimens were monitored by X-ray Medical Computerized Tomography. Compressive strength tests and water absorption tests were conducted on specimens that were kept in both curing environments for a duration of 560 days. Data analyses yielded consistent results among the three tests used in this experimental study. Macro void ratios of mortars decreased at the beginning of experiments for a certain period; afterwards, macro void ratios increased. The objective of this study was accomplished as anticipated since X-CT image analysis was able to nondestructively monitor macro void development process in cement mortars.
AtıfScopus6WoS6OpenAlex1İncele - MakaleYayıncıda açık erişim2015Scopus SJRQ1Monitoring macro voids in mortars by computerized tomography method
Tekin, Ilker; Birgul, Recep; Ozgur Yaman, Ismail; Gencel, Osman; Yilmaz Aruntas, Huseyin
This study aims to investigate the use of ground pumice powder (PP) in cement production and to monitor void developments in mortars by X-ray Computerized Tomography (CT) which is a nondestructive test method. PP-blended cements were produced by replacing ordinary Portland cement with PP at 0% (control), 5%, 10% and 15% by weight. Paste and mortar specimens were manufactured by these blended cements. Some of the physical and mechanical tests are carried out on these mortar specimens. Experimental results showed that macro void developments in 100-day period for mortars with different PP replacement ratios exhibited different reduction in void ratios.
AtıfScopus19WoS17OpenAlex19İncele