Volume 64, Issue 4

The effects of different soaking times and cycles of deep cryogenic treatment on the microstructure and mechanical properties of Co 28.5 Cr 21.5 Fe 20 Ni 26 Mo 4 medium entropy alloys were studied. The results show that the maximum hardness and compress strength were 364 HV and 3153 MPa after cryogenic deep treatment for 8 h, which were increased by about 9.97% and 33.32%, respectively. The maximum hardness and compressive strength were 375 HV and 3039 MPa, which were increased by about 13.29% and 28.50%, respectively, after three deep cryogenic cyclic times. The reason is that μ phase is rich in Mo, and Mo element has high strength and hardness. After deep cryogenic treatment, the agglomeration of μ phase in the alloys was improved, the distribution of μ phase was more uniform, the content of μ phase was increased, and the content of Mo element in the μ phase was increased, so that the strengthening effect of μ phase was enhanced.

The AISI M2 steel has been treated by solid boriding between 1123 and 1273 K for an exposure time of 2–8 h. In these circumstances, a bilayer constituted by FeB and Fe 2 B has been formed with interfaces nearly flat. The tribological behavior and decohesion resistance of boride coatings were studied by using the following characterizations: (Rockwell-C cohesion, pin-on-disc and wear scratch tests). The modeling of process kinetics was undertaken based on two different approaches (the mass balance equations and the integral method). The assessed values of boron activation energies in FeB and Fe 2 B arising from the two models were nearly similar. In addition, the predicted layers’ thicknesses at 1243 and 1273 K during 10 h were concordant with the experimental values.

This study aims to characterize and evaluate the effects of graphene nanoplatelets (GnPs) added to the epoxy matrix and the fiber stacking sequence on the mechanical and impact responses of carbon/aramid hybrid composites. For this purpose, Aramid/Glass/Aramid and Glass/Aramid/Glass stacking sequences as well as full Aramid and Glass fiber configurations were used in an epoxy matrix with various contents (0.1, 0.25, 0.5 wt%) of GnPs. Tensile and flexural tests were conducted per mechanical characterization and low-velocity impact (LVI) tests with 30 J impact energy were performed by a drop-weight impact test. According to results, aramid fiber location has a significant effect on the peak load values, absorbed energy, and displacement of the hybrid composites. In addition, the inclusion of 0.25 wt% GnPs into the epoxy matrix increased the LVI properties of pure glass and hybrid fiber-reinforced composites. However, the incorporation of GnPs into the epoxy matrix caused a deterioration in the LVI properties of the aramid fiber-reinforced composite plates. Moreover, the best increase in the mechanical properties of pure and hybrid fiber-reinforced composites was obtained by adding 0.1 and 0.25% wt% GnPs into the epoxy matrix.

In this study, B 4 C and SiC hybrid reinforced Al–Cu–Mg–Si alloy Matrix composites were fabricated using a microwave sintering technique at a sintering temperature of 550 °C for 60 min. In the produced hybrid composites, while the B 4 C ratio was kept constant (3 wt%), SiC was used in four different amounts (3, 6, 9, and 12 wt%). In these produced hybrid composites, as a result of microwave sintering, thanks to the high microwave absorption of SiC, the porosities closed at a rate of 36.65–40.90%. In 3, 6, 9, and 12 wt% SiC reinforced composites, the microhardness of 100.1, 106.8, 114.4, and 117.2 HV 0.05 were achieved, respectively. Due to agglomeration increasing with SiC reinforcement rate, delamination wears increased in 12 wt% SiC reinforced hybrid composite. As a result, the lowest specific wear rate was measured as 0.3374 × 10 −3  mm 3 ·(Nm) −1 in the 3 wt% B 4 C+9 wt% SiC reinforced sample.

