Band 63, Heft 9

To investigate the influence of post-weld heat treatment on the microstructure and corrosion properties of super duplex stainless steel welded joints, multi-layer multi-pass welding of 2507 super duplex stainless steel by tungsten argon arc welding was performed using an ER2594 welding wire. The microstructures of the welded joints before and after post-weld heat treatment at 1150 °C, 1170 °C and 1190 °C were observed, and the mechanical and corrosion properties were tested. The post-weld heat treatment changed the austenite content and morphology of the welded joint and improved the corrosion resistance of different parts of the weld metal. The choice of various solution heat treatment temperatures affected the change in austenite content in the weld zone and the degree of diffusion and homogenization of the alloy elements. After post-weld heat treatment at 1170 °C, the two-phase ratios in each area of the weld were the most suitable and uniform, and the overall mechanical and corrosion properties of the joint were more uniform.

In this study, the effect of change of notch type on non-linear buckling behavior in composite plates was investigated experimentally and numerically. The composite plate is produced by applying the vacuum infusion method using carbon and aramid hybrid woven fabric and epoxy. Primarily, in the composite plates, a circular hole in the middle, a U single edge notch and semicircle double edge notches are formed. The specimens were subjected to buckling tests, being placed on their two edges, while the others were free. Afterwards, the load displacement graphs of the plates under pressure load were obtained experimentally for the behavior before and after buckling. In the numerical study, non-linear buckling analysis was performed using the finite element method. As a result, experimental and numerical buckling behaviors were obtained in accordance with each other. Since the net cross section bearing the pressure load is equal for all notch types, an effective difference between the maximum damage loads has not been achieved. So, the variation of notch type does not change the load displacement behavior characteristics of the plates after buckling. However, due to the unsymmetrical geometry in U notched plates, an uneven change in horizontal displacements along the width of the plate was achieved. The maximum stress concentration formed around the notch increased after buckling with the increase of displacement in vertical direction.

The effect of chromic acid anodizing (CAA) surface treatment on 7050 T7451 aluminum alloy was presented in this study in terms of fatigue behavior. CAA is a treatment against corrosion by producing aluminum oxide layer (Al 2 O 3 ) at the surface. However, fatigue performance of 7050 T7451 is affected by the coating. In this study, eight different CAA processes were examined with regard to etching stage of pre-treatments by using an alkaline etchant and/or acid etchants with various immersion times. Optical microscopic examinations were applied in order to determine pitting characteristics for the selection of CAA process parameters before fatigue tests. A CAA process was selected among eight processes in terms of pitting characteristics in order to apply fatigue specimens. Four fatigue test groups were determined to investigate bare condition of 7050 T7451 and sub-stages of the CAA particularly. Constant amplitude axial fatigue tests were conducted on specimens at 91 Hz at stress ratio (R) -1 until run-out criteria, which was 10 6 cycles. Fatigue life reduction was determined due to pretreatments of CAA. Fracture surfaces of the specimens were examined by scanning electron microscope (SEM) to investigate morphology and crack initiation sites.

Composite materials are widely used in the marine industry. The marine environment, on the other hand, has a significant impact on the strength of composite materials. The tensile strength is adversely affected because the matrix material absorbs water. In this study, the effect of orientation, number of layers and different mediums over time on the tensile strength of the woven carbon fiber reinforced epoxy composite material was investigated experimentally from a comprehensive perspective. The findings of the experiments were subjected to variance analysis. The repeated tests and cross-results of the experimental parameters were found to be compatible with each other. Seawater reduces the tensile strength of composite materials in any case. The tensile strength increased with increasing the number of layers. However, it has been observed that the seawater medium reduces strength when the number of layers increases. At the same time, as orientation angle rises, the seawater medium’s negative effect on strength rises.

As the main contribution of the present study, an I-shaped joining element, which allows the plates used in large composite structures to be joined butt-to-butt, has been improved in terms of load capabilities. It is desirable that the joining zones of composite plates not be visible according to the design of composite structures and the requirements for the desired use in particular. In other words, it is not desirable to create any surfaces that would cause protrusions in the joining zones. The only joining technique that fulfils this condition is the butt joint. Generally, butt joints are performed by bonding. With this technique, it is possible to make a more durable mechanical butt joint using an I-shaped joining element. In this way, instead of bonding butt joints, stronger non-bonding or bonding mechanical butt joints can also be achieved. In this study, the geometric changes in the shape of an I-shaped joining element used in mechanical butt joints and the changes in load-carrying capabilities have been studied experimentally and numerically. Experiments were carried out with tensile, three-point bending and four-point bending tests. The experimental specimens and I-shaped joining elements were cut using a water jet machine. Abaqus finite element analysis software was used for numerical analysis. The numerical data obtained in the study were found to be consistent with the experimental data. The load-carrying capabilities of the joining elements of different geometric shapes were studied numerically and experimentally, and it was found that the ideal element was the joining element with a 60° angle.

