Volume 66, Issue 3

The effects of temperature and strain rate on the deformation microstructure and hardness of Al–Zn eutectoid damping alloy was systematically investigated. The results show that the deformed alloy is mainly composed of eutectoid structure with η -Zn distributing on α -Al matrix. There are two forms of η -Zn particles in the eutectoid structure of the deformed alloy. The first type of η -Zn particles ( η -Zn I ) have relatively large sizes and display irregular morphology; another type of η -Zn particles ( η -Zn II ) have relatively small sizes and are characterized by dispersion distribution. There exist predominant η -Zn I particles at lower temperature and higher strain rate while dominant η -Zn II particles at higher temperature and lower strain rate. The hardness of the Al–Zn eutectoid damping alloy shows an overall rising trend with increase in temperature and decrease in strain rate. In particular, the highest hardness values (up to 113.07 HB) are obtained at 648 K/0.01 s −1 .

This study investigates the influence of modification on the microstructure and properties of Mn–Si–Cr alloy steel. The results indicate that the as-cast microstructure of Mn–Si–Cr alloy steel is composed of black acicular bainitic ferrite lath and white retained austenite. The microstructure of the alloy steel changes to martensite, austenite, and carbide after quenching and partitioning treatment. After rare-earth magnesium modification and compound modification, the as-cast microstructure of Mn–Si–Cr steel becomes more refined and displays a more regular arrangement. Furthermore, the martensite and austenite grains in the modified samples show refinement, and the arrangement of martensite is more systematic. Additionally, the amount of austenite decreases, and the amount of carbides increases after quenching and partitioning heat treatment. In comparison with the unmodified samples, the modified samples show negligible changes in hardness. However, the impact toughness of modified quenched and partitioned steel increases by 20 %. Moreover, the wear resistance of compound modified quenched and partitioned steel is 38 % higher than that of the unmodified sample. The compound modified sample steel exhibits excellent wear resistance and comprehensive mechanical properties.

Q355 steel with Cu interlayer was bonded by transient liquid phase diffusion bonding (TLP-DB) at different bonding temperatures, and good bonding joints were obtained. The joints were characterized by optical microscopy, scanning electron microscopy and mechanical properties. The results show that there is a bending phenomenon caused by the difference of element diffusion at the bonding interface at the bonding temperature of 1050 °C. With the increase of the bonding temperature, the diffusion of Cu element plays a role in refining the grain, but with the increase of the bonding temperature, it will also lead to the overgrowth of the grain; At the bonding temperature of 1050 °C, there are obvious mutations in the diffusion of Cu and Fe elements, but the increase of the bonding temperature has a good effect on the interdiffusion of the elements. The mechanical properties test showed that with the increase of the bonding temperature, the hardness, shear strength, and impact toughness at the center of the joint increased first and then decreased, and all reached the maximum at 1100 °C. The electrochemical performance test showed that with the increase of temperature, the corrosion resistance of the joint also increased first and then decreased.

In this study, automotive in sector use STRENX 700 CR and DP 800 steels were joined by resistance spot welding using medium frequency direct current. Some parts were joined under atmospheric conditions, while others were joined by applying regional preheating to their heat-affected zones before welding. The design, manufacturing, and adaptation of the preheating system to the welding machine were carried out as part of this study, considering it as a new system. After the joining process, nondestructive and destructive tests were performed on resistance spot welding connections between STRENX 700 CR and DP 800 steels. Hardness tests revealed that the preheating applied to the heat-affected zones before welding reduced the hardness of the weld metal by approximately 8 %, while the microstructure analysis showed that the regional preheating increased both the weld metal and the heat-affected zones width. The tensile-shear strength increased by about 7 %, and the cross-tension test strength increased by about 5 % with the preheating applied to the heat-affected zones before welding. In both the tensile-shear and cross-tension tests, all failures occurred in the form of button shearing from the heat-affected zones. The regional preheating treated specimens showed the highest fatigue life, with an average of 947,632 cycles.

The corrosion occurring in hoisting ropes used in transport machinery, directly and indirectly, significantly damages the global economy every year. The aim of this study is to investigate the behavior of different types of steel wire hoisting ropes used in cranes, ships, and ports, regarding their resistance to corrosion through the method of stress corrosion cracking and to determine which types of steel ropes should be utilized in environments exposed to severe corrosion. First of all, hessian and steel core ropes were selected from 6 × 19 Standard, 8 × 19 Seale, and 6 × 36 Warrington Seale rope groups of the same diameter. Prestress corrosion tests of the ropes were carried out based on the ASTM G49 standard, with the prestress corrosion test device designed and manufactured in accordance with different rope types. The results obtained by performing appropriate treatment methods against corrosion, such as hot-dip galvanizing and painting with zinc epoxy primer, were compared with the test results of ungalvanized ropes. Thus, the degree improvement against corrosion was determined.

