Volume 64, Issue 2

Both processes, laser beam welding and electron beam welding, rely on the deep penetration process with the typical metal vapour capillary to achieve welds with in-creasing weld-in depths. With both processes, the capillary is the result of a highly dynamic equilibrium of various opposing forces and influences. To increase the understanding of the fluid-dynamic processes inside and around the vapour capillary, methods are needed for the supervision of the process that can deliver geometrical information with high spatial and temporal resolution and especially from the deeper capillary regions. Gaining this insight will allow the implementation of highly dynamic processes in future capillary models as well as the extension of process windows of the beam welding processes.

This research investigated the effects of adding rhenium and ruthenium with various contents to new modified nickel-based superalloys, which were prepared and cast using a vacuum arc melting process. Heat treatment processes were then carried out. The size, circularity and the area fraction of the gamma prime phase were characterized via scanning electron microscopy after solution treatment, precipitation aging and long-term heating processes. The addition of ruthenium seems to provide a stronger effect than adding rhenium by increasing the area fraction of the gamma prime phase after precipitation aging. Furthermore, rhenium and/or ruthenium additions maintain the precipitation of the gamma prime particles in a cubic shape. For phase stability analyses, the alloys were subsequently heated at 1173 K in intervals up to 1080 ks. The study showed that the coarsening rate of γ ′ particles can be significantly retarded with the addition of rhenium and/or ruthenium, and topologically close-packed phase can occur with excessive rhenium addition. In addition, the highest addition of ruthenium content in this study strongly exhibited high gamma prime phase stability. Thus, increasing the content of ruthenium and decreasing the content of rhenium can inhibit the formation of the topologically close-packed phase.

Cu\Fe–Cr–C metal matrix composites (MMCs) were produced with a reinforcer addition of 6, 9, 12, 15, and 18 wt% Fe–Cr–C by powder metallurgy. The effects of sintering temperatures on Cu-based Fe–Cr–C-reinforced composites were studied using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and hardness test. The electrical conductivity and tensile and fatigue strengths of samples were investigated by the conductivity meter and the tensile and fatigue testing machine. The interface microstructure between Fe–Cr–C and Cu particulates at 1000 °C showed a significant difference. The increase in tensile strength, hardness, and fatigue life gave a proportional change with an increase in Fe–Cr–C particulate vol%. The precipitated carbides and intermetallic compositions reduced electrical resistivity depending on the sintering temperature.

Polyethylene is a very common liner material for type IV pressure vessels due to its good toughness and easy processing. The property profile of the polymer can be improved by cross-linking thereby changing the nature of the polymer from thermoplastic toward more elastomeric. For this purpose, polyethylene is modified either chemically, using peroxide or silane, or physically by radiation. In the present work, a cross-linkable polyethylene grade that can be processed by rotational molding was peroxide cross-linked under variation of temperature and time. Subsequently, the material was characterized by differential scanning calorimetry, tensile tests, notched bar impact tests and permeation measurements. Two of the altogether six parameter combinations investigated did not lead to successful cross-linking resulting in very poor toughness. Stiffness, strength and permeation barrier properties, however, were much better than those of the other series due to higher crystallinity. Mechanical, physical and chemical properties changed significantly by successful cross-linking. The impact strength could be improved by a factor of more than 10. At the same time, significant losses in stiffness, strength and permeation barrier properties had to be accepted. Peroxide induced randomly distributed formation of cross-links above the melting point interfered with formation of crystalline regions upon cooling.

Bolted joints are one of the most used joining technologies in engineering. It is possible to join different kind of materials and to transmit heavy loads. Nevertheless, they are vulnerable to fatigue cracks. The present research investigates the dependency between the preload of the bolt and the initiation of a fatigue crack in the bolted sheet. Therefore, a representative bolt connection with a bolt of size M22 was selected in combination with a 5 mm thick sheet made of steel S355MC (1.0976). The bolted sheet was loaded by a fluctuating tension load and a load ratio of 0.1. The test results show a strong correlation of the preload and the number of load cycles to crack for preloads from 0 kN to 30 kN. The load cycles to crack are increased by about factor 20 by using a preload in contrast to the sheet without any preload. For higher preloads, the load cycles to crack does not change considerably. However, the crack initiation location changes by increasing the preload. For small preloads, the crack starts at the bolt hole, and for high preloads, the crack starts at the fretting zone.

