Volume 63, Issue 11

This study examined the response of low-alloy white cast iron to austempering heat treatment. In addition, it investigated the microstructure and mechanical properties of austempered low-alloy white cast iron. The low-alloy white cast iron specimens were austenitized at 900 °C, followed by quick quenching into a salt bath at 375 °C, and held there for 15 to 120 minutes for austempering heat treatment. Microstructural features were studied by optical, scanning electron microscopes, and XRD analysis. The mechanical properties were determined by hardness and unnotched Charpy impact toughness tests. As a function of those austempering times, a microstructural map was constructed to show how the transformation products develop, quantitatively. The experimental results showed that the austempering heat treatment produced a microstructure consisting of eutectic carbides + ausferritic structure in low-alloy white cast iron. It can be concluded that the low-alloy white cast iron can be austempered, similar to ductile cast irons. Improved hardness and impact toughness values have been obtained in austempered low-alloy white cast iron.

In this study, we aimed to find the characteristic properties of the neat and the composite polydimethylsiloxane (PDMS) films. The composite films were prepared by adding 5 A and NaY zeolites and nano-TiO 2 to PDMS polymer matrix. In the preparation of the composite polymer films, the inorganic additives were added by 10 wt.-%. The structural and thermal characteristics of the prepared homogenous PDMS film and composite PDMS films were determined by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The glass transition temperature of the films was found by differential scanning calorimetry (DSC). Finally, the mechanical properties of the films were obtained through tensile tests. The effects of 5 A and NaY zeolites and TiO 2 on the neat PDMS films were investigated.

There is a trend towards smaller and smaller structures (nanostructures/ miniaturization) which is well-known in microelectronic, energy and semiconductor applications. Nanoengineering is expected to lead to significant improvements in the intrinsic properties of structures, e. g., in energy storage for supercapacitors. In this context, a deeper understanding of the growth mechanisms of the thinnest crystal layers is of crucial importance for the controlled growing of nanowhiskers with outstanding properties. In the present study, we consider a simple whisker growth model based on the surface energy (i. e., wettability) of the components and investigate the effect of the carbon interlayer deposited on a Si (111) wafer using the magnetron sputtering technique on the whisker formation during the subsequent molecular beam epitaxy process in the Si-C-Cu system. In the present study, the topographic holes in the carbon layer which are the preferred nucleation areas of whiskers were identified by a series of scanning tunneling microscopy analyses, and the natural hole density was statistically determined. Using atomic force microscopy, the surface roughness of the carbon layer was characterized. The results of our investigations indicate that there is a correlation between the hole density in the carbon layer and the density of Cu nanowhiskers. This may validate the supposition that the holes in the carbon layer are the preferred nucleation sites for whiskers – an effect that could be relevant for future works on the growth of nanowhiskers at predefined positions.

An asymmetric alumina ceramic membrane was prepared by secondary dip coating. The influence of different dispersants and dip coating parameters on the microstructure of the membrane separation layer was explored. Meanwhile, the pure water fluxes of the membranes with various microstructures were also studied. The results show that a separation layer with a defect-free thickness of 16.5 μ m and high surface flatness can be obtained when using polycarboxylate as a dispersant and twice dip coating within 2 s + 1 s and the pure water flux of an asymmetric membrane up to 1153 L × m -2 × h -1 × bar -1 . The present work provides a simple and effective method for controlling the morphology and permeation performance of an asymmetric alumina membrane.

In agricultural mechanization industry, different types of materials are assembled with each other to establish agricultural machine systems. However, the necessity of joining dissimilar materials used in the same machine system may cause some problems. Joining two different materials by welding and selecting the most appropriate weld metal (electrode) for this is a very difficult problem. The increasing importance of the economic factors in today’s industry requires both the use of dissimilar materials in agricultural mechanization and the production of longer-lasting agricultural machines, thus making it necessary to use dissimilar steels in agricultural mechanization systems. Therefore, it is important to apply a welding process to dissimilar steels used in agricultural mechanization. In this study, 30MnB5/S235 steel pairs were joined by the manual metal arc welding (MMAW) method using different covered electrodes. In order to determine the mechanical properties of the welded samples, hardness, bending, and impact tests were carried out. In addition, visual inspection to the weld seams, liquid penetrant testing, and metal-lographic examinations to determine the microstructural properties were conducted. As a result of the microstructure studies, structures such as grain boundary ferrite, Widmanstätten ferrite, acicular ferrite, bainite, and martensite were determined in the weld metal and HAZs. As a result of the hardness test, the highest hardness values were determined in HAZs on the side of 30MnB5 steel. As a result of the bending test, the highest mechanical properties were obtained in the weld seams made with basic flux-cored wire. As a result of the notch impact test, the highest mechanical properties were obtained in the weld seams made with basic flux-cored wire, after the base metals.