In order to obtain a Al 2 O 3 /Al composite with high strength, the Al 2 O 3 generated in situ is served as reinforcement. The ball milling is used to flake pure Al powders. The Al 2 O 3 /Al composite with flaked Al powders is obtained by vacuum hot pressing sintering. The effect of the flaked Al powders on the distribution of Al 2 O 3 generated in situ is studied. The hardness and tensile properties of Al 2 O 3 /Al composite are studied. The results show that the dehydration temperatures of boric acid in powder mixtures with the flaked Al powders and with the spherical Al powders are 119 °C and 128 °C, respectively. During sintering stage, the Al 2 O 3 is generated in situ . Compared with the Al 2 O 3 /Al composites with the spherical Al powders, more Al 2 O 3 are generated in Al 2 O 3 /Al composites with the flaked Al powders. The hardness and ultimate tensile strength of Al 2 O 3 /Al composite are higher than those of pure Al alloy.

It is aimed to examine the effect of welding parameters on cruciform welded joints. Armor steels are used in military applications such as tracked and wheeled armored vehicles. These steels are quenched and tempered steels and have high yield stress and hardness. Although the increase in carbon equivalent increases the ballistic level together with the hardness value, weldability decreases. Therefore, the welding parameters of these steels must be determined carefully. Before the welding, chemical analysis, macro examination, hardness test, tensile tests and ultrasonic examination were carried out to verify the material properties. After the verification tests, plates were welded with three different welding parameters to observe the changing of the mechanical properties. After the welding process, welded pieces were subjected to non-destructive tests to inspect the weld imperfections. After the inspection, welded specimens were subjected to hardness test, macro examination and tensile tests. In addition to these tests, weld penetration (WP) measurements were performed with a new assessment method. In this measurement method, unit of area takes into consideration instead of the unit of length. As a result, it is determined that with the increasing welding parameters although WP increase, hardness values in heat affected zone decrease.

Different types of plates are available to allow insertion of screws for internal fixation of long bone fractures. The aim of the study was to determine the effect of the insertion of screws at different angles on a long bone to the pull-out strength. Using 3D printed bone models, we tested the pull-out strength of screws in long bones at insertion angles between 0 and 40° with both finite element analysis and on printed models experimentally and compared the results. Test samples and cortical screws used were modeled with SolidWorks software and analyzed with Ansys software. As the screw insertion angle increases, the pull-out forces on the test specimens increase from 61.14 ± 3.5 N at 0° to 273 ± 6.8 N at 40° with an exception of a small drop between 15 and 20° from 235.4 ± 6.2 to 233 ± 6.9 N. Both methods showed an increase in the pull-out strength of screws as the insertion angle increases. This might be applicable in the clinical practice of bone fixation. Further studies on plate and screw fixation are needed to complement the findings.

Crash boxes in vehicles are one of the passive safety measures that aim to reduce injury to passengers and damage to the vehicle during a collision. Their function is to absorb the mechanical energy resulting from a collision by deforming plastically. Considering human safety, not only the energy must be damped, but also the forces acting on the passengers must be controlled. This force control can be adjusted to some extent using trigger mechanisms. There is a wide variety of research on hole type triggers, but they concentrated on traditional shapes; unique or hybrid shapes have not been sufficiently tested. This study examined the effects of various hole profiles with equal areas on dynamic mechanical performances of Al 6063-T6 rectangular crash boxes. Four types of trigger shapes were formed: upward keyhole, downward keyhole, U-shaped, and S-shaped. The dynamic performance evaluation was carried out experimentally by testing five types of geometries, the fifth one being the geometry without any trigger. In addition, dynamic Finite element analyses were conducted and validated using the experimental data, with the aim of employing the Finite element models in future geometry improvement studies. The experimental results were interpreted with some common evaluation parameters: peak force, crash force efficiency, mean crash force, and total energy absorption. The downward keyhole profile generally gave the best results, while the lowest peak force was observed in the U-shaped profile.