For its good mechanical, thermal, and chemical property, ceramic materials are widely used in construction, chemical industry, electric power, communication and other fields. However, due to its particularity and complex production process, quality problems usually occur, of which the most common one is surface defects. For ceramic products, the defects are usually small and complicated, and manual methods are difficult to ensure the accuracy and speed of detection. Relevant researchers have proposed a variety of machine vision-based ceramic defect detection methods, but these methods still need to break through in solving the key problems of ceramic surface glaze reflection, complex detection environment, low algorithm efficiency and low real-time performance. To this end, this article reviews the application status of machine vision on ceramic surface defect detection in recent years, summarizes and analyzes the existing non-destructive testing (NDT) technology method, and points out the main factors that affect the development of ceramic surfaces defect detection technology and puts forward the corresponding solutions.

During the welding process of welded joints in nuclear power plants, uneven deformation caused by temperature changes will lead to the generation of residual stress. Aiming at the problem that the demarcate experiment is easy to cause errors when the traditional indentation strain method is used to measure the residual stress. Using 316L austenitic stainless steel as an example, ABAQUS finite element simulation is combined with physical experiments to study the effects of different indentation depths on the strain increment after unloading under a state of residual stress. The results show that the indentation depth and strain increment are linearly related. Based on the linear relationship, an independent parameter that characterizes the residual stress is obtained and a model between the parameter and residual stress established. It provides a certain basis for the convenience and precise detection of residual stress in nuclear power plants machinery structures in service.

In this article, a gas tungsten arc welding is used as a high energy density beam to form a surface over 0.15% carbon steel with FeB, FeMo, and graphite powders. The microstructure, microhardness, and dry-sliding wear behavior of the composite coating were investigated using optical micrography, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectrometry. Microstructural investigations reveal that FeB-reinforced coating exhibited a homogeneous microstructure that consists of dendrites and eutectic. A lot of types of carbide and borides were formed. MoB 4 , Fe 2 MoC, B 8 C, Mo 2 BC, MoB, Fe 3 Mo, Fe 3 B, B 25 C, Fe 7 C 3 , FeB, Mo 2 B 5 , and MoC were seen in coated surfaces. Graphite iron boride coatings obtained by the gas tungsten arc welding process improved the wear resistance of carbon steel.

This paper is about the structural design optimization of the torsional arc spring and the dual-mass flywheel (DMF) using three different population-based optimization techniques: Particle swarm optimization (PSO), differential evolution (DE), and genetic algorithm (GA). For this purpose, the equations of the motions of the vehicle powertrain are derived and implemented into the dynamic analysis to minimize the vehicle torsional vibrations. The parameters and initial angles of the arc spring are optimized by considering the objective function that is the sum of the maximum acceleration amplitudes of the crankshaft vibrations. The results demonstrated that the proposed design procedure is able to provide a proper arc spring and DMF inertias to reduce the torsional vibration significantly. Moreover, it is indicated that the DE optimization techniques provide best performances than others. Finally, it is also shown that the natural frequencies can be reduced by the DMF and the optimization results are under the idling critical speed of the engine. The obtained results of this paper are of utmost importance for the arc spring manufacturer about the design process considering both DMF and spring parameters simultaneously to minimize torsional vibration of the vehicle powertrain.