As a result of polymer materials development and the use of additive manufacturing technologies, gear wheels made of polymer materials are becoming widespread in many areas of the industry. In recent years, determining the dynamic behavior of polymer gears has gained significant importance because it is desired to carry more loads and operate at higher speeds. Since it is one of the most critical factors affecting dynamic behavior, tooth stiffness should also be determined. In this study, the single-tooth stiffness (STS) of polymer gears with symmetrical and asymmetrical profile was measured experimentally with a unique test setup. Force was applied to three different points on the tooth, and the resulting deflection was measured with the help of linear variable differential transformer and a high-speed camera. Using the obtained deflection values, STS of the polymer tooth was calculated depending on the pressure angle. The experimental results are also compared with the finite element model created, and it is found that the results are matched well. As a result of the study, it is determined that the drive-side pressure angle of the polymer gear increased from 20° to 32°, and the tooth stiffness increased by approximately 10.8%.

The modernization in automobile industries has been booming in recent times, which has led to the development of lightweight and fuel-efficient design of different automobile components. Furthermore, metaheuristic algorithms play a significant role in obtaining superior optimized designs for different vehicle components. Hence, a hunger game search (HGS) algorithm is applied to optimize the automobile suspension arm (SA) by reduction of mass vis-à-vis volume. The performance of the HGS algorithm was accomplished by comparing the achieved results with the well-established metaheuristics (MHs), such as salp swarm optimizer, equilibrium optimizer, Harris Hawks optimizer (HHO), chaotic HHO, slime mould optimizer, marine predator optimizer, artificial bee colony optimizer, ant lion optimizer, and it was found that the HGS algorithm is able to pursue the best optimized solution subjecting to critical constraints. Moreover, the HGS algorithm can realize the least weight of the SA subjected to maximum stress values. Hence, the adopted algorithm can be found robust in terms of obtaining the best global optimum solution.

A significant amount of environmental pollution is caused by oil refinery industries in the form of spent alumina catalyst (SAC) waste generated during the process. This waste causes various detrimental effects on human health. In this study, an effort has been made to consume the SAC in the fabrication of aluminum-based composite materials via the friction stir process (FSP). An X-ray diffraction image of the SAC powder used in this work confirms the occurrence of Al 2 O 3 , Fe 2 O 3 , SiO 2 , and CaO phases. These hard-phase materials form the basis for SAC to be used as reinforcement content with the aluminum alloy. The FSP is used to create the composite material. It is evident from the scanning electron microscopy image of the Al/SAC composite developed by the FSP technique that fair distribution of constituent ingredients is attained during the process. The incorporation of SAC contents in the aluminum alloy results in remarkable enlargement in tensile strength and hardness of the composite material. The Al 2 O 3 , Fe 2 O 3 , SiO 2 , and CaO phases of SAC showed a considerable effect on thermal expansion and corrosion weight loss of the composite.

In this study, three different powder (alumina, boron, and ekaboron III) combinations were coated on the austenitic stainless steel surface by the PTA welding method. The microstructure and wear resistances of the composites coating obtained under different parameters and coating layer were comparison and analyzed. The microstructure, microhardness, and abrasion resistance of different powder coatings were compared and systematically investigated. It has been found that successful bonding is present in almost all of the coatings made and the microstructure of all sample were different. However, the highest hardness values (alumina, ekaboron III and boron) were measured as 1133, 1154, and 1220 HV, respectively. Trying to find the most suitable coatings by comparing different commonly used powders has been the main goal in this study.

In the micro-hardness range of the load, the measurement is complicated by the occurrence of the Indentation Size Effect (ISE) – the measured value of the micro-hardness is affected by the value of the applied load. The paper aims to study the influence of the automatic testers on the character type and size of the ISE. Ten testers and five standard reference blocks were involved in the “round-robin test”. Parameters of the ISE were evaluated using Meyer’s, Hays–Kendall, and PSR methods and also by statistical methods (ANOVA, t -test, regression, and cluster analysis). Despite the assumptions, a statistically significant impact of the hardness tester was found not only on the measured value but also on the character and size of ISE.

