Volume 67, Issue 4

This study investigates the bending performance of wavy spider web honeycomb sandwich structures produced using polylactic acid (PLA) through 3D printing technology. The primary objective is to enhance mechanical efficiency per unit mass by integrating wave and spider web profiles, a novel approach in the literature. Tensile specimens and sandwich structures were manufactured according to ASTM standards, and their mechanical properties, including stress-strain curves, modulus of elasticity, and Poisson’s ratio, were determined through tensile tests. Bending tests on straight, wavy, and spider web designs were conducted to obtain force-deformation curves and post-testing damage images. Finite element models in Ls-Dyna, validated by experimental data, showed that the wavy model achieved the highest specific energy absorption (sEA) while the spider web model exhibited the highest specific peak crushing force (sPCF). The wavy spider web model demonstrated the second-highest values for both metrics, supporting the development of next-generation sandwich structures where specific strength and energy absorption are critical.

High-speed rail wheels are critical components responsible for load-carrying, guiding, and transferring traction and braking forces, impacting the safety, stability, and reliability of trains. Among the mechanical properties of high-speed rail wheels, tensile properties influence both heat treatment and overall performance evaluation. This study investigated the tensile properties of the rim and spoke of high-speed rail wheels using both conventional and tiny specimens. Additionally, tensile tests were conducted on tiny specimens sampled along the axial and circumferential directions of the wheel rim to assess the distribution of tensile properties. The tensile properties of tiny specimens of the spoke closely aligned with those of conventional specimens. However, the results obtained using tiny and conventional specimens of the wheel rim, although similar, showed greater variability. The tensile properties of the wheel rim exhibited a gradient distribution, with the highest tensile strength near the tread side and the lowest near the spoke side. The plasticity parameters showed minimal variation along both the axial and circumferential directions of the rim. This study provides valuable insights for optimizing the production process of high-speed rail wheels, ultimately enhancing their overall quality. The findings are significant for improving technical support in the manufacturing of high-speed rail wheels.

Construction steels must have many mechanical properties according to standards. One of these is suitable impact resistance feature. In the research, the impact transition temperatures of the construction steels produced from scrap in Türkiye as B500B-00, B500C-00, GR60T-01, GR60T-BR, GR60T-02 standards were determined in the range of +60/−30 °C temperatures. The microstructures of the samples were observed by scanning electron microscopy, X-ray diffraction. Tensile and microhardness tests were performed on the samples. Fracture surfaces of samples were examined by using SEM. The Charpy fracture energies of five different quality construction steels were detected between 76 and 105 J at 60 °C and 14–22 J at −30 °C. Izod fracture energies were measured between 100 and 135 J at 60 °C and between 35 and 48 J at −30 °C. The impact transition temperatures of the samples were determined in the range of 35 °C to −5 °C.

This study investigates the behavior of an in-house cast directionally solidified nickel-based superalloy (i.e. CM247LC grade alloy) at low and high temperatures (760 and 982 °C, respectively). For this purpose, creep and tensile tests were conducted on the alloy after the heat treatment consisted of solutionizing and double aging. Following creep and tensile tests, microstructural examinations were made on the fracture surface and cross-sections of samples by using optical, digital, and electron microscopes. The results showed that the dominant creep mechanism of the CM247LC alloy was dislocation creep at both temperatures. However, the higher temperature accelerated creep failure via de-binding at the matrix/carbide interface and caused severe structural degradation.

Corrosion significantly impacts the welding of dissimilar components, leading to a decrease in the lifespan of products. The primary aim of this research is to examine the corrosion behavior of the weld region in dissimilar welding of Inconel 625 and AISI 316L plates with a thickness of 20 mm. The plates are weld together by using continuous current gas tungsten arc welding (CCGTA) and pulsed current gas tungsten arc welding (PCGTAW) methods. The process employs ERNiCr-3, TIG 316L, and a twisted combination of both filler metals (ERNiCr-3+TIG 316L). Specimens with dimensions of 12 mm × 20 mm × 42 mm are obtained by cutting the weld samples for corrosion tests. The divided parts are each submerged in a 100 ml pool of sulfuric acid and are maintained for a combined duration of 240 h. A weight loss investigation is undertaken, in addition to metallurgical characterizations of the specimens. Energy Dispersive Spectroscopy (EDS) in conjunction with Scanning Electron Microscopy (SEM) are utilized to conduct metallurgical investigations. It is observed that twisted filler metal and CCGTA welding method results in the highest amount of mass loss. The least corroded sample is obtained by using twisted filler metal combined with PCGTA welding method.

