Volume 66, Issue 5

Bellow joints are frequently used in hydraulic lines, constructions, and various areas such as nuclear stations to absorb the energy caused by flow and external forces, provide flexibility to the lines, and prevent damages such as cracking and deterioration in the flow lines. There exist various types of bellow joints (e.g., axial type, gimbal type, and hinge type) that allow axial, lateral, and angular movements. Bellow joints that assist thrust vector control in liquid propellant rocket engines prevent the hydraulic lines from being damaged during the orientation movements of the missile. While providing this flexibility to the lines in rocket engines, they create additional force against the linear actuators that move the liquid motor nozzle. This additional force causes the need for larger actuators, resulting in more weight and volume. In this study, design optimization of the bellow joint used in liquid propellant rocket engines is conducted to minimize the force transferred to the actuators by minimizing the bending moment developed in the bellow joint. It is found that the bending moment developed in the bellow joint could be reduced by a significant rate of 75 % without compromising the structural integrity of the bellow joint.

This study investigated the microstructure and mechanical properties of the recycled Ti6Al4V alloy produced using the waste chips vacuum arc melting (VAM) process. The waste chips were cleaned to remove machining residues before VAM and dried in the oven. The dried and compressed chip compacts are vacuum arc melted and hot rolled. Microstructural characterization was performed by using an optical microscope, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analysis. Mechanical properties were determined by tensile and hardness tests. The microstructures of recycled Ti6Al4V alloy, which produced the VAM process, consist of acicular structures due to rapid solidification. After hot rolling from 950 °C, the elongated α grains and transformed β grains consisting of fine acicular α phase were observed. The recycled Ti6Al4V alloy by hot rolling after VAM exhibited very low total elongation compared to the as-received Ti6Al4V alloy. While a micro dimples ductile fracture was observed on the fracture surfaces of the as-received Ti6Al4V alloy after the tensile test, a brittle fracture surface was observed in the recycled Ti6Al4V alloy samples after VAM + hot rolling due to the coarse α and β grain structure after cooling in the air after hot rolling.

In this study, two high-temperature shape memory alloys (HTSMAs) of CuAlV with unprecedented chemical compositions were fabricated using the arc melting technique, followed by traditional ice-brine water quenching after the melting process. To characterize the shape memory properties and structure of the alloys, a series of tests including differential calorimetry (DSC and DTA), EDS, optical microscopy, and XRD were conducted. The DSC tests, performed at different heating and cooling rates, demonstrated highly stable reversible martensitic phase transformation peaks at high temperatures, which were also confirmed by the results of DTA tests. Microstructural XRD and optical microscopy tests were conducted at room temperature, revealing the martensitic structure of the alloys in both cases. Based on all the results, the effects of different minor amounts of vanadium additives directly on the CuAlV alloy were discussed.

Coatings deposition using different materials and various techniques are a viable method to improve the surface properties of alloys, especially the surface strength with improved tribological properties. In this study, a series of Co-based reinforced composite coatings containing different ratios of WC–CoCr–Ni particles were fabricated by laser cladding onto the surface of an AISI 904L stainless steel substrate. The main goal of this experimental work was to determine the influence of the WC particle addition on the structure and properties of the obtained Co composite coating in terms of improving the sliding wear resistance without negative influence the corrosion resistance in chloride media. The effect of the WC particles onto the microstructure, phase composition, microhardness, wear and corrosion properties, was investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) in association with the evolution of the friction coefficient and that of the polarization curves, respectively. The achieved results have shown that the new phase composition, especially developed due to the remelting of the WC phase, led to an improvement of the wear resistance. No significant changes were recorded after the electrochemical tests evaluation.