Multi-pass surface friction hardening was employed to modify the microstructure and enhance the tribology characteristics of the Ti6Al4V alloy. The process was performed by reciprocated sliding a flat-head WC-Co cylindrical pin tool on the alloy surface under different applied loads of 350, 700, 1050, and 1400 N. The sliding was conducted at different speeds of 45, 90, 180, 360, 720, and 900 mm min −1 for 30, 60, 90, 120, and 150 passes, respectively. Based on the hardness test and microstructural characterization results, the applied load of 1050 N, the sliding speed of 900 mm min −1 , and the pass number of 60 (900-60 sample) were chosen as the optimum economic process parameters for the subsequent experiments. Performing surface friction hardening under the optimized conditions increased the surface hardness of the annealed sample from 350 HV 1 to 564 HV 1 showing an increase of about 60 %. Surface friction hardening was also found to substantially improve the tribology characteristics of the Ti6Al4V alloy. According to the obtained results, under the applied loads of 1 and 6 N, the wear rate and the average friction coefficient of the 900-60 sample were lower than those of the annealed one by 58 and 83 %, and 33 and 50 %, respectively.

In this study, we implemented two simple models to simulate the growth of the Fe 2 B layer on ASTM A307 steel through boriding. The first model considered steady-state boron diffusion, while the second model incorporated transient regime effects. In the steady-state model, the boron concentration profile within the Fe 2 B layer exhibited linearity. By correlating the boron chemical potential with the inward mass flux at the (Fe 2 B/substrate) interface, we confirmed the parabolic nature of layer growth. Both models were employed to determine the boron activation energies, yielding the same value of approximately 164 kJ mol −1 . Experimental validation of the two models was conducted under two additional boriding conditions (1323 K for 1.5 and 2 h). Finally, the simulated layer thicknesses matched with the experimental values.

As the power density of electronic devices increases, the requirement for heat sinks with enhanced thermal properties becomes imperative for advanced heat dissipation. Copper/diamond composites are next-generation heat dissipators with high thermal conductivities, yet fabrication of these composites requires high energy and complex instruments. In this study, copper/diamond composites are fabricated by electroforming. The sediment co-deposition process is modified to obtain uniform diamond particle distribution with tailorable volume fraction. Diamond particles were initially settled on the cathode surface outside the electrolyte, and then the setup was immersed in an acidic copper sulfate electroforming bath. Varying amounts (0–100 mg l −1 ) of thiourea are introduced to the electrolyte to enhance the matrix–particle interface. The gaps between diamond particles are filled with electrodeposited copper using optimized deposition conditions. The composite structure detaches from the cathode by itself after the production with desired shape and dimensions. The effect of operating conditions on cathodic polarization, composite microstructure, and thermal properties are investigated. Thermal conductivity of 49 vol.% diamond containing sample fabricated with optimized parameters exceeds 667 W m −1  K −1 . The increase in thermal conductivity and enhanced interface structure is attributed to the excellent void-filling ability of the optimized electrolyte.

Effective insulation is critical for traditional fishing boats because it helps to maintain the quality of the fish catch. Inadequate insulation can lead to significant economic losses for fishermen, as they may have to discard or sell the fish at a lower price. This study aimed to compare the thermal conductivity properties of three different insulation materials: Petung bamboo, polystyrene foam, and polyurethane foam. The experiment involved testing the density of the materials and conducting thermal conductivity tests. The results indicated that polyurethane foam is the best material for insulation because it has the lowest thermal conductivity value compared to laminated bamboo and polystyrene foam. The addition of more isocyanate mass fraction to the polyurethane foam material can increase its density and strength. This is because increasing the isocyanate concentration increases the cross-linking density of the foam, making it more durable and resilient. Moreover, higher density polyurethane foams exhibit lower heat conductivity, indicating better insulation qualities. This study highlights the importance of effective insulation to maintain the quality of the fish catch. The findings suggest that polyurethane foam, particularly with increased isocyanate concentration, is the most suitable material for insulation due to its superior insulation qualities.

In this research, we experimentally investigated how the shape of fittings affects the load-carrying capacity of miter joints in pultruded glass/epoxy composite frames. Specifically, three types of steel fittings – dovetail (D-shaped), H-shaped, and rectangular (U-shaped) were utilized to reinforce the miter joints in composite frames. Tension and compression tests were performed to assess the load-carrying capacity of these joint configurations. Additionally, finite element analysis (FEA) was employed to examine stress distribution patterns within the joint configurations, allowing us to make comparisons among the joint configurations in terms of their strength. The findings of the study demonstrated that all types of joint configurations successfully improved the joint strength, regardless of whether they were subjected to tensile or compressive loading conditions. Notably, H and D type steel fittings exhibited superior effectiveness in strengthening the adhesive miter joints when compared to U type steel fittings, particularly in tensile loading scenarios. Moreover, all types of steel fittings displayed promise as viable options for enhancing joint strength in compressive loading situations.