Browsing by Subject "Strength of materials"
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Item Mechanical properties and wear strengths in aluminiumalumina composites(RILEM Publications, 1998) Atïk E.In this study, after producing metal matrix composite materials reinforced with ceramic particles by adding hard Al2O3 particles into a selected ageable aluminum alloy, the wear strengths were investigated. Composites of aluminum alloys containing 2 to 10 wt of Al2O3 particles in the size range of 23.4 to 108 μm were prepared by adding alumina particles to a partially-solid vigorouslyagitated matrix alloy. For a given tribologic system, the sizes and ratios of optimum particles were determined from the point of the wear strengths of these materials, of which the wear strengths greatly increased according to the matrix materials. Alumina particles were subjected to preheating at 500°C for 8 hours. Particles were added into the alumina alloy heated up to semi-solid/ semi-liquid phase interval in an argon medium by using a mixer. Then furnace temperature was raised up to 800°C step by step. Later the composite materials were die cast and solidified and aged. The behavior of the composites was studied by using a pin-on-disk type machine. The largest wear strengths were obtained at an average particle size of 76.5 μm and percentage of 4% wt Al2O3. Increase in the wear strength of the composites was obtained as 3.85 times the wear strength of the matrix material.Item Investigation on the elastic modulus and density of vacuum casted aluminum alloy 2024 containing lithium additions(ASM International, 2000) Meric C.The elastic modulus and density of (2024+LiX) alloys are investigated. To the alloy of 2024, the weight percentages of lithium added are 2, 3, and 4. Melting is carried out in an induction furnace under argon gas protection; casting is done under vacuum. To obtain the maximum strength and hardness, the specimens are solution heat treated under 495 °C and quenched in water at room temperature. Then, they are aged naturally and artificially. For the purposes of comparing, some of the specimens are melted under argon gas, but casting is done without vacuum. All the specimens are subjected to tension tests. As a result of this work, the alloys of aluminum that are difficult to manufacture by the known methods are manufactured safely by the vacuum casting method. For 1% of lithium added to the alloy, an increase of 6% in the elastic modulus and 3% decrease in the density are obtained. The specific elastic modulus, E/ρ, ratio increases by about 10% for each 1% addition of lithium.Item Interactions between components in coking of coal blends; [KömüR Karişimlarinin Koklaştirilmasinda Bi̇leşenler Arasi Eti̇ki̇leşi̇mler](2004) Kemal M.; Arslan V.; Cengizler H.This study has been carried out for the purpose of determination of interactions among the components in coal blends during the coking process. For this purpose, the blends of cokable Zonguldak coal (ZK) with air-dried (TK), semicoked both at 550°C (TK550) and 900°C (TK900) Tunçbilek lignite were prepared. The plasticity, dilatation, contraction of these blends and the strength of the cokes produced from these blends were determined. The experimental data obtained were evaluated and it was determined that the lignite, when carbonised at about 500°C, completes its chemical breakdown, terminates the evolution of its volatile matter and contraction process, improves its surface wetting behavior and thus exhibits the most favorable properties as far as the cokability of coal blend is concerned.Item Determination of hardness of AA 2004 aluminium alloy under ageing conditions by means of artificial neural networks method(2004) Atik E.; Meric C.; Karlik B.As known, 2XXX and 7XXX Aluminium wrought alloys can have high strength values by means of precipitation hardening heat treatment. Determination of the precipitation hardening conditions, which can give the most suitable strength values of an alloy, requires numerous tests. But the results of this process which require long time and high cost can be obtained in a shorter time and at a lower cost with less data by means of Artificial Neural Networks method. Since this method is used, less number of experiments and therefore less data are needed. Then other values are found by means of Artificial Neural Networks (ANN) method. This paper, presents the feed forward ANN to determine hardness of alloy for different temperatures. For this purpose, a classic Back-Propagation Algorithm was used that is structure as 1:2:4.Item Prediction of effects of microstructural phases using generalized regression neural network(2012) Ozturk A.U.; Turan M.E.In the scope of this study, microstructure-macroproperty relationship of cement mortars has been established in order to define the effects of microstructural phases on strength. Microstructural studies have been become great issue in materials engineering. Nowadays, to characterize the microstructural phase properties and to improve and modify them are performed by scientist to forecasting and enhancing. According to this objective, cement mortars incorporating with chemical admixtures were prepared to constitute different microstructural graphs. These micrographs were analyzed to determine the amounts of unhydrated cement part, undifferentiated hydrated part and capillary pore phases in the cement mortar sections. Afterwards, the amounts of these microstructural phases were related to strength values of each cement mortar specimen. The relationship was established by using generalized regression neural network analysis. © 2011 Elsevier Ltd. All rights reserved.Item Specific surface area effect on compressibility behaviour of clayey soils(2013) Yukselen-Aksoy Y.; Kaya A.In this study, the effect of specific surface area on compressibility and permeability characteristics of remoulded and intact clayey soils was investigated. Fifteen remoulded and 15 intact soils with a wide range of physicochemical properties were tested. The results indicate that specific surface area has a significant effect on compressibility and permeability behaviour of clayey soils. In addition to other soil index properties, specific surface area can be used for estimating these engineering properties. Significantly high correlation coefficient (r = 0.97) between compression index (Cc) and the specific surface area is observed for remoulded clayey soils with only methylene blue-spot specific surface