Band 64, Heft 9

The multi-pass fillet welds of casing pipe were welded onto the in-service pipeline, which is widely used in pipeline repairs. However, the residual stress of repairing welded joints is larger, and it is easy to cause cracks in the heat-affected zone. In this paper, the local heat treatment was used to adjust the residual stress of the repaired welded joint of the in-service pipeline. The results show that the local heat treatment is very useful for reducing the residual stress of the repair welding joint of the in-service pipeline.

Among copper alloys, the precipitation (age) hardening quadruple CuCoNiBe alloys due to their superior mechanical properties in terms of the highest strength and elasticity achieved by peak aging have been used over the years in a wide range of industrial applications including aircrafts, coil systems, blast-proof materials, and molding dies. Combined thermomechanical treatment (i.e., equal channel angular pressing [ECAP] processing followed by post-ECAP aging) can result in a further enhancement of the strength of CuCoNiBe alloys due to the grain refinement and the formation of fine precipitates from α-Cu supersaturated solid solution. In this study, for the first time, the effect of severe plastic deformation by ECAP processing on the mechanical behavior of CuCoNiBe alloys is discussed thoroughly based on the material responses to tensile and compressive loading conditions. The results show that, besides a considerable strength enhancement, ECAP processing leads to a strong tension-compression asymmetry and significantly accelerated precipitation kinetics in CuCoNiBe alloys.

For this study, Ni thin films were deposited on a glass substrate by using 200, 300, and 400 W direct-current magnetron sputtering method for observing the effect of sputtering power on the structural properties of thin films. Grain size, crystallinity, orientation, and texture of the deposited thin films were observed and evaluated by X-ray diffraction (XRD) analysis. According to XRD analysis, all thin films presented crystalline atomic structure. Furthermore, the effect of texture on the structural properties were observed using strain analysis and grain sizes that were calculated by Scherrer’s method and Williamson-Hall analysis. The analysis revealed that the grain size of sputter-deposited thin films increased linearly with respect to the increasing sputtering power. Additionally, the elastic modulus and indentation hardness of the samples were measured by nanoindentation method, and the results were evaluated in terms of grain size and texture. The highest grain size, 7.30 nm, was observed on a 400 W sputter-deposited sample, which also had the highest elastic modulus and indentation hardness values as 98 and 3.6 GPa, respectively.

In this study, the effect of the notch locations on the Charpy-V toughness values of the all-welded joint obtained using robotic flux-cored arc welding was investigated with respect to microstructures at the notch locations. Charpy impact tests were performed through the thickness with notch location at the centerline as well as off-set regions of the weld metal in addition to the microhardness measurements conducted. The detailed weld metal characterization was conducted using a stereo microscope, optical microscope, and scanning electron microscope at the same location where the Charpy tests and microhardness tests were performed. The sub-zero impact toughness test results indicated that the columnar weld metal regions exhibited low toughness values while the centerline microstructure consisting of mainly reheated regions displayed much higher toughness values even at the test temperature of −60 °C, satisfying the toughness requirement of the requested 47 J value. It is concluded that a small variation of the through-thickness notch position may result in different toughness values for the same weld metal. On this basis, the notching procedure of the Charpy-V samples for the multi-pass weld metal should be conducted with care and obtained results should be explained with respective notch position and microstructure.

In this study, the size effect of zircon (ZrSiO 4 ) on the tribological characteristics of polymer matrix friction composites were investigated. Hence, four friction composites containing micro and nano-sized zircon particles (5 and 10 wt%) were developed and produced using powder metallurgy method. Their wear and friction characteristics were examined using a friction-wear test device. The weight loss and specific wear rate were measured and compared with that obtained for microsized zircon particles. The surfaces of samples were analyzed using a scanning electron microscope, and less wear was observed in the samples containing nano-sized zircon particles. The results revealed that the size of abrasive particles plays a key role in enhancing the friction coefficient and friction stability.

In highly loaded components, such as roller bearings, early failures may occur due to microstructural defects. Thus, a higher defect tolerance of the material can improve the fatigue lifetime. To produce steels with high defect tolerance, innovative alloying concepts, and a sound knowledge of the influence of heat treatment parameters on the resultant mechanical properties is indispensable. Consequently, two bearing steels based on 100Cr6 with different silicon contents were investigated to achieve relatively high retained austenite (RA) fractions, which are assumed to increase the defect tolerance at cyclic loading. To understand the relation between bainitic heat treatment and mechanical characteristics, the resultant RA fractions, Vickers hardness, microhardness, and cyclic hardening exponent CHT e II , which correlates to defect tolerance of metallic materials, were determined for differently heat-treated conditions. Based on the statistical design of experiments and measurements obtained with X-ray diffraction and cyclic indentation testing, regression calculations were conducted. Pertaining to the results of the regression analyses, the heat treatment parameterizations of these steels were specifically determined for certain desired property combinations within the boundaries investigated. Therefore, the temperatures used in the austenitizing and bainitizing procedures have shown the highest influence on the mechanical characteristics and the RA fraction of both steels.

Astronomical devices, such as optical benches, carry high precision instrumentation work at low temperatures (−150 °C). To fulfill engineering requirements, glass-epoxy composite trusses are proposed. To evaluate the performance of this solution, thermomechanical characterization is carried out by means of dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), flammability tests, and tensile test and Scanning Electron Microscopy (SEM) observations. Two family of coupons are tested; first one environmentally aged for 10 years and second one recently fabricated, both at 20, 0 and −20 °C. Ageing influence is more noticeable on thermal behavior as Tg and self-extinguish capacity are lower. Ultimate tensile strength and maximum strain are lower for the aged coupons (16–25%), but there is not a remarkable difference in terms of stiffness. Also, coupons mechanically tested at −20 °C show a slight increment in strength. These results show that ageing of glass-epoxy composites must be considered when high performance devices are conceived to be fabricated with.