The present research work is focused on analyzing the tribological and corrosion impacts of introducing a new metal/bioceramic (Ti/HA) compound into the matrix of the Mg–3Zn alloy. The hybrid composites were developed using the squeeze casting method. The density, microhardness, and microstructure of the developed composite materials were examined. A pin-on-disk tribology meter was used to conduct the tribological study under a phosphate-buffered saline (PBS) lubricating medium. Studies on electrochemical corrosion were carried out in the PBS medium. Incorporating hybrid Ti/HA particles into the Mg–3Zn alloy matrix significantly increased the density and microhardness of the composites. Optical microscopy demonstrates a refined grain size and uniform distribution of reinforced particles, showcasing improved structural integrity. Scanning electron microscopy analysis further confirms the α-Mg and β-Mg–Zn phases. According to the findings of wear tests, the Ti/HA inclusion in the Mg–3Zn (MZ0) matrix increased the resistance to wear behavior. Abrasion, delamination, oxide layer formation, and severe delamination features were observed at the worn surfaces. Abrasive wear happened along with all other wear mechanisms and served as a wear initiator. Potentiodynamic polarization experiments revealed that the corrosion resistance of hybrid composites was increased with the inclusion of 1.5 % HA.

In this study the effect of T6 heat treatment, two-step aging treatment and ultrasonic impact peening on the exfoliation corrosion behavior of welded EN AW 7020 was investigated. Exfoliation tests were performed according to the ASTM G34-01 standard. As expected, as a result of the tests, the base material region of all three samples were showed better corrosion resistance than the heat-affected region. Ultrasonic impact peening and two-step aging treatment was observed that improved EXCO sensitivity in the weld area. When sorting was made by considering the resistance to corrosion of the heat affected zone of the samples, it was observed that the best resistance was shown by the sample with two-step aging treatment, and the worst resistance was shown by the sample with T6 heat treatment.

Thin-walled structures are one of the important safety components used in vehicles. They are placed in the front parts of the vehicles to minimize the impacts that occur in the event of a collision, and they absorb the impact force by changing shape in the event of a collision. Crash boxes have high-impact absorption, low weight, and low-cost expectations. In the design of crash boxes, thin-walled structures are preferred due to their high deformation capability. In this study, the additive manufacturing method was used to produce thin-walled structures. Thin-walled structures were produced by additive manufacturing methods using PLA and ABS materials. The manufactured crash boxes were tested using an impact test. In the experimental results, the energy absorption ability of the crash boxes produced from PLA and ABS materials was examined, and high fragility was observed. The experimental results were verified by finite element analysis of the crash boxes made using PLA and ABS materials.

This study investigates the effect of printing parameters on the acoustic performance of specimens produced using 3D printing technology. The specimens were fabricated with square and hexagonal cell shapes with 10, 20, 30, and 50 % infill ratios from acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) materials. The sound absorption coefficient and sound transmission loss results of the samples were measured with an impedance tube at 1/3 octave band values in the range of 500–6400 Hz. The highest sound absorption coefficient results were determined for cylindrical samples with a square internal structure made of ABS material with a 50 % infill ratio in the frequency range of 2500–3500 Hz. The sound transmission loss values of the samples vary between approximately 13 and 58 dB at 1/3 octave band values in the range of 500 and 6300 Hz. The highest sound transmission loss values were determined in the sample produced of PLA with a square cell shape at a 30 % infill ratio. It was concluded that different geometric shapes, materials, and infill ratios affect the acoustic performance of parts produced by 3D printing technology.

This study deals with the development of a load-converting device designed for measuring the direct tensile strength of the concrete. In this regard, a new testing technique based on a novel testing device and modified cylindrical (Ø 100 × 200) molds for the preparation of concrete samples is explained. The embedded rod method was adopted to transmit the uniaxial tensile load to the specimens using the universal compression machine and the current converting device. In order to examine the reliability of the suggested test method, a comparison with indirect tensile methods (splitting and three-point loading flexural tests) was made. The results show that the tensile strength of the tested specimens is lower for the direct tensile test obtained by the proposed test setup than for the flexural test and closer to the strength results obtained from the splitting test. As expected, all the specimens tested using the introduced test method demonstrated a sudden and unique fracture in the middle portion. Additionally, no slippage of embedded bars was noticed during the test.