International organizations such as the World Health Organization (WHO) and the International Labor Organization (ILO) have called for an end to the use of asbestos and its derivatives in all sectors, primarily due to the negative effects on human and environmental health. For this reason, manufacturing and use of asbestos linings are also prohibited in most developed countries. For this purpose, there are many studies in the literature on the development and research of nonasbestos linings. In the literature, topics such as material content, production, cost, braking performances and mechanical properties of composite linings are commonly encountered. With the technology in the developing world, the working conditions of vehicle elements are getting more difficult. For this reason, during braking, the amount of energy required to be damped against the unit area in the pad surfaces increases, and since the lining surface areas get smaller, the operating temperatures exceed the limits of the material components. Under these conditions, the design of the lining material content is extremely important, taking into account parameters such as load and operating conditions, in order to slow down or stop the vehicle safely. In this study, the braking performance, mechanical and tribological properties of the samples obtained from a number of production processes such as mixing, pre-shaping and pressing of the materials by altering the particle sizes (50 μ m, 75 μ m and 125 μ m) of the filler and friction materials used together with powdered alumina (Al 2 O 3 ) were investigated. The most suitable parameters were determined as lining material for the samples obtained.

AA5754Al alloy is widely used in industry. However, as in the case of all Al alloys, the 5xxx series Al alloys cannot be easily joined through fusion welding techniques. To address this problem, in this study, the effect of double-sided friction stir welding at various tool rotational speeds (450, 710, and 900 rpm), feeding rates (40, 50, and 80 mm × min -1 ), and tool tilt angles (0°, 1°, 2°) on the welding parameters and mechanical and microstructural characteristics of AA5754 Al alloy was determined. Tensile strength tests and microhardness tests were performed to examine the mechanical properties of the welded specimens. The microstructures of the welded zone were examined by obtaining optical microscopy and scanning electron microscopy images. The tensile test results indicated that the specimens exhibited the highest welding performance of 95.17 % at a tool rotational speed, feed rate, and tool tilt angle of 450 rpm, 50 mm × min -1 and 1°, respectively.

The tribological properties of aluminum based Al-25Zn-1Mg alloy was experimentally investigated in an MSc thesis, and the results are presented in this study. To this purpose, Al-25Zn-1Mg was commercially produced by casting. The prepared samples were divided into seven groups: no-process, solution treatment, and artificial aging for 1, 3, 6, 12 and 24 hours. Aged and untreated samples were subjected to tribological experiments under conditions of dry friction under 5 N and 10 N loads at speed of 200 rpm, 400 rpm and 800 rpm for a distance of 500 m. As a result of the tests, it was found that hardness increases in all samples depending on the aging process. It was also found that when the test speed was kept constant, the coefficient of friction increased with increasing load.

This work shows the results of research of the fine and dislocation structure of the transition layer of 18CrNi3Mo low-carbon steel after the influence of electrolytic plasma. Conducted research has shown that the modified steel layer, as a result of carbonitriding, was multiphase. Quantitative estimates were made for carbonitride М 23 (С,N) 6 in various morphological components of α -martensite and on average by material in the transition layer of nitro-cemented steel. It was established that α -phase is tempered martensite after nitrocementation. Released martensite is represented by batch, or lath and lamellar low-temperature and high-temperature martensite. Inside the tempered martensitic crystals, lamellar cementite precipitates are simultaneously present, and residual austenite is found along the boundaries of the martensitic rails and plates of low-temperature martensite. It was determined that inside the crystals of all morphological components of α -martensite there are particles of carbonitride М 23 (С,N) 6 .