In this study, AISI 316L stainless steel alloy samples were borided with powder-pack boriding method using Ekabor II powder with the support of a microwave furnace with a power of 2.9 KW and a frequency of 2.45 GHz. Boriding was carried out at 850, 900 and 950 °C temperatures for 2, 4 and 6 h of operation. A distinct diffusion barrier consisting of Fe–Ni–Si elements was detected in borided samples at 950 °C for 4 and 6 h. As a result of the Daimler Benz Rockwell-C adhesion tests, regions with insufficient adhesion strength were detected in these samples. In other samples, adhesion qualities between boride layers and substrate were in the range of HF1–HF3. The lowest specific wear rates were determined as 5.208 (mm 3  Nm −1 ) × 10 −6 and 5.210 (mm 3  Nm −1 ) × 10 −6 for the samples borided for 6 h at 850 °C and 4 h at 900 °C, respectively. It was determined that the increase in thickness of the brittle FeB compound increased the wear with the three-body abrasive wear mechanism.

Wire arc additive manufacturing (WAAM) offers high-quality technology for producing large complex geometry structures in close proximity to near-net form, using cost-effective manufacturing resources, such as welding and wiring materials. In this study, the cold-metal-transfer-based WAAM system was utilized to manufacture the steel cylindrical component. The mechanical properties and microstructure analysis of the component were analyzed at two regions (bottom and top region) along the building direction. The results showed that the microstructure of the part differed from the bottom to the top region, resulting in a hardness difference between 169 and 181 (Hv 0.5 ), and impact toughness varied from 72 to 80 J. There were also anisotropic features in the tensile properties: the yield strength and the ultimate tensile strength ranging from 401 to 457 MPa and between 492 and 543 MPa, respectively.

Understanding the relationship between core/face adhesive interface and performance of MWCNT added nanoadhesives are essential for better designing and fabrication of aluminum honeycomb sandwich panels. In this study, we used multi-walled carbon nanotubes (MWCNTs) to prepare enhanced interfacial adhesion between honeycomb core and aluminum facesheet. MWCNTs are first introduced to isocyanate, and then MWCNTs/isocyanate blend poured into polyol to produce MWCNTs reinforced polyurethane (PU) nanoadhesives. The relationship between core/face adhesive interface and performance of MWCNT added nanoadhesives are investigated in detail in terms of thermogravimetric analyses (TGA), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, edge-wise compression tests, flat-wise tensile tests and three-point bending tests The experimental results showed that the MWCNT addition to PU adhesive led to enhanced thermal stability, flat-wise tensile strength and edge-wise compression strength for sandwich structures. This study gives a significant reference indicator on the fabrication of an improved core/face interface for obtaining sandwich panels with desired mechanical properties.

In this study, mechanical responses of a friction welded AA6013/AA7075 aluminum alloy beam are investigated. For this purpose, the experimental study is conducted with two different friction welding parameters (i.e., rotational speed and welding pressure) and two constant friction welding parameters (i.e., friction pressure and contact time). Microstructural and mechanical performance analyses (i.e., macrohardness and tensile measurements) are considered to determine the weld quality. Effects of speed and welding pressure on the vibration characteristics/structural performances are also examined experimentally. Advantages of using vibration analysis are discussed to understand the effects of different weld parameters. Results are given in tabular and graphical forms.

The purpose of this research article is to show the effect of carbon nanotubes (CNTs) addition on fiber reinforced polymer matrix composites produced by the vacuum infusion method on tensile performance. In this study, glass, carbon, and fiber fabric reinforced polymer matrix composite plates were produced using glass, carbon and aramid fiber fabrics with the same weave type and similar areal density. Using the same production parameters, the composite plates reinforced with different fiber types were produced with CNTs addition by 0.5 wt% of total composite. Additionally, since it is thought that the effect of CNTs on performance in different fiber types may be different, hybrid fiber fabric reinforced composite plate material containing a composition of glass, carbon and fiber fabrics was produced and this material was produced with CNTs additive using the same production parameters as in previous fiber reinforced composite plate productions. In the study, composite plates with and without CNTs were produced in various compositions including glass, carbon, aramid, and hybrid fiber fabrics. As a result, CNTs reinforcement has increased the mechanical performance under tensile stress in glass, carbon, and hybrid reinforced fabric composite structures, but on aramid fiber, CNTs has decreased the performance.