Volume 64, Issue 11

The influences of the environmentally friendly sealing processes of cerium salt sealing and hydrothermal sealing on the electrochemical behavior of the anodic oxide film of an aluminum alloy were examined by accelerated corrosion of dry-wet alternate immersion corrosion tests, combined with the morphologies observation, chemical composition tests, and electrochemical tests. A severe corrosion environment with high temperature, high humidity, and high salt spray was adopted. The results of electrochemical characteristics show that cerium salt sealing affected the inner barrier layer of the film instead of the outer porous film. The higher impedance of the inner barrier layer is related to the reaction between cerium ions and cathodic reaction products of hydroxyl ions. Hydrothermal sealing, although had some good influence on both the porous layer and the barrier layer of the oxide film, corrosion inhibition on the whole cannot do better than that of cerium salt sealing in the early days. However, as the corrosion time went on, the hydrothermal sealing sample showed better durability.

Asymmetrical joints (joining of the plate with rod) were joined using traditional fusion welding processes. However, the usage of unsuitable filler wire tends to lower weld penetration over the material surface, which also results in the attainment of hot or solidification cracks over the weld surface. To overcome these issues, solid-state welding processes are preferable. This study investigates the rotary friction welding (RFW) of AISI 1018 low carbon steel plate with AISI 1020 low carbon steel rod of asymmetrical joints. The friction welding process parameters such as rotational speed were taken as variable, and other parameters like friction pressure, forging pressure, friction time, and forging time were kept constant in this investigation. The impact of rotational speed on macrostructure, microstructure, and mechanical characteristics of joints such as microhardness, tensile strength, and fractography studies was analyzed. The fractured surface of the tensile specimen was examined through a scanning electron microscope (SEM). The maximum tensile strength of the joint about 452 MPa was observed. Maximum hardness at the weld interface was perceived at about 252Hv. Increasing rotational speed tends to increase the strength of the asymmetrical steel joints in rotary friction welding.

2198-T8 Al–Li alloy was examined under different loading path. Uniaxial and multiaxial proportional and nonproportional loading tests were conducted to determine the material fatigue constant, and to study the multiaxial fatigue behavior, respectively. The multiaxial fatigue life was estimated by various criteria. The results show that, the torsional fatigue performance is better than the tension–compression fatigue performance. The fatigue life of nonproportional loading increases firstly and then decreases with the increase of phase difference from 0° to 90°. Shear Findley model and SWT model were modified by introducing shear damage parameters. The modified models provide fine results which are all within a factor of two.

Directed energy deposition (DED) has been in industrial use as a coating process for many years. Modern applications include the repair of existing components and additive manufacturing. The main advantages of DED are high deposition rates and low energy input. However, the process is influenced by a variety of parameters affecting the component quality. Artificial neural networks (ANNs) offer the possibility of mapping complex processes such as DED. They can serve as a tool for predicting optimal process parameters and quality characteristics. Previous research only refers to weld beads: a transferability to additively manufactured three-dimensional components has not been investigated. In the context of this work, an ANN is generated based on 86 weld beads. Quality categories (poor, medium, and good) are chosen as target variables to combine several quality features. The applicability of this categorization compared to conventional characteristics is discussed in detail. The ANN predicts the quality category of weld beads with an average accuracy of 81.5%. Two randomly generated parameter sets predicted as “good” by the network are then used to build tracks, coatings, walls, and cubes. It is shown that ANN trained with weld beads are suitable for complex parameter predictions in a limited way.

The deformation responses of AZ31B magnesium alloy under complex forming process are investigated experimentally through using the specially designed loading device consists of two metal blocks with two symmetrical bevelled ends. Based on digital image correlation analysis, the deformation process of specimen is clarified and the typical deformation modes are proposed. Results show that compression dominate the deformation response of specimen with smaller loading angle, while shear deformation becomes the major mode when the loading angle large enough. And an empirical formula is established for quantitative description the relationship between strain path and loading angle.

