Volume 65, Issue 9

Based on observation of gas bubbles evolving from crevices on slow strain rate test pieces during anodic corrosion the effect of applied potentials in chloride aqueous solutions on amount and composition of the gas together with fracture strains from the slow strain rate test of a 17-4 PH steel was investigated. As a result, increasing applied potentials provide a reduction of fracture strains together with an initial increase in volume of released hydrogen gas. The fracture surfaces exhibit increasing brittle appearance, as found in hydrogen cracking failures. The results confirm that during local anodic corrosion, hydrogen is produced that provokes hydrogen induced cracking following anodic dissolution. Respective local pH measurements under varying applied electric potentials, show the acidification of the pit-electrolyte. Additional model calculations elucidate the stepwise local anodic corrosion and its acidification process together with the hydrogen supported cracking. The model shows that the relative amount of hydrogen cracking will depend on the provided material data as well as on solution properties such as pH, chloride level, temperature and oxygen content. As an all over result, together with the model calculations, the experimental evidence of hydrogen evolution during anodic local corrosion confirms the contribution of hydrogen cracking to anodic stress corrosion cracking.

In this study, AISI 430 and HARDOX 500 steels were joined by cold metal transfer (CMT) welding method. The properties and microstructural changes of the welding and HAZ regions were investigated by OM and SEM analyses. Microhardness, notch impact, and tensile tests were performed to determine the mechanical properties of the welded specimens. The ruptured surfaces of the test specimens after the impact test were examined using SEM. Coarse grains were formed in the HAZ regions but were limited to the low-temperature input of the cold metal transfer welding. The N3 specimen was broken from AISI 430 base metal and the elongation amount was 16.32 mm. Tensile strengths were from 380 to 493 MPa. The mechanical properties of AISI 430 and HARDOX 500 steels combined with CMT welding increased significantly and weldability was proven possible.

The main objective of this investigation is to study the mechanical properties and microstructural features of rotary friction welded (RFW) UNS S42000 martensitic stainless-steel joints. The welded joints were stress relieved at 316 °C for 1 h holding followed by air cooling. The joints welded using the friction pressure of 60 MPa, forging pressure of 64 MPa, friction time of 18 s and forging time of 4 s exhibited superior tensile properties. Microstructure showed carbide precipitates and strain induced and partial strain induced martensite in weld zone for heat treated condition and coarser martensite and retained austenite for non-heat treated condition. Fractography for tensile tested samples reveals predominantly ductile mode of fracture for heat treated samples than non-heat treated condition. The Microhardness showed a higher value of hardness for the weld zone due to strain induced martensite and lesser hardness at PDZ due to partial strain hardened martensite.

The decarburization layer can be detrimental and lead failures in press hardened steels. This work investigates the effect of decarburization layer on the fatigue crack origination and growth on press hardened parts of uncoated 22MnB5 steel. The decarburization layer was analyzed by light microscope, scanning electron microscope, and microhardness measurements. It was found that decarburization layer has two distinct zones indicating complete and partial decarburization. To understand the effect of decarburization on crack origination, high cycle fatigue tests were performed on samples from press hardened parts in decarburized and polished (nondecarburized) conditions. The results have shown that the fatigue performance of press hardened steels in polished condition outperforms the fatigue samples in decarburized condition. In fractographic investigations, it was seen that decarburization is not only responsible for crack origination but also affects crack propagation by having full and partial decarburization zones. The full decarburization zone was acted as surface crack origination source. In the partial decarburization zone, the crack propagation behavior was changed by a complex phase microstructure of bainite, ferrite, and martensite.

Mosaic ceramic art pattern with noble, elegant features, it is a unique form of art creation in ancient Greece and the ancient Rome period has been loved by artists and created a lot of classic large-scale exterior mosaic ceramic art works. Small size square mosaic ceramic as the basic raw material for the creation of large exterior mosaic art, it directly affects the quality of the work created by the artist, so these ceramic mosaic ceramic materials need to undergo rigorous inspection to meet the needs of the artist’s high-quality art creation. However, small size multi-color square mosaic ceramics are different from ordinary large target ceramics, they have the characteristics of small size and easy reflection, currently mainly using manual inspection, the existing automatic inspection methods have the problem of low efficiency and accuracy, cannot meet the needs of artists for the quantity and quality of mosaic ceramics. To solve these problems, this paper proposes a new convolutional network-based fast nondestructive testing method for detecting square mosaic tiles. The detection method is based on the convolutional neural network YOLOv5s model, and by introducing the AF-FPN module and the data enhancement module, the method further improves the recognition performance of the model relative to the original YOLOv5s model and achieves the fast detection of surface defects on square mosaic ceramics. The experimental results show that the detection method for small size multicolor square mosaic ceramic tile surface minor defects detection rate of up to 94 % or more, a single square mosaic ceramic detection time of 0.41 s. The method takes into account the detection accuracy and speed, can be fast and accurate screening of high-quality, defect-free small size multicolor square mosaic ceramic, to meet the artist’s requirements for high-quality mosaic ceramic raw materials Quality and quantity requirements, to ensure the quality of the creation of mosaic art patterns, to better show the charm of the mosaic art patterns role. At the same time, the method can not only be applied to the detection of mosaic ceramics, the method can also be applied to have a similar small volume, easy to reflect the characteristics of small target object defect detection.