The one-stage YOLOv5 steel surface defect detection has issues such as slow operation speed, loss of defect location and semantic information of small targets, and inadequate extraction of defect features. This study proposed a defect detection algorithm with improved YOLOv5 to solve these issues. The proposed algorithm used the slim-neck layer built by three new modules instead of the neck layer in YOLOv5s to achieve a lightweight network model. In addition, the spatial perception self-attention mechanism was introduced to enhance the feature extraction capability of the initial convolutional layer without limiting the input size. The improved Atrous Spatial Pyramid Pooling was added to expand the perceptual field and capture multiscale contextual information while preventing local information loss and enhancing the relevance of long-range information. The experimental results showed that the improved YOLOv5 algorithm has a reduced model volume, significantly higher detection accuracy and speed than the traditional algorithm, and the ability to detect steel surface defects quickly and accurately.

Ti6Al4V alloy is a commonly used α + β alloy among titanium alloys. In this study, in order to improve the oxidation resistance of the Ti6Al4V alloy, Ti–Al – based aluminum coating was deposited to the surface by the pack cementation method. The aluminizing process was carried out in an open atmosphere oven at 700 °C for 4 and 6 h. It has been observed that the coating layer thickness varies between 13 and 17 µm depending on the duration of cementation process. From XRD analysis, it has been detected the TiAl 3 , TiAl 2 , and TiAl phases on the coating layer. Aluminum coated and untreated Ti6Al4V alloys were subjected to oxidation tests at 800, 850, and 900 °C for 4, 20, and 40 h. The obtained nonlinear weight gain characteristic has been modeled to determine the coating status of the samples. It was determined that the highest weight gain was in the untreated sample. Using the provided model, samples were classified in terms of coating condition by systematic approach based on weight gain profile versus time. Oxidation tests also supported with DTA and TG analyses.

Ni-Hard 4, also known as white cast iron, is widely used in many applications that demand high mechanical strength. This material is recognized for its ability to withstand challenging conditions. In this study, surface modification processes, particularly boriding, were carried out on the material. Boriding is considered an effective process for enhancing the mechanical strength of a surface. While there are various methods for performing boriding, the pack-boriding method was chosen for this study. This method was applied in a typical heat treatment furnace. Ni-Hard 4 specimens were subjected to different combinations of temperature (1000–1200 °C) and 4 h duration, resulting in a total of three distinct samples. Subsequently, the microstructure, hardness, and chemical composition of the boride layers formed on the material’s surface were meticulously examined. As a result of the detailed analysis, it was determined that if the boriding process was carried out in a furnace without controlled atmosphere, high temperature oxidation started on the surface of Ni-Hard 4, and in this case it increased in parallel with the increase in temperature.

The use of composite materials, which are more economical and have better material properties, has become widespread in the industry lately. The glass fiber reinforced polyester composite materials constitute majority of composite materials produced in industry. Wear reduces working life of machine parts, affects their functions, and causes undesired deterioration, resulting in part separation over the contact surface. The machine parts produced from glass fiber reinforced polyester composite materials wear out because of exposure to dry friction and fluid film lubrication under different operating conditions. In this study, wear behaviours of glass fiber reinforced polyester composite materials under dry friction and fluid film lubrication conditions were investigated. The various results were obtained with this study. The wear resistances of samples in dry friction and fluid film lubrication conditions are like each other. The use of glass fiber, glass bead and plasticizer tensile additive in glass fiber reinforced polyester composite specimens is effective in improving the wear resistance of specimens.

X-rays have many uses in screening and materials characterization applications. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis are among them. From the XRD data, a crystal structure can be determined by analysis of the XRD pattern, intensity, and positions of the peaks. Information about the crystallographic space group, lattice parameters, preferred orientation, and crystallite size can be derived. XPS examines the surface chemical state of a sample. This review will focus exclusively on MXene compounds and their analysis using XRD and XPS. MXene are layered compounds with a strong potential for application in energy storage. Since MXenes are two-dimensional (2D) transition metal carbides and nitride, the material exhibit signals indicating the presence of specific transition elements, 1s carbon, and 1s oxygen. Additionally, there is a possibility of detecting an element from group 13 or 14 of the periodic table, such as aluminum, nitrogen, or fluorine. A comprehensive study based on XRD and XPS analytical techniques of 2-dimensional electrode materials may provide advancement in the field of energy storage. MXene especially deserve attention due to their remarkable structural and electrochemical characteristics, such as conductivity, topological, and surface area, which attracted numerous researchers worldwide.