AISI 430 and HARDOX 450 grades were combined using tungsten inert gas double-sided welding process. Microstructural changes were evaluated with scanning electron microscope, energy dispersive spectrometry, electron back scatter diffraction, elemental mapping, X-ray diffraction analysis. Mechanical diffenrences of welded alloys were determined by tensile, notch impact and microhardness tests. Failure surfaces of tensile samples were examined by SEM. The maximum tensile strength was 513.59 MPa and the impact energy was 77 J at welding speed of 0.01 m min −1 at current of 475 A. The lowest hardness was determined in HAZ due to excessive grain size. Failure exhibited brittle fracture and cleavage planes.

Composite joints have been commonly used in many industries such as aviation, aerospace, and automotive due to their advantages of being light and durable. Internal stresses may occur especially during the service life of these materials and decrease the load-carrying capacity of the joints. In this study, high density polyethylene (HDPE) and glass fiber reinforced polypropylene composite panels are used resorting to different combinations by using hot-pressing method as a single lap joint, and their mechanical properties are investigated under different temperatures, experimentally. Tensile tests were carried out at different temperatures in order to examine the temperature effect on load-carrying capacity of joints. Different bonding types of composites were compared to obtain the optimal joint configurations. The effect of low velocity impact on the failure response of the joints at impact energy levels of 5 and 10 J is also evaluated. From the tensile tests after impact treatment, it was concluded that transverse impact significantly decreased the load-carrying capacity of the single lap thermoplastic joints. Based upon the experimental results, it was concluded that HDPE–HDPE joints demonstrated higher tensile failure loads at 50 °C after transverse impact. Moreover, the tensile strength of all types of configurations decreased with increasing temperature.

Diaphragm spring is a critical part of a clutch system because it affects the release bearing load characteristics directly and that determines the quality of disengagement. Bearing load provides required clamping for coupling however it may vary significantly during the engagement/disengagement process. A significant drop in bearing load may be experienced especially for high engine velocities for certain bearing displacement due to centrifugal forces occurring on the fingertips of diaphragm springs. The falling in release bearing load is undesirable for comfortable driving and clutch performance. This problem has not been addressed clearly in technical literature. In this study, the diaphragm spring for a C-segment passenger car is optimized using a differential evolutionary algorithm, and an optimized diaphragm was manufactured for testing. The load-bearing characteristics of the optimized diaphragm were compared with those of the currently available diaphragm spring. Loss of bearing load occurring in high-speed rotations was significantly reduced for the optimized diaphragm. Parameters influencing the performance were identified using parameter influence analysis, and a robust disengagement behavior was actualized using the optimization process.

In this study, the effect of heat treatment applied at various temperatures on the properties of plasma arc welded TRIP800 steel has been examined extensively. For this purpose, the low temperature heat treatment was carried out at −50, −20, and 0 °C for 2 h on a set of welded samples. Moreover, the heat treatment process was also applied for 2 h at various temperatures (i.e., 100, 200, 300, 400, 500, 600, 800, and 1000 °C) for another group of plasma arc welded TRIP800 steels. In addition, the properties of a set of samples without any heat treatment were determined in as-welded condition for a comparison. The mechanical properties of all samples were determined, and microstructures of samples were evaluated. As a result, the low temperature heat treatment applied at the specified temperatures did not have a significant effect on the ultimate tensile strength, and ductility of the joint but affected the yield strength positively. Besides, the ultimate tensile strength of heat treated samples also diminished with increasing processing temperature. It was found that the yield strength of the heat treatment applied samples showed an increase up to 500 °C, while the samples tested at 500 and 600 °C showed pronounced yielding behavior.

In this study, boriding of DIN Ck 45 steel, which is hard chrome plated after induction hardening, is used as a linear shaft in 3D printers. The boriding treatment, which was carried out by the pack-boriding method, was carried out in an atmosphere-controlled furnace at 1273 K for 2 h. The thickness, morphology, hardness, and chemical composition of the boride layer formed on the sample surface as a result of the boriding process using Ekabor 2 boriding agent were examined and compared with the un-borided sample. The microstructure images were obtained with a digital camera integrated into an optical microscope, and these images were analyzed in detail with the help of an image analysis program. After the optical microscope examinations were completed, point EDX analyzes were performed on the image obtained with the help of SEM. As a result of EDX analysis, it was determined that the layer formed on the material surface was only chromium boride formed by the interaction of chromium and boron element. Finally, the hardness measurements of the borided sample were carried out with the help of Vickers indenter and then differences were compared with the un-borided sample.