This study aims to manufacture sandwich composite structures consisting of fully fiber-reinforced composites and then to investigate experimentally and numerically the impact and compressive strength and damage mechanisms of these structures for different cell and core types. To achieve this, firstly, composite sandwich plates with triangular, square and rectangular cell structures were manufactured. Low-velocity impact tests were run on sandwich structures with these three different cell geometries and the effect of cell shape on impact strength was determined. Although the maximum contact force of the square structure under impact load was smaller than the maximum contact force of the triangular and rectangular specimens, the specific contact force was 15.52 % greater than the triangular specimen and 16.29 % greater than the rectangular specimen. Then, the specimens with square, egg box and lattice core types were manufactured and compression tests were performed. The specific peak load value for square specimens was 33.2 % greater than that of egg box specimens and 78.1 % greater than that of lattice specimens. In the numerical study, the experimental results were confirmed by applying the progressive failure analysis with the LS-DYNA finite element program.

Friction stir spot welding (FSSW), which is one of the joining methods, is an interesting solid state joining process. In this experimental study, the joining of AA7075, which is the one of the Al-based alloys, with the FSSW method was conducted. Firstly, the microstructural inspections were performed by helping an optical microscope. Second, a numerical simulation study was performed using SolidWorks and ANSYS software. Therefore, these data were evaluated with modeling for understanding the events in zone of FSSW center. Thus, it could be contributed to understand the complex thermo-mechanical joining process period. The present simulation primarily aims to explain the effect of a set of process such as parameters and tool geometry on the workpiece couples. Johnson–Cook damage criteria model was selected to obtain the stress distribution on the workpiece couples consisting of AA7075. The model also showed that temperature and stress did not exhibit much appreciable change on flow with the change of the tip profile. As a result, it was found that tool rotation speed and tool plunge depth are highly effective on both microstructure and numerical modeling properties, apart from the tool geometry, which is one of the welding parameters.

Multi-cell columns inspired by diatom algae have been examined regarding crashworthiness. Crushing simulations have been conducted for AA2024-T351, B1500HS-O25, and a combination of these materials. The highest specific energy absorption and lowest peak crushing force value were obtained with a homogenous AA2024-T351 column. Single and multi-objective optimization studies have been conducted with this column to find the best design. This design could be used in crash-box-like structures in automotive design.

Honeycomb sandwich composites play an important role in the aviation structural components, especially in aircraft radomes. Due to the multiple production processes, failure of the honeycomb sandwich composite usually occurs. This would affect the working stability of mechanical components made mainly of the honeycomb structural materials. In the present work, collapse failure of the honeycomb sandwich composite in an aircraft radome was investigated. The observation and analysis results show that the failure mode of the honeycomb structure is compression instability failure. There are a lot of pore defects in some local bonding areas of the honeycomb structure, forming a weak bonding area. In the process of curing and pressurization, debonding occurs at the adjacent honeycomb cells near the weak bonding area, forming a cracking band and resulting in the decrease of the stiffness and the instability failure under pressure. The work would provide reference information for the application of honeycomb sandwich composites in mechanical equipment.

In this article, a new prairie dog optimization algorithm (PDOA) is analyzed to realize the optimum economic design of three well-known heat exchangers. These heat exchangers found numerous applications in industries and are an imperative part of entire thermal systems. Optimization of these heat exchangers includes knowledge of thermo-hydraulic designs, design parameters and critical constraints. Moreover, the cost factor is always a challenging task to optimize. Accordingly, total cost optimization, including initial and maintenance, has been achieved using multi strategy enhanced PDOA combining PDOA with Gaussian mutation and chaotic local search (MSPDOA). Shell and tube, fin-tube and plate-fin heat exchangers are a special class of heat exchangers that are utilized in many thermal heat recovery applications. Furthermore, numerical evidences are accomplished to confirm the prominence of the MSPDOA in terms of the statistical results. The obtained results were also compared with the algorithms in the literature. The comparison revealed the best performance of the MSPDOA compared to the rest of the algorithm. The article further suggests the adaptability of MSPDOA for various real-world engineering optimization cases.