This study was carried out in two stages. In the first step, a numerical study was performed to verify the previous experimental study. In accordance with the previous experimental study data, single lap joints models were created using the ANSYS finite element analysis program. Then, nonlinear stress and failure analyses were performed by applying the failure loads obtained in the experimental study. The maximum stress theory was used to find finite element failure loads of the single lap joints models. As a result of the finite element analysis, an approximate 80 % agreement was found between experimental and numerical results. In the second step of the study, in order to increase the bond strength, different overlap end geometry models were produced and peel and shear stresses in the adhesive layer were compared according to the reference model. As a result of the analyses, significant strength increases were calculated according to the reference model. The strength increase in model 3 and model 5 was found to be 80 % and 67 %, respectively, relative to the reference model.

In this study, the effect of friction time on microstructure and weldability of AISI 1030 steel with nickel interlayer and high chromium white cast iron welded by the friction welding method were investigated experimentally. The weld joints were produced with 2000 rpm rotational speed, under 80 MPa friction pressure, 150 MPa forging pressure, for 8 s forging time and 8, 10 and 12 s friction times. After the friction welding process, the microstructures of the weld interfaces were analyzed by optical microscopy, scanning electron microscopy, energy dispersive spectrometry, elemental mapping and X-ray diffraction analysis. The results were lateron compared theoretically and experimentally. The increasing friction time led to high frictional heat input. The results indicated that friction time plays a vital role on the microstructure and weldability.

A finite element (FE) model is presented in this work that is used to analyze the effect of pitting corrosion on the CO 2 corrosion behavior of oil and gas pipeline welds. The FE model contains two parts, i. e., stress calculation of the welded joint using Abaqus software, and of the chemical reaction at the welded joint using COMSOL Multiphysics ® software. The effect of transportation pressure, pit depth and welding material on the CO 2 corrosion behavior of weld metal was investigated using the FE model. It turned out that the FE model is helpful to instruct the management and to assess the remaining service life prediction of pipelines in the oil and gas industry.

Most conventional optimization approaches are deterministic and based on the derivative information of a problem’s function. On the other hand, nature-inspired and evolution-based algorithms have a stochastic method for finding the optimal solution. They have become a more popular design and optimization tool, with a continually growing development of novel algorithms and new applications. Flexibility, easy implementation, and the capability to avoid local optima are significant advantages of these algorithms. In this study, shapes, and shape perturbation limits of a bracket part, which is used in aviation, have been set using the hypermorph tool. The objective function of the optimization problem is minimizing the volume, and the constraint is maximum von Mises stress on the structure. The grey wolf optimizer (GWO) and the moth-flame Optimizer (MFO) have been selected as nature-inspired evolution-based optimizers.

With the aim of leaving a smaller ecological footprint and to develop fuels which will change the energy needs of the future in a sustainable manner, the present study aims at investigating the corrosion phenomenon of brass using biodiesel fuel from cast-off cooking oil (CCO) in various blending ratios with commercial diesel (5 %, 10 % and 20 %) on brass. The mechanism of corrosion of brass in biodiesel has not been adequately investigated, and in the literature there is still a drop in the knowledge of the corrosion of brass from which many diesel engine parts are made. The corrosion rate of brass has been evaluated by mass loss and electrochemical methods. As a complementary technique, conductivity was monitored before and after each test. Surface morphology was examined by optical microscope. The surface morphology of brass samples in NaCl was coated in dark deposits that indicated corrosion. Some pitting was found in O99, and no significant change was found in oil-diesel blends. There is a positive correlation between the corrosivity and conductivity of the test media. The wettability studies also assisted in determining the non-corrosive nature of biodiesel.

The tensile strength, hardness and toughness of any materials are the most important mechanical properties in the selection of materials for varied industrial applications. In the development of aluminum based composite material, tensile strength and hardness were significantly improved by adding various ceramic reinforcement particles. However, toughness was reduced. In this research work, an attempt was made to enhance tensile strength, hardness and toughness simultaneously by using carbonized eggshell as reinforcement material developed via electromagnetic stir casting. The process parameters used in this study are the matrix pouring temperature, wt.-% of the reinforcement; preheat temperature, stirring current and stirring time. Response surface methodology (RSM) is used for conducting the experiment. The multi-objective optimization technique utility theory is employed to optimize the combined mechanical properties viz. tensile strength, hardness and toughness. Microstructure results show that at the optimum level of process parameters, eggshells are uniformly distributed. Confirmation tests are conducted to validate the experimental results. Experimental results revealed that at optimum process parameters, hardness and tensile strength are significantly improved without affecting the toughness property of the composite. The optimum level of process parameters to enhance all mechanical properties (tensile strength, hardness and toughness) were found to be a reinforced preheating temperature of about 448.32 °C, a stirring current of about 11.64 A, a stirring time of about 63.64 s, a maximum pouring temperature of about 800.24 °C and a percentage of eggshells of about 9.16 %. The novelty of this work lies in the fact that no attempt was made to optimize these electromagnetic process parameters. Corrosion loss, thermal expansion behavior and a wear test were investigated to observe the effect of adding eggshell at optimum electromagnetic stir casting parameters.