area. There is no significant correlation between the BET-N2 specific surface area and Cc: The effect of the remoulded water content on proposed specific surface area and Cc relationship is also investigated. The results show that as specific surface area of soils increases, cv decreases, indicating the importance of the diffuse double layer on the consolidation process. The results also reveal that permeability is controlled by the specific surface area of soils. In addition, the data obtained in this study indicate that there is a linear correlation between Cc/n0 and Cc, which indicates the significance of initial void ratio on the compressibility characteristics of soils.Item Strengthening of brick masonry with PVA fiber reinforced cement stucco(Elsevier Ltd, 2015) Arisoy B.; Ercan E.; Demir A.This paper presents the behavior of masonry walls externally strengthened by poly vinyl alcohol (PVA) fiber reinforced cement plaster. Tensile weakness of masonry wall is improved by simply applying fiber reinforced cement (FRC) plaster on masonry surface. Strengthening by ductile materials, in order to maintain ductile behavior of masonry to resist shear forces would provide reduction in the crack development and crack width providing delay in failure. FRC was applied to surfaces of the masonry wall as stucco to prevent crack growth under shear effect. An experimental program was performed to study the response of unreinforced and retrofitted masonry walls with externally applied fiber reinforced cement mixture, under shear and compressive loading. The experimental results indicate that retrofitting masonry walls with PVA fiber reinforced cement stucco increases the shear strength of the wall approximately half times in solid and high strength brick walls, 2.5 times in regular brick walls. © 2015 Elsevier Ltd. All rights reserved.Item Investigations into factors influencing the CBR values of some Aegean sands(Sharif University of Technology, 2016) Erzin Y.; Türköz D.; Tuskan Y.; Yilmaz I.The California Bearing Ratio (CBR) value of the soils is very important for geotechnical engineering and earth structures. A CBR value is affected by the soil type and different soil properties. With this in view, in this paper, an attempt has been made for investigating the factors that affect the CBR values of some Aegean sands collected from nine different locations in Manisa (Turkey). The sand samples were tested for mineralogy, particle shape and size, and specific gravity. The CBR tests were then performed on these samples at different dry densities to examine the influence of dry density, relative density, water content, and particle shape and size on the CBR value. Multiple Regression Analysis (MRA) was performed to predict the CBR value of the sands by using the experimental results. Moreover, several performance indices, such as coefficient of correlation and variance account for mean absolute error and root mean square error, were calculated to check the prediction capacity of the proposed MR equation. The obtained indices make it clear that the equation derived from the samples used in this study applies well, with an acceptable accuracy, to the CBR estimation at the preliminary stage of site investigations. © 2016 Sharif University of Technology. All rights reserved.Item Use of neural networks for the prediction of the CBR value of some Aegean sands(Springer-Verlag London Ltd, 2016) Erzin Y.; Turkoz D.This study deals with the development of an artificial neural network (ANN) and a multiple regression (MR) model that can be employed for estimating the California bearing ratio (CBR) value of some Aegean sands. To achieve this, the results of CBR tests performed on the compacted specimens of nine different Aegean sands with varying soil properties were used in the development of the ANN and MR models. The results of the ANN and MR models were compared with those obtained from the experiments. It is found that the CBR values predicted from the ANN model matched the experimental values much better than the MR model. Moreover, several performance indices, such as coefficient of determination, root-mean-square error, mean absolute error, and variance, were used to evaluate the prediction performance of the ANN and MR models. The ANN model has shown higher prediction performance than the MR model based on the performance indices, which demonstrates the usefulness and efficiency of the ANN model. Thus, the ANN model can be used to predict CBR value of the Aegean sands included in this study as an inexpensive substitute for the laboratory testing, quite easily and efficiently. © 2015, The Natural Computing Applications Forum.Item Investigation of in-plane and out-of-plane wall behavior related to lateral loading depending on wall profiles and opening arrangements in Hellenistic Towers; [Helenistik kulelerde yanal yüke ilişkin düzlem içi ve düzlem dışı duvar davranışının duvar profilleri ve açıklık düzenlerine bağlı olarak incelenmesi](Gazi Universitesi Muhendislik-Mimarlik, 2020) Gençer F.; Hamamcıoğlu-Turan M.; Aktaş E.Dry masonry wall profiles constructed without using bonding material between blocks are encountered in different building types dated to Greek, Hellenistic and Roman periods. Depending on development of earthquake experiences, dry masonry wall profiles vary in terms of wall thickness, number of layers, relationship of layers and size, form, organization and relationship of blocks. In this study, the construction details increasing the structural strength in watch towers constructed in Hellenistic Period are aimed to be determined. This study is limited with investigation of effect of wall profiles and opening organizations on in-plane and out-of-plane wall behaviors under lateral loading. Primarily, wall profiles and opening types of dry masonry towers in ancient Caria, Pamphylia and Cilicia regions, that have not lost authenticity and integrity or had information about their authentic form, were documented. By using gathered data, hypothetic towers with different wall profiles and opening types are designed. To determine in-plane and out-of-plane wall behavior of hypothetic towers, simulation of quasi-static tilt analysis based on equilibrium were carried out, and form changes at walls and collapse angles of towers were identified. Wall profile and opening properties effecting on structural strength under lateral loading were determinedd. © 2020 Gazi Universitesi Muhendislik-Mimarlik. All rights reserved.