In this study, a boron steel bumper beam’s crashworthiness performance with three different hardness values and six different bumper beam designs with tailored properties was compared in passenger safety. Peak crushing force and energy absorption values of the beams were examined by frontal impact simulations. Minimum peak crushing force value was obtained with the O25 heat treated beam, the front side O25 and rear side T500 heat treated beam and the front side T500 and rear side O25 heat treated beam. The Front side T25 and rear side O25 heat treated beam gave the highest energy absorption value. Single and multi-objective optimization studies were conducted to maximize energy absorption and minimize peak crushing force for this beam with tailored properties. The optimal beam improved the impact performance of the structure. Therefore, this beam can be used in front bumper beam design to improve passive safety.

The results tested by the impact-echo method of the small-size short cylinder/circular tube structure were fundamentally different from that of the large-size long one. This phenomenon cannot be described by the existing calculation formulas. To modify the classical calculation formula, finite element models of various sizes of small-size short cylinder/circular tube structures, including 80 cylinders and 125 circular tubes, were established. Modal analysis frequency was compared with numerical simulation of impact-echo frequency under partial working conditions. In addition, the impact-echo frequency of whole working conditions was counted for later analysis. The impact-echo frequency correction formulas of the small-size short cylinder/circular tube considering the model length and the cross-sectional size of the cylinder/circular tube were proposed. Moreover, their reliabilities were verified through tests. The results showed that the impact-echo frequency of the small-size short cylinder structure increased linearly with the increase in diameter, decreased with the increase in length, whereas the relationship among frequency, outer diameter, and wall thickness of the circular tube component was complicated. Moreover, the modal of the whole member was excited rather than the free modal of the cross section of the large-size cylinder/circular tube when the small-size short one was impacted.

In order to increase the lap shear strength and weldability of aluminium alloy (Al6061), spot welding is done in lap configuration with an interlayer of graphene nano-platelets (GNPs). The GNPs are bonded using polyvinyl alcohol (PVA) and drop-casted on one of the mating surfaces of the lap joint before the resistance spot welding process. The experiment is carried out using different welding currents and time cycles at a constant load. It was found that the processing parameters and the presence of GNP interlayer play an important role in the performance of the lap joint. An increase of approximately 60% in the lap shear strength was observed with GNP interlayer at optimum processing conditions. Interfacial–microstructure characterisation was carried out across the fractured surface of the lap joint by using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). An increase in hardness, a change in nugget diameter and the mode of failure were observed in the presence of the GNP interlayer. A detailed analysis of the possible weld strengthening mechanisms is included in this article.

Aluminum matrix composites focus primarily on improving mechanical properties such as hardness and wear, however, the softness of the aluminum matrix and thermal coefficient difference between matrix and reinforcement adversely affect these properties. In the present paper, the wear properties of aluminum matrix composites including different amounts of reinforcement were investigated before and after the shot peening process which was used for decreasing the harmful effects as mentioned. The experimental studies clearly reveal that shot peening, which is a mechanical surface treatment and generally used for improving fatigue resistance of materials, has a beneficial effect on the poor wear behavior of metal matrix composites. Obtaining results also indicate that the microhardness is improved greatly up to a certain depth by shot peening due to the higher dislocation density/microstrain which is evidenced with the X-ray diffraction tests.

Drilling is one of the critical processes in machining. High cutting forces that occur during drilling cause energy loss and wear of tools. Therefore, optimization of drilling parameters plays a significant role. The effects of drilling parameters on thrust force on AISI 2080 steel was investigated in this study. Drilling conditions were optimized to minimize the thrust force (Fz) by the Taguchi method. Experiments were conducted using two parameters (feed rate and cutting velocity) with three levels. A mathematical model for the Fz was obtained by the response surface methodology. The effect ratio of parameters on the results was determined by the analysis of variance. Optimum cutting parameters had been 30 m.min −1 for cutting velocity and 0.05 mm.rev −1 for feed rate. In addition, the results obtained according to the regression model generated and the results estimated by the Taguchi method were compared with the actual experimental results. Considering the error rates, it is observed that both methods were usable.