In this study, the impact behavior of sandwich panels of natural rubber-based syntactic foam cores with aluminum face sheets was investigated experimentally and with the help of finite element analysis (FEA). Syntactic foam cores were produced byadding glass bubbles (GB) to the natural rubber (NR). Natural rubber was dissolved at room temperature with chemical solvents mixed with glass bubbles at 10, 20, and 30 weight percentages. Very low density (~0.8 g × cm -3 ) and high compressible foams were obtained depending on the GB weight percentages. Aluminum face sheets and the NR/GB syntactic foam core developed were joined by adhesive bonding to produce sandwich beam specimens. The sandwich beams manufactured in this way were subjected to impact loading under three-point bending boundary conditions experimentally. The experimental results were compared with finite element simulation results under the same loading and boundary conditions. The damage mechanism of the sandwich panels devised were analyzed. According to the results, natural rubber containing an additive of 20 wt.-% GBs showed better impact resistance than the others.

In this study, aluminum Al6013 and copper (Cu) cylindrical bimetal was manufactured by means of an original production method. The optical microscope and scanning electron microscope (SEM) images of the bimetal material produced through this approach, semi-centrifugal compression, were used in microstructural investigations following which metallurgical transition zones were defined. Through an energy dispersive X-ray (EDX) analysis of the defined regions, the chemical content of the regions were determined. Micro hardness values of the regions were determined and comparisons were made with the chemical content and hardness values of the materials used in the bimetal production before the manufacturing process. In addition, the mechanical properties of the materials were compared by applying tensile tests to the bimetallic components Cu and Al6013 and to the bimetal material produced. In the light of the values obtained, the general properties of the bimetal material produced through this new approach were presented.

In this study, moisture dependent shear moduli in Scots pine ( Pinus sylvestris L.) wood were determined by a 45° off-axis (longitudinal, radial, and tangential) compression test and ultrasonic transverse wave propagation. Finite element modeling was performed to ascertain how the results agree with the numerical method. Ultrasonic transverse wave velocities on the LR, LT, and RT planes were decreased from 1347, 1323, and 589 m × s -1 to 1286, 1269, and 561 m × s -1 when relative humidity increased from 45 % to 85 % at a constant temperature of 20 ± 1 °C, respectively. The dynamic and static shear modulus on the LR, LT, and RT planes were decreased from 988, 953, and 189, and 966, 914, and 182 MPa to 927, 903, and 176, and 845, 784, and 154 MPa when relative humidity increased from 45 % to 85 % at a constant temperature of 20 ± 1 °C, respectively. Therefore, both velocity and modulus values at all principal axes and planes were decreased with an increase in moisture. Maximum (15.2 %) and minimum (2.3 %) differences between dynamic and the static shear modulus were observed for G LT at 85 % and G LR at 45 % relative humidity, respectively. Coefficients of determinations between the dynamic and static shear moduli were ranged from 0.68 (G LR at 65 % RH) to 0.97 (G LR at 85 % RH). Finite element analysis, only for 65 % RH values, was performed using Solid 45 element, and, according to results, load-deformation curves created by linear orthotropic material properties, are well-matched with the static curves.

This paper aims to investigate the effects of rice husk ash (RHA) on itself activity and its concrete performance at different preparation temperatures for which three temperatures of 650 °C, 800 °C, and 900 °C were considered. To find a reasonable particle size, the effect of the particle size of the RHA on the workability of concrete at various grinding times was studied. A series of experiments were carried out to study the characteristics of the RHA, including X-ray fluorescence, XRD, ESEM, and an activity test. The carbonation resistance and frost resistance of concrete incorporating RHA were also investigated, where 10 and 30 wt.-% of cement was considered. The results show that the surface area of the RHA first increases and then decreases with grinding time. When the RHA is ground for 30 min, its surface area is largest and the workability of its mixture is also best. The burning temperature has little effect on the amount of SiO 2 . Although the structure and activity of SiO 2 in RHA change at different burning temperatures, the performance of concrete incorporating RHA is higher than that of control concrete without RHA. With the same content of RHA, both carbonization resistance and frost resistance decrease with an increasing burning temperature of RHA. At the same burning temperature, both carbonization resistance and frost resistance increase with an increasing amount of RHA. Among all types of mixtures, the mixture incorporating 30 % RHA burned at 650 °C (i. e., RHA 650 ) yields the best performance.