The objective of the present experimental work is to investigate the influence of subsurface roughness on the friction and wear performance of high-temperature ball bearing. Bearings, which are used in high-temperature applications, are affected by several operating conditions. Some factors under high-temperature conditions such as short grease life, thin-film thickness at low speed, and insufficient internal clearance can drastically reduce bearing service life due to an increase in surface friction. For this reason, rolling contact bearings are coated with molybdenum disulfide. Before the molybdenum disulfide (MoS 2 ) coating, phosphatization is applied to the bearings. Because the phosphate layer is micro-porous, it assures that molybdenum disulfide is entrapped in the interstitials between the phosphates. Also, phosphate coating provides a much larger surface area for the lubricant to attach to. In this study, several process steps, sandblasting, manganese phosphate coating, molybdenum disulfide coating, friction moment testing, wear testing, wear depth measurement, SEM, and XRD analyses were carried out. Wear tests and friction moment tests were applied to the rings of bearings of varied raceway roughness. This process ultimately provides molybdenum disulfide coated bearings optimum raceway roughness parameters for good wear resistance and optimum boundary lubrication.

The protection of historic buildings has drawn increasing attention and usually requires a sound nondestructive testing (NDT) technique. This paper first describes the significance of and the status on the protection of historic structures followed by a summary of common damage and repair measures for such structures. Lastly, the principles, characteristics, and applications of NDT techniques for historic wooden and masonry structures, including ultra-CT testing, stress wave testing, micro-drilling resistance meter, radar detection, and X-ray diffraction, are described and compared. This study concludes by providing a guide for studying the structural damage of historic structures and for the selection of a detection technique.

Recycling rubber aggregates from used grinded tires is a behavior of environmental protection. By performing cyclic flexural tests, this paper explores the effect of rubber aggregate content on the crack propagation of notched concrete beams containing waste rubber aggregates. The crack mouth opening displacement is tested. The acoustic emission technique is applied to detect the damage in the fracture process zone. The crack propagation is evaluated using the critical value of the mode I stress intensity factor. It was found that the crack length and stress intensity factor decrease with the increasing of rubber aggregates content. The crack length and stress intensity factor at failure under constant cyclic loading are larger than those at corresponding post-peak load level. It was observed that the damage evolution curves under cyclic envelope loading can be divided into three stages: initial-quick-stable stages. And they are S-shaped, quick-stable-accelerated curves under constant cyclic loading. Rubber aggregate reduces the acoustic emission activities in concrete specimens. Accumulations of acoustic emission hits, acoustic emission counts and acoustic emission energy are found in accordance with the damage evolution of concrete beam. The relation between damage and accumulative acoustic emission hits is quantified by fitting experimental data. The fitting curves agree well with test results.

Construction materials used in arid zones in Algeria are mainly concrete and clay bricks. These materials are not suitable for this climate as they have poor insulating properties. In order to improve thermal comfort in buildings and to save energy, materials used in construction must be good insulators while having an acceptable mechanical strength. New extruded clay bricks have been developed by incorporating date palm fibers into the clay matrix. These are considered renewable and are abundant agricultural waste generated by date palm trees each year without exploitation. Starting from the composition usually used by the local brickyard, seven compositions were tested, with clay/fiber ratios from 80 %/0 % to 68 %/12 %, by considering as a constant the sum of the masses (clay and fiber), with the percentage of dune sand maintained as equal to 20 wt.-%. From experiment tests it was observed that for a composition with 68 wt.-% clay, 20 wt.-% dune sand and 12 wt.-% fiber, the bricks prepared were light weight, had good thermal properties and met compressive strength requirements. For this composition the weight reduction exceeded 23 % for an energy saving impact of more than 44 % in a dry state.

Magnetic abrasive finishing (MAF), an unconventional process, enhances the surface finish of a material. The current research focuses on its use with SS310s. The finite element analysis (FEA) result shows the effect of control parameters on the magnetic flux density. In FEA analysis, it was decided to maintain an air gap of 1.5-2 mm and a voltage of 10-20 V. A response surface methodology (RSM) desirability function is used to identify the optimal process parameters. Experiments are conducted for optimizing the process parameters like voltage, rotational speed, machining gap, mixing ratio, and mesh number to enhance the material removal rate (MRR) and surface roughness (Ra). A series of 62 experiments are conducted using optimized process parameters at different levels. Moreover, analysis of variance (ANOVA) is used to identify the percentage contribution of each process parameter in % Δ Ra and MRR. From this, the mesh number of the abrasives plays an important role in the finishing process owing to the increased number of cutting edges and because of the uniform normal force (Fn) distribution. The optical microscopic image result and the wear test confirms that the surface finish of SS310s has been improved using MAF.