This study was conducted to understand the creep behavior of two oxide dispersion strengthened alloys containing Zr as the alloying addition by performing indentation creep tests at room temperature. The oxide dispersion strengthened alloys were Fe–8Ni– x Zr ( x  = 1 and 4 at.%, i.e., Zr-1 and Zr-4 alloys, respectively), which had been previously fabricated by mechanical alloying; followed by consolidation via equal channel angular extrusion at 1000 °C. The indentation tests were conducted under a maximum load of 100 mN with the loading rates at 300 and 400 mN min −1 . The hardness was calculated by the Oliver–Pharr method, and the creep properties, such as the creep displacement, creep strain rate, creep stress, and stress exponent n , were determined. The results showed that the Zr-4 alloy was harder than the Zr-1 alloy. However, the creep resistance of the Zr-1 alloy was better than that of the Zr-4 alloy. It was further demonstrated that both the hardness and creep resistance depended on the loading rate. Moreover, a possible creep mechanism was proposed. Although the tests were performed at room temperature, they can provide insight into the effect of an oxide dispersion strengthened alloys microstructure on creep at higher temperatures.

The development of aluminum (Al) based composites has been an interesting subject to sustain technological developments in the defense, automotive, and aerospace industries. In this study, the microstructure, mechanical, and tribological performances of hybrid Al composites reinforced with fixed ratio (4 %) graphite (Gr) and two different reinforcement materials such as tungsten carbide (WC) and aluminum oxide (Al 2 O 3 ) at different ratios were investigated. The impact of hybrid reinforcement and its ratios on the relative density value and hardness performance were investigated. The results of three different loads (1, 2, and 3 N) and three different sliding distances (200, 300, and 400 m) on wear performance were analyzed using Taguchi’s L 18 experimental design. High relative density (94.39 %) and hardness (74.26) values were achieved by hot pressing. It has been determined that hybrid reinforcements have positive effects on wear performance. The lowest SWR value was recorded as 7.82 × 10 −5  mm 3 /N.m in composite no Al-6. As the applied load raised, the friction coefficients decreased. On the other hand, the sliding distance and the increased applied load caused the temperatures to rise. With Al–4Gr/WC–Al 2 O 3 composite material, a new AMMC has been presented to the literature, which has remarkable hardness and wear properties, and can show better ductility and machinability compared to equivalent materials.

New alloy materials developed to meet the increasing technological needs of people come into our lives with some difficulties in terms of machinability. New cooling and lubrication techniques have been developed to facilitate the workability of such difficult-to-process materials and protect the world ecologically and the quality of the produced product. The workpiece used in this study, Vanadis 10 SuperClean, is a high vanadium alloyed powder metallurgy tool steel offering a unique combination of excellent abrasive wear resistance in combination with a good chipping resistance. The present study investigated the effects of dry, cryo, and CryoMQL cutting conditions on cutting tool vibration amplitude, cutting temperature, surface roughness, tool wear, and tool life in turning of Vanadis 10 tool steel used in the automotive industry. The experiments were performed using TiCN/Al 2 O 3 /TiN coated cemented carbide tools and cutting parameters as the constant depth of cut (1 mm), feed rates (0.08, 0.1, 0.12 mm rev −1 ), and cutting speeds (80, 100, 120 m min −1 ). The results obtained from experiments showed that spraying liquid nitrogen into the cutting zone provided significant improvements on cutting temperature, tool wear, cutting tool vibration amplitude, and surface roughness. The best results in terms of all output were achieved in the CryoMQL cutting environment. CryoMQL environment has reduced surface roughness up to 65.03 %, flank wear 56.99 %, cutting temperature 32.77 %, and cutting tool vibration amplitude up to 42.76 % compared to dry machining.

The Taguchi optimization method was used to optimize waste and natural different components such as waste marble dust, expanded perlite, perlite aggregate size, cement, and molten tragacanth in the production of new insulation composite material. Compressive strength, thermal conductivity, abrasion loss, and water adsorption properties of the developed composite material were investigated. Taguchi’s standard L18 array was chosen for optimization of these four components with different levels. Response plots were created using the Taguchi and the optimum test condition was determined. The insulation composite material with the best thermal and mechanical properties was obtained under the condition of waste marble dust (1), expanded perlite (1), perlite aggregate size (1) and molten tragacanth (1). In addition, using the anova (Analysis of Variance), percentage impacts on the mechanical and thermal properties of the test parameters were determined. Statistical values obtained from anova and mathematical models are developed by using multi-linear regression method. It was found that the mathematical model and the experimental results were quite compatible. The optimum test conditions detected were verified by confirmation experiments. Confirmation experiment results were obtained between 99.9 % confidence interval values.