Volume 63, Issue 2

IN-738 turbine blade samples, deteriorated after long term service at high temperatures, were solution heat-treated at two temperatures, 1398 K and 1473 K, for 7.2 ks. Subsequently, the samples were cooled down in different atmospheres, in air and in furnace, for the purpose of studying the effects of different cooling media (rates) on the restored microstructures. Following this, the samples were aged at 1118 K for 43.2 ks and 86.4 ks in order to determine the characteristic of re-precipitated gamma prime particles. A scanning electron microscope (SEM) and ImageJ analysis software were used. The results show that the cooling in air provided gamma prime particles re-precipitating in spherical shape while the cooling in a furnace resulted in coarse gamma prime particles re-precipitating in irregular shape. The samples solutionized at 1398 K for 7.2 ks cooled down in air and then aging at 1118 K provided bimodal microstructure, while the sample solutionized at 1473 K for 7.2 ks, followed by air cooling and aging at 1118 K generated unimodal γ ’ precipitation in spherical shape. Cooling in a furnace provides coarse γ ’ recipitated particles in more irregular shape for the both solutionizing temperatures studied here. Cooling in a furnace provides coarse γ ’ precipitated particles in more irregular shape for the both solutionizing temperatures studied here.

This paper is about the theoretical and experimental characterizations of the torsional vibration behavior of circular and rectangular cross-sectional arc springs. Firstly, the dynamic behaviors of arc springs with different cross-sectional wire profiles designed for a dual mass flywheel are modeled by mathematical formulations. After that, experimental tests are performed to verify these models and it is observed that the stiffness characterizations are in good agreement with experimental results. Lastly, the masses of two different arc springs are compared by regarding the same vibration stiffness criteria and it is demonstrated that the rectangular wire provides an arc spring with a 9.44 vol.-% lighter structure. Thus, the outcomes of this paper can be good references for the manufacturer about the numerical and experimental characterization of dual mass flywheel springs, especially for rectangular wire arc springs.

This article presents results of the study on the dependence of the structural-phase state of alloys based on Ti-12.52Al-43.08Nb system (wt.-%) on the temperature of spark plasma sintering. It has been established that spark plasma sintering of Ti-Al-Nb alloys under the temperature of 1500 °C resulted in melting the aluminum component of the mixture that, in turn, negatively affects the quality of ready products. It has also been shown that stepping up the sintering temperature from 1000 °C to 1300 °C leads to increasing volume fraction of O-phase up to 49.63 % due to rapid precipitation of O-phase from B2-phase and Ti 3 Al-phase. It has been revealed that intermetallic composites obtained under the temperature of 1300 °C are characterized by a dominant two-phase В2+О structure which is more suitable for strengthening sorption properties of hydrogen-storing materials based on Ti-Al-Nb.

In this study, the maximum tensile shear load bearing capacity and fracture modes of resistance spot welded DP1200 steel were investigated, and the tensile shear properties of the joints were evaluated. The effects of different welding parameters on tensile shear properties, fracture modes, microstructure, microhardness, and heat affected zone softening were examined. Weld processes were performed by using 2 to 6 bar electrode pressure as well as 5 and 7 kA weld currents. The microstructure of resistance spot welded materials was evaluated, and the hardness profiles were determined. Experimental results showed that welding current and electrode pressure had a significant effect on the load-displacement characteristics of DP1200 welds. Three different fracture modes were observed in the tensile shear loads. It was also observed that the expulsion had a negative effect on the tensile shear properties.

In the present work, different ultrasonic C-scan approaches were used to evaluate Carbon Fiber Reinforced Polymers (CFRP) submitted to impacts of low energy, in order to evaluate their effectiveness for the detection and characterization of small defects. In particular, as to the question how useful could be the air-coupled C-scan approach, using low frequencies, for in-service application. For that goal, several samples with different stacking sequences and thicknesses were impacted with 1.5 and 3 J. Then, ultrasonic C-scan images were produced by immersion pulse-echo (in amplitude and time-of-flight (TOF)) and immersion through-transmission, and also by air-coupling through-transmission. The immersion C-scan images were produced using 5, 10 and 20 MHz probes and the air-coupled C-scan was made using two 400 kHz probes. The obtained images for the considered samples show that all used methods are able to detect the defects and give acceptable information about their size and shape. However, if the way of delamination evolving over thickness is of interest, the images by TOF should be used. As expected, good image resolution with sharp contour defects require high frequencies. Nevertheless, the air-coupled C-scan demonstrated similar capabilities to detect defects, with the advantage that the coupling medium is air, thus widening the range of applications, such as real-time damage monitoring of composite structures. As a disadvantage, the air C-scan system requires high power emission signals, and also great amplification of the received signals, to face the considerable attenuation in the air.