Material type and part deposition orientation are two important concerns in additive manufacturing. Additive manufacturing methods utilized by the industry are generally based on polylactic acid (PLA) or acrylonitrile butadiene styrene (ABS) materials using the fused deposition modelling (FDM) method. However, in present commercial applications, besides extensive use of PLA/ABS, their low strength has emerged as their biggest disadvantage. However, polyetherimide (PEI)/ULTEM 1010 parts represent high-performance engineering thermoplastics and offer superior mechanical properties with high thermal stability. On the other hand, selection of an appropriate raster angle orientation for single- and multi-oriented layers is also of considerable interest. A comprehensive study has been conducted herein on the building of a part using the FDM method using PEI/ULTEM 1010, and attempts have been made to identify the effects of raster angle in single- (0°, 30°, 45°, 60°, 90°) and multi-oriented (0/90°, 30°/−60°, 45°/−45°, 0°/90°/45°/−45°) layers. PEI specimens were manufactured via 3D printer, and the mechanical behaviour (tensile, bending and hardness) of the printed parts was correlated with their structures. Morphological properties of tensile fracture surface of 3D printed samples were analysed using scanning electron microscopy (SEM). Analysis indicated that a 0° part deposition orientation offers optimal mechanical properties because of the bonding structure.

Welding is the most commonly used joining process in the industry. Generally, weld zone consists of three different regions such as base metal, heat-affected zone (HAZ) and weld metal (WM). Microstructure of HAZ and WM changes due to the heat effects after the welding process. These effects cause changes in mechanical properties such as Young modulus, tensile strength and hardness in weld zone. The aim of this paper is to identify the mechanical properties of weld zone by uni-axial tensile test, nanoindentation test and hardness test. For this aim, quenched and tempered steel plates were chosen as a test material having high strength. These plates were welded together by flux-cored arc welding method. To determine the effect of weld pass number on the mechanical properties, the weld was completed in single and multi-pass (MP) butt welds separately. For experiments, tensile test specimens were cut by plasma cutting method according to related standard on welded plates. These specimens were subjected to three different post weld heat treatments (PWHT) such as 200 °C, 300 °C and 400 °C to evaluate the hardness change in HAZ. The effect of weld-pass number and PWHT on mechanical properties such as Young modulus, tensile strength and hardness were obtained from WM and HAZ by uni-axial tensile test and nanoindentation test and compared to each other. The yield and ultimate tensile strength of weld zone of welded tensile test specimens (WTTS)-2 is lower than WTTS-1 due to MP welding process. Furthermore, the strain behaviour of weld zone is not affected by PWHT significantly.

It is known that the strain rate affects significantly the mechanical properties of the engineering materials. The aim of this study is to investigate the effect of the cross-head speed on the mechanical properties of acrylate and methacrylate-based oligomer/monomer materials of the specimens produced by Stereolithography (SLA) printer. The characteristic mechanical properties of materials, such as modulus of elasticity, Poisson’s ratio, and the ultimate strength depending on low strain rate levels were explored. The fractured surfaces of the tensile test specimens were examined by Scanning Electron Microscopy (SEM). Based on the experimental results, it is concluded the mechanical properties of the photosensitive resins are quite sensitive to the tensile test speeds.

High power applications at high speed create contact problems, increase heat sink values and transmission error (TE) during gear meshing. Hence, analyzing the gear mesh including helix angle effect, the optimization in terms of contact pressure and the transmission error reduction are all crucial for high-speed applications. In this study, meshing characteristics including helix angle based on different approaches, optimization of spur gears pairs in terms of the transmission error and contact stresses obtained from improved analytical method besides transmission design tools are all investigated for high-speed aerospace applications. Results reveal that significant transmission error reduction could be achieved by applying tip relief starting from the highest-point of single tooth contact for spur gears in aerospace applications. Hence, the need for higher contact ratio by helix angle inclusion for smoother transmission could be compensated by using tip-relief modified spur gears in gearbox since the heat sink values also need to be minimized by using relatively lower contact ratio. Results obtained from the improved analytical method by directly considering gear geometry including gear foundation effects based on direct deformation–summation approach are found in between AGMA (American Gear Manufacturers Association) standard and ISO (International Organization for Standardization) standard results.