The efficacy of hot-dip galvanizing coatings in safeguarding steel components against corrosion largely hinges on the formation of a stable layer of corrosion products atop the coating. However, precise quantification of the resistance of this natural passive layer and the impact of climatic factors on its formation kinetics remain insufficiently understood. In a series of tests, the initial formation of the passive layer on zinc coatings conforming to DIN EN ISO 1461 under atmospheric weathering conditions using an electrochemical test method with gel electrolytes was examined. To this end, test specimens underwent galvanization in two different variants and were subjected to outdoor weathering for four weeks during both summer and winter. Electrochemical measurements conducted during this period yielded consistent and reproducible results for zinc coatings featuring an external pure zinc phase. The polarization resistance exhibited gradual development in several stages contingent upon the prevailing climatic conditions. Additionally, microscopic and macroscopic analyses indicated that the crystalline structure of galvanizing coatings, characterized by distinct zinc spangles, influenced the local properties of the surface layer. Conversely, samples with zinc coatings featuring continuous zinc-iron phases did not yield interpretable results using the gel-based measurement approach.

In this research, nodular cast iron (GGG50) with 0.2 wt.% Cr and 0.8 wt.% Mo was subjected to austenization at 900, and 950 °C for 45 min, and 1 h. Then, austempering was performed at 200, 250, 300, 350 and 400 °C for periods of 30–720 min. The microstructure of the austempered samples at varying temperatures was defined using an optical and scanning electron microscope. Phases and compounds were analyzed through X-ray diffraction. Hardness tests were conducted on the samples. Wear performances were assessed using a pin-on-disc wear apparatus. The friction coefficients of the materials were detected. The worn surfaces of the samples were examined by scanning electron microscope (SEM). The microstructure of the casting was comprised of ferrite and pearlite. In contrast, the annealed sample contained a blend of acicular ferrite and carbon-enriched annealed iron, referred to as “ausferrite.” As the austempering temperature increased, the structure became coarser and the hardness values declined. As the annealing temperature increased, wear resistance was observed to decrease. The coefficient of friction diminished as the austempering temperature raised.

Metaheuristics have evolved as a strong family of optimization algorithms capable of handling complicated real-world problems that are frequently non-linear, non-convex, and multidimensional in character. These algorithms efficiently explore and take advantage of search areas by imitating natural processes. In addition to introducing a unique modified hippopotamus optimization algorithm (MHOA) in conjunction with artificial neural networks (ANN), this research examines the most recent developments in metaheuristics. By utilizing ANN’s adaptive learning processes, MHOA improves on the original hippopotamus optimization algorithm (HOA) in terms of convergence and solution quality. The study uses MHOA to solve a number of engineering design optimization issues, such as gearbox weight reduction, robot gripper design, structural optimization, and piston lever design. When compared to more conventional algorithms, MHOA performs better in terms of accuracy, robustness, and convergence time.

Hole-drilling method is a standardized technique for obtaining residual stresses in isotropic structures. Previous studies provide a foundation that enables the use of this method to investigate orthotropic structures, such as fiber-reinforced composites. In this study, the incremental hole-drilling method was applied to investigate residual stresses in filament wound type 4 composite pressure vessels. The investigated composite cylinders were manufactured with different internal pressure functions during the winding process, to achieve distinct residual stress states. Additionally, the influence of the initial loading under sustained internal pressure and increased temperature on the stress distribution was investigated. It was shown that the residual stress state can be influenced by varying the internal pressure in the winding process. After testing at sustained load and increased temperature, a stress redistribution was observed, which took place due to creep phenomena. Finally, a discussion of the challenges for the application of the hole-drilling method to composite pressure vessels is provided.

Armor steels are crucial for their high hardness and toughness, providing protection in military and security applications, including vehicles and personal body armor. This study aims to assess the fatigue strength of welded armor steels having different weld penetration. Weld fusion or penetration (FOP) is an important issue in terms of welded joint strength. Especially in non-load carrying joints, how the fatigue strength will change with the increase in weld FOP can only be determined by the tests to be performed. In this context, the joint type was chosen as a non-load carrying cruciform joint in this study. Weld FOP is determined in terms of length in many studies. In this study, these values were evaluated in terms of unit of area as well as length. In addition to the experimental fatigue studies, specimens having different weld FOP rates were modeled and hot-spot stress analyses were performed by ANSYS workbench. As a result of the studies, a decrease in fatigue strength was determined by the increase in the weld FOP rate. The analysis revealed that as FOP rate increased, the hot-spot stress values became closer to the nominal stress.