Seat frames in commercial vehicles generally consist of components such as foot brackets, seats, back, head restraints and fasteners. In addition to mechanical properties, comfort is another important parameter. This study aims to reduce the cost of a commercial vehicle by means of alternative materials and design changes in the passenger seat frame. For this purpose, three different methods were used to optimize seat back pipes: reducing the cross-section, using thinner sections in the seat frame via alternative material and making design changes in the foot brackets. In the methods applied, mitigation and cost reductions were achieved. The suitability of the design changes in the seat through geometric changes was confirmed by international ECE R14 test results and finite element method analyses.

During polymer extrusion there are a variety of situations in which the screwthread of the extrusion screw has an unlubricated metal-to-metal contact with the barrel wall. At the same time the screw coating is subjected to the highest loads. The combination of a secondary hardening cold work steel 1.2379 and a chromium nitride coating deposited by ARC-PVD, which is frequently used in polymer processing, is characterized and investigated. The characterization is done by metallographic examination, SEM and CLSM. The tests were performed on a pin-on-disk and a pin-roll test rig. Different roughness levels were tested on the pin-on-disk test, where massive differences in wear behavior were found. A hybrid surface structure is proposed to optimize the tribosystem. On the pin-on-disk test stand, rollers made of the same material pairing were tested. The test speed was varied to highlight differences and similarities between the tribological systems. A wear minimization of 50 % was achieved and the similarities between the tribological systems were highlighted. In addition, the investigations led to the development of a new model thesis which provides a reason for the development of stippling on the screw when processing polycarbonate.

The influence of metal inert-gas arc welding (MIG) on the corrosion behavior of 6061-T6 aluminum alloy in a simulated tropical marine atmospheric environment (related to high temperature, high humidity and high salt spray) were examined by dry-wet alternate immersion corrosion tests. The equivalent conversion was used to design the accelerated test time. The results show that in the initial stage, the intermetallic compound, rich in Fe, Si and Cu, had little influence on corrosion resistance in the heat-affected zone. For a corrosion time of 3 days in a tropical marine atmospheric environment, the corrosion rate of the welded joint increased rapidly, even reaching 3.5 times that of the base metal. Though the corrosion products had significant impact on slowing down the corrosion rate, as with the base metal, the corrosion rate of the welded joint was nearly double that of the base metal during the longest cycle period involving alternate immersion corrosion tests for 20 days.

In this paper, a new hybrid Taguchi salp swarm algorithm (HTSSA) has been developed to speed up the optimization processes of structural design problems in industry and to approach a global optimum solution. The design problem is posed for the shape optimization of a seat bracket with a mass objective function and a stress constraint. Objective function evaluations are based on finite element analysis, while the response surface method is used to obtain the equations necessary for objective and constraint functions. Recent optimization techniques such as the salp swarm algorithm, grasshopper optimization algorithm and, Harris hawks optimization algorithm are used to compare the performance of the HTSSA in solving the structural design problem. The results show the hybrid Taguchi salp swarm algorithm’s ability and the superiority of the method developed for optimum product design processes.

In this research, the effect of adding graphene-based aerogel ((G)A) nanoparticles on the tensile and fatigue behavior of the epoxy polymer was investigated. Specimens of nanocomposites were prepared by adding 0.05, 0.1, 0.2, 0.5, 1, and 2 wt.-% (G)A nanoparticles to the epoxy polymer. Tensile tests revealed that the 0.1 wt.-% graphene-based aerogel/epoxy ((G)A/E) nanocomposites had the highest increase in tensile strength with 19 % growth compared to neat epoxy. Also, the tensile modulus increased by 15 % in the 0.5 wt.-% (G)A/E nanocomposites. A substantial improvement in fatigue life of the epoxy polymer was observed on adding 0.1 wt.-% (G)A nanoparticles. For instance, the fatigue life of (G)A/E nanocomposites improved by 236 % at a maximum stress of 35 MPa compared to the neat epoxy. Fractography in failure analysis of the test samples showed that the placement of (G)A porous nanoparticles on the epoxy polymer with crack twist or crack tilt prevent the formation of large and catastrophic cracks, resulting in delaying the fatigue failure.

The present analysis was aimed to identify the properties of Al 2024 composite reinforced with lithium and silicon nitride to make it applicable for automobiles, sports and aerospace applications. An effort was made to reduce the density and increase the hardness and impact properties of aluminum 2024 matrix with individual and multiple reinforcements using the double casting method under non-reactive environment. Aluminum alloy matrices with lithium, silicon nitride and the combination of both were fabricated. The microstructure, density, hardness and impact strength properties of the fabricated aluminum metal matrices were analyzed. The microstructure study reveals the uniform dispