Band 65, Heft 8

Failure caused by stress corrosion cracking (SCC) is inevitable during the long-term service of nuclear power pipe welds. This is mainly due to the propagation of microcracks in the deposited metal, which seriously affects the operation safety of nuclear power pressure pipes. Overlay welding is practical for pressure pipe repair welding, which can introduce compressive residual stress inside the weld seam. In this work, a diagonal T-pipe joint was fabricated using tungsten inert gas arc welding with ERRS-3 wire, and an overlay weld was also fabricated using tungsten inert gas arc welding with ERRS-3 wire under circumstances of water in the pipe and no water in the pipe. And then the contour method and finite element method were employed to measure and calculate the residual stress distribution in the diagonal T-pipe joint. Both results showed that overlay welding can introduce compressive residual stresses into the pipe joint. The compressive residual stress zone area inside the weld seam with water in the pipe is larger than that without water in the pipe, and the compressive residual stress zone area varies at different positions of the weld seam. This work is expected to promote the application of overlay weld technology in the diagonal T-shaped pipe joint repair and prevent stress corrosion crack propagation of nuclear power pipe welds.

Currently used methods for processing allogeneic bone grafts like gamma irradiation are connected with downside of altering the mechanical properties of the graft. As an alternative, high hydrostatic pressure (HHP) leads to an effective devitalization of cells without influencing the bone matrix and its mechanical behavior. To address the clinical application, bone plates were prepared out of HHP-treated bone granules, which are conceivable for augmentations in the jaw region. In order to achieve sufficient mechanical strength, two different adhesives were tested. Mechanical characterization by three-point bending tests was performed. Furthermore, analysis regarding cytotoxicity as well as colonization experiments with mesenchymal stem cells were performed to investigate osteoconductive properties of the bone plates. While plates composed of fibrin glue showed better biocompatibility, plates prepared with Loctite ® 408 showed better mechanical properties and could be incorporated in a model application. Regardless of the adhesive, bone plates induced osteogenic differentiation compared to cells cultured without bone plates. Although an adhesive combining both properties would be necessary for later clinical application, the study at hand demonstrates the possibility of producing allogeneic bone plates from HHP-treated granules, which meet the basic requirements for jaw augmentation.

Descaling of stainless-steel black coil is an important step to produce white coil with smooth glossy surface. The AISI 304L black and white coils from a company containing 1.08–1.71Mn and 0.22–0.40Cu (wt%) were used to study the effects of Mn and Cu on descaling rate by potentiodynamic polarization technique at 25 °C. The pickling solutions were 0.5 M HCl and 0.5 M HCl mixed with H 2 O 2 of 0.5, 0.88 and 1.76 M. The polarization curves of black and white coil samples measured in HCl–H 2 O 2 mixture showed no passive range. The descaling rate of black coil oxide scales, and the corrosion potential ( E corr ) increased with H 2 O 2 concentration. Low-Mn sample, that is 1.08%Mn0.23%Cu sample, showed higher descaling rate than high-Mn samples. No effects of Cu content on the descaling rate were observed. For white coil samples, the descaling rates were almost constant, but pitting on surface was observed. Passive films were eliminated. The corrosion potentials of black and white coil samples increased when adding H 2 O 2 in HCl solution indicating an increase in cathodic reaction due to increase in dissolved oxygen. The corrosion potentials of 1.08%Mn0.23%Cu black and white coil samples were lower than those of high-Mn samples corresponding to less Mn oxide.

This research work studied the effect of aluminium, cobalt and nickel additions in superalloys grade GTD-111 and IN-738 on morphology of gamma prime particles and their lattice misfits after subjected to heat treatment and long-term cyclic exposure by using SEM and XRD. It was found that the particles became more cuboidal in shape after heat treatment in modified GTD-111 and IN-738 alloys. When adding 1 wt% aluminium and 6 wt% nickel, larger negative values of lattice misfit were found at −0.57 % and −0.28 %, respectively. However, 6 wt% cobalt addition reduced the negative value of the lattice misfit to −0.20 % in modified GTD-111 and small positive lattice misfit (+0.08 %) was found in modified IN-738. Also, modified GTD-111 alloy shows more spherical shape of the gamma prime precipitates than those in modified IN-738. After long-term cyclic exposure at 1173 K for 1440 ks, it was found that the particles become more spherical shape comparing to those of heat treated ones. The shape of particles in both modified alloys with 1 wt% aluminium and 6 wt% nickel additions maintained more cuboidal compared to others. Furthermore, the effect of 6 wt% cobalt addition is more pronounced for modified IN-738 than that of modified GTD-111.

In this paper, a high energy density beam of gas tungsten arc welding (GTAW) was employed to build a surface over low carbon steel with FeMn, FeB, and graphite powders. X-ray diffraction, optical microscopy, energy dispersive X-ray analysis, scanning electron microscopy, micro hardness tester, and adhesive wear tester were used for researching behavior of the composite coating which microstructure, hardness and dry-sliding wear. Many different carbides and borides, including Mn 5 C 2 , Fe 3 C, B 8 C, MnB, B 4 C, Fe 3 B, Fe 7 C 3 , FeB, and Mn 2 B, were found on the coated surfaces. The microstructure analysis shows that the shape of the graphite also depends on the FeMn–FeB–C content. The smallest weight loss was obtained from Sample S4 and the critical sliding distance was enhanced by adding graphite from 5 to 20 wt% at transition from oxidative to abrasive.

Electric motors in automotive applications are subjected to high thermal and structural loads, while having strict requirements regarding dimensions, mass, and costs. The design of such motors requires sophisticated simulation models. The laminate stack in the rotor of such a motor is made of steel sheets and behaves transversally isotropic: the radial stiffness is equivalent to steel, and in the axial direction, it has a highly progressive nonlinear stiffness characteristic. The loading and unloading stiffness curves change from cycle to cycle when subjected to repetitive loads. In this paper, the usage of a single approximating curve to describe the longitudinal stiffness of the laminate stack is proposed. This approximation can be used in FEM models to reproduce the structural nonlinear behavior of such a laminate stack using a simpler approach than implementing the full loading and unloading curves in a material model, at a price of negligible loss of precision.

In this study, thin-walled open channel angular pressing (TWO-CAP) technique was applied to pure copper specimens as a novel severe plastic deformation (SPD) method. The TWO-CAP process was applied to the specimens up to four passes. After each pass, the microstructural and mechanical characterization of the material was investigated by tensile and hardness tests along with OM, SEM, EDS, TEM and XRD analyses. As a result, a highly increase in the mechanical properties was obtained, in addition satisfactory grain refinement was observed in microstructures. Strength and hardness values were positively affected from the minimizing the grain sizes after TWO-CAP process. Another reason of the improvements in mechanical properties can be explained as the increase in dislocation density. Furthermore, the effect of the TWO-CAP process on the dislocation density of the material has been demonstrated by XRD and TEM analyses in nanoscale. Moreover, the strain equation has been developed analytically and the effect of each pass on strain was calculated. Finally, the effect of the process on the stress-strain properties of the material was examined by the numerical analysis method and the study was verified.

It has been interesting in industrial applications due to the advantages provided by laminated composite applications. Composite materials are of great importance in design optimization due to the advantages they provide, such as lightweight, high strength value, and design flexibility. Finite element programs and artificial intelligence optimization techniques developed in recent years are effectively used in the design of composite materials. In order to optimize the angular orientations of the composite disc, analyses are made using the finite element program. Particle swarm optimization algorithm (PSO), genetic algorithm (GA), and hunger games search optimization algorithm(HGS) are used to determine the best stacking angle value on the disc plate using the analysis data obtained after the completion of the analyses. When the results obtained were examined, it was determined that the results obtained from particle swarm optimization, genetic algorithm, and hunger games search optimization techniques showed that hunger games search optimization algorithm gives better results as other and HGS could be used for the stacking of composite materials.

Thermal system optimization is always a challenging task due to several constraints and critical concepts of thermo-hydraulic aspects. Heat exchangers are one of those devices that are widely adopted in thermal industries for various applications such as cryogenics, heat recovery, and heat transfer applications. According to the flow configurations and enhancement of fins, the heat exchangers are classified as plate-fin heat exchangers, shell and tube heat exchangers, and tube-fin heat exchangers. This article addresses the economic optimization challenge of plate-fin heat exchangers using cheetah optimization (CO) algorithm. The design variables were optimized using the CO algorithm, and statistical results were compared with eight well-established algorithms. The study revealed that the cheetah algorithm is prominent in terms of realizing minimizing the overall cost of the plate-fin heat exchanger with a 100 % of success rate. Furthermore, the study suggests adopting the cheetah optimizer for solving optimization challenges in different fields.

In this study, titanium and niobium element powders in determined amounts (0.25 and 0.5 wt%) were added into the 316L stainless steel matrix by means of powder metallurgy (PM) technology, either singly or in pairs, and the desired composition was obtained as a powder mixture. The powders used in the study were cold pressed tensile sample molds prepared in ASTM 8 M standards, unidirectionally cold pressed under 700 MPa compression pressure and formed into blocks. After pressing, the raw strength samples were sintered in an atmosphere-controlled tube furnace at 1325 °C for 2 h in an argon atmosphere. The microstructure and mechanical properties of the produced PM steels were characterized by optical microscope, SEM, EDS, and tensile test. The results showed that the stainless-steel samples with 0.25(Ti–Nb) added composition to 316L stainless steel had the highest yield strength and tensile strengths. However, with the addition of 0.5Ti, 0.5Nb, and 0.5(Ti–Nb) to 316L stainless steel, a decrease was observed in the mechanical properties. Moreover, the MQL machining is better on the machining output such as surface roughness and cutting temperature than dry machining in terms of a sustainable machining process.

The goal of the present study is to investigate the influence of impactor shape on the low-velocity impact behavior of the composite panels manufactured with different reinforcement materials at the same thicknesses, experimentally. Kevlar, carbon, S-2 glass woven fabric and epoxy matrix have been used to manufacture thermoset composites with the vacuum-assisted resin infusion molding method. The Fractovis plus test machine with a 12.7 mm diameter hemispherical and two different conical impactor noses was used to perform impact tests. The effects of impactor shapes on the low-velocity impact behavior have been compared for 20 J, 40 J, and 60 J energy levels. Although at the same impact energy level, S-2 glass fiber-reinforced epoxy specimens have a higher perforation threshold than carbon and Kevlar fiber-reinforced epoxy. Because to achieve the same thickness, the number of S-2 glass layers was greater than the number of carbon and Kevlar layers. Additionally, the form of the impactor greatly influenced the perforation threshold.

In this study, the cutting parameters were optimized according to the thrust force and operation time in the drilling of Al 2024 T351 alloy, which is preferred in the aerospace industry and therefore subjected to thousands of drilling processes with liquid cooling. Cutting speed (70, 90, and 110 m min −1 ) and feed rate (0.08, 0.1, and 0.12 mm tooth −1 ) were considered cutting parameters. Experiments were performed three tool types (HSS, HSSE-Co5, HSSE-Co5 TiAlN coated). Taksan TMC-700 V CNC vertical machining center with FANUC control panel was used for drilling, and ESIT AX3 load cell and NI cDAQ-9188, data acquisition system, were used for data collection. Signal noise was reduced by applying the exponential smoothing method to all force data obtained in the experiments. The maximum forces in the machining direction ( z -axis) were determined for each hole. The time was calculated during the computer aided manufacturing process. Response surface optimizations, variance analyses (ANOVA), and regression analyses were performed using these determined maximum thrust forces and measured time.

Most of the structures in vehicles used in the automotive, aviation, and marine industries are exposed to different loads. It is seen that these structures are more exposed to flexural stress. Structures can sustain dangerous damage over time under the effects of flexural loads. The resistance of curved glass fiber reinforced polymer composites to flexural force is very important. In this study, the diameters of curved composites of 760 mm, 380 mm, and 304 mm are studied. Also, fiber stacking sequences were determined as [0/0/−45/+45/90/90] S and [90/90/−45/+45/0/0] S and compared. All specimens were produced by vacuum infusion method. Three-point flexural tests were performed according to the ASTM D7264 standard at 1 mm∙min −1 punch speed. Among all composites, 760 mm diameter and Type 2 stacking were found to have the highest flexural strength. Hence, it was observed that the flexural strength decreased with the increase in curvature, and Type 2 fiber layer sequencing is more durable than Type 1 sequencing. This is because the 90° fiber direction in the substrate has a damping effect on the applied force.

Light weight design is believed one of the most effective ways to enhance performance, reduce fuel consumption and harmful gases for air and land vehicles. Hence, welding lightweight metals like magnesium alloys is very important. Friction stir spot welding joints of 2 mm thick AZ91 magnesium alloy sheets by overlapping two of them were performed utilizing two welding tools having conical and triangular pin at 800, 1200 and 1600 revolution per minute (rpm) tool rotational velocities for each tool to identify the pin shape and rotation speed impact on microstructure and mechanical features of the created joints. The stir zones of the joints contained smaller grains, therefore had higher hardness in comparison to AZ91 base metal, thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ). The lowest hardness values were found in HAZ of the welds. Hardness fell slightly with a rise in rotation speed for both tools because of more heat input. Strength of the joints manufactured applying the triangular pin tool was better because this pin mixed materials better, thus created joints with bigger welding area and greater hardness. The strongest weld was fabricated by applying triangular pin tool and 1600 rpm.