In this study, the effects of the hole-distance from impact point and numbers of holes on carbon-glass/epoxy composite plates formed by three different intraply hybridizations subjected to repeated (multiple) impact loading with 8 J energy level are examined experimentally. The samples were subjected to multiple impact loading until perforation, which is determined by the impactor moving completely through the samples. The number of repeats for each sample was determined by the impactor perforating the sample. In order to better interpret the effect of the test parameters after of the impact tests, contact force-time and contact force-deflection, contact force-number of repeats and number of repeats-hybridization type change graphs of the samples are given for each hybridization type. Thus, the effects of both hybridization type and number and distance of holes on the repeated impact resistance of carbon-glass/epoxy intraply hybrid composite plates were investigated. Considering all test parameters, the absence of a hole and the hole’s near to the center of the sample significantly affects the sample stiffness, resulting in lower impact resistance. The presence of the hole and its distance from the impact point made the sample more resistant to impact. While the highest number of repeats was obtained for samples no-hole (d0h0), the lowest number of repeats was obtained for samples with four holes at a distance of 10 mm and 20 mm from the impact point. For all three hybridization types, the contact force value gradually decreased as the number of impact repeats of the samples increased. When the change in the damage areas of the samples was examined, the largest damage area occurred in the samples without holes (d0h0). Damage progression generally occurred in the 0° orientation of the lower layer.

It is essential to obtain preliminary design data of composite marine vehicles operated in harsh marine environments, such as those with hygrothermal and impact effects. The effects of hygrothermal aging and stacking sequence on the low-velocity impact (LVI) response of carbon fiber epoxy composite plates (CFRP) were investigated experimentally. CFRP plates in six orientations [0°/90°/45°/−45°]s, [90°/45°/−45°/0°]s, [0°/90°/0°/90°]s, [90°/0°/90°/0°]s, [−45°/45°/−45°/45°]s, and [45°/−45°/45°/−45°]s (quasi-isotropic, cross-ply, and angle-ply) were manufactured using a vacuum-assisted resin infusion method. LVI tests were performed by using the Ceast 9350 Fractovis Plus impact machine. Four aging conditions (atmospheric, 2, 4, and 6 weeks aged) were simulated using Ascott CC 1000ip programmable salt spray and cyclic corrosion test chamber cabin. The effect of the ply-stacking sequence plays an important role in the failure of the top or bottom surface of the plate samples and dent depth. When 0-degree fiber is used on the upper and lower surfaces of the plates, the dent depth is lowest, followed by 90, +45, and −45°, respectively. Dent depth and top surface fiber cracking lengths generally decrease as the process begins with initial atmospheric conditions reaching 6 weeks.

In this study, a recent approach was developed to simulate the boronizing kinetics and subsequent phase homogenization (B + PH) in AISI 1045 steel. The Taylor expansion model was employed, taking into account the boron concentration profile in each layer (FeB or Fe 2 B) as a second-order Taylor series under a transient diffusion regime. Two dimensionless constants were integrated into the model to infer the boron diffusion coefficients in FeB and Fe 2 B, and to calculate the corresponding boron activation energies. The differential equations were then adapted to simulate the phase homogenization (PH) kinetics that follows the boriding process in AISI 1045 steel. Simple relationships were derived to predict the necessary dissolution time to achieve a maximum thickness of the Fe 2 B layer. Additionally, the mass gain per unit area associated with Fe 2 B layer formation, along with its evolution during phase homogenization, was modelled based on the chosen process variables.

This study experimentally investigated the parameters such as dynamic hardening, inertia track cross-sectional area, decoupler hardness, and fluid volume affecting the damping properties of passive hydraulic engine mounts. Two levels were determined for these parameters, and the full factorial design of experiment (DoE) was created. According to the DoE, hydraulic engine mounts with various design configurations were assembled and tested. Based on the test results, a response surface was created in the Hyperstudy software, and the optimal parameters were obtained via the surface for the desired hydraulic mount performance. Another mount close to the optimum design configuration was then analyzed by the Hyperstudy, and the analysis results were confirmed with the test results. It was observed that the experimental and analysis results were consistent. As a result, it has been demonstrated that the mount parameters can be decided with the response surface generated with the DoE. So, both time and cost advantages can be achieved by eliminating trial and error in production.

The current study aims to utilize a unique hybrid optimizer called oppositional-based learning and laplacian crossover augmented material generation algorithm (MGA-OBL-LP) to solve engineering design problems. The oppositional-based learning and laplacian crossover approaches are used to address the local optima trap weakness of a recently discovered MGA algorithm that has been added to the fundamental MGA structure. The proposed hybridization strategy aimed to make it easier to improve the exploration-exploitation behavior of the MGA algorithm. The performance of the proposed hybridized algorithm was compared with other notable metaheuristics collected from the literature for four constrained engineering design problems in order to determine whether it would be practical in real-world applications. A comparison analysis is undertaken to confirm the MGA-OBL-LP algorithm’s competence in terms of solution quality and stability, and it is discovered to be robust in addressing difficult practical problems.