Adaptability of the metaheuristic (MH) algorithms in multidisciplinary platforms confirms its significance and effectiveness for the solution of the constraints problems. In this article, one of the imperative thermal system components-plate fin heat exchangers is economically optimized using the novel artificial gorilla troops optimization algorithms (AGTOAs). The cost optimization challenge of the PFHE includes the initial and running cost that needs to be minimized by optimizing several design variables subjecting to critical boundary conditions. To confirm the performance of the AGTOA, the statistical results obtained were compared with nine benchmark MHs algorithms. It was found that AGTO is a robust optimization algorithm because it was able to fetch the best results for the function with 100% of the success rate compared to the rest of the algorithms. Moreover, considering the superior results obtained from the AGTO, it can be applied to numerous applications of the engineering design optimization.

In the present study, cementation steel was exposed to boronizing process at 950 °C for 6, 8, and 10 h. Microstructural changes on the surface of the samples after boron operation were inspected by optical microscope, scanning electron microscope, energy-dispersive spectroscopy, X-ray diffraction, electron back-scatter diffraction, and elemental mapping analysis. In addition, surface roughness, microhardness, and boride layer thicknesses were measured. The boride layers deposited on the cementation steel consisted either single or double phases. The level of boride deposit of all samples was achieved from 90 to 156 μm. The boride layer created at 950 °C for 10 h involved the FeB and Fe 2 B. The boride layers had a much higher hardness value than the substrate material due to the presence of FeB and Fe 2 B.

Numerical study was carried out for layered composite plates joined with both interspaced and interspaced double-lap joint subject to tensile load. The numerical analyses were actualized using ANSYS 14.5 software package based on finite elements method. The layered composite plates with different orientation angles were considered. It was considered that the composite plates and patches were carbon/epoxy (AS4/3501-6) and the composite plates were joined using DP 410 adhesive. The studies started with the determination of the failure loads the stresses in these loads were obtained. Normal and shear stress in all directions were obtained via numerical analyses for composite layers and adhesive layers throughout radial thickness. Moreover, the von–Mises stress distributions that develop on the adhesive were obtained as well. The effects of adhesive and orientation angles were examined at the adhesive and composite layers interfaces. The effect of the surfaces is great in the gap-free bonding of the surfaces. But the strength of the adhesive is more important than the condition of the adhesion surfaces in interspaced bonding.

One of the most important variables that determine the braking performance of heavy-duty trucks is the high temperature increases in the brake components. In this study, the effects of high temperatures in brake lining compositions were investigated using thermogravimetric analysis (TGA). Furthermore, dynamometer tests and SEM analysis were performed. Three different compositions, which are called standard, fly ash and sisal fiber mixture, were compared with existing commercial heavy-duty truck brake lining. The thermal behavior of samples analyzed in TGA machine compared to the weight losses with increasing temperatures until 900 °C. Dynamometer tests which simulated the real part production and vehicle tests were realized in brake lining supplier. Finally, with the SEM analysis, both normal and worn surfaces were analyzed and reasons for wear surfaces were investigated. The findings suggest that there is a high potential in fly ash mixture to apply in commercial trucks applications which occurs at very high temperatures and is very suitable for environment and cost reduction points.

Some machines, such as heavy presses and rammers, can be exposed to big shock and inertial forces under dynamic severe working conditions. Even if vibration isolation to the foundations of machines operating under dynamic loads is applied, the exposure of these machines to shock and resonance loads may not be adequately prevented. The sensitivity of these machines, the product quality, or life span can also incredibly decrease. Therefore, it is essential to know the vibration behaviors of machine bodies and parts. This study investigates vibration characteristics of polymer matrix composite (PMC) materials by the experimental modal test method. Nine different composite beam samples having sizes of 20 × 25 × 480 mm were produced for modal tests. Composite beams contain different ratios of aggregate and epoxy resin. Each composite beam’s natural frequencies and damping ratios were defined with frequency response and coherence functions taken from the experimental modal tests. The results from the modal analysis revealed that the most influential parameter on the vibration properties was the gravel ratio. As a result of the experimental study, it was concluded that while epoxy-resin, gravel and fine-sand additives increased the stiffness of PMC beam, gravel and fine sand additives also increased the damping rate of PMC beam.

With the rapid development in the technological, industrial, and defense industries, the joining of metallic materials used becomes very important. Various problems may arise in metallic materials joined by traditional fusion welding methods. The friction welding technique, which is one of the solid-state welding types that contains minimum welding defects and creates minimum internal stresses after welding, can be used in order to reduce the negativities in different steel joining. Thus, the negativities in fusion welding methods are reduced. The friction welding is a plastic deformation and extrusion process that uses heat to convert mechanical energy generated by friction between the interfaces of these two material pairs as a result of one material rotating at a stationary speed and the other rotating at a rotary speed into thermal energy. The heating phase (friction phase) is the time until the end of the welding process. During this time, the surfaces are under pressure. The formation of temperature in steel is between 900 and 1300 °C, and this temperature is reached in a very short time. Thus, parts are joined together by the pressing force. Materials that are very difficult to join with fusion welding can be joined more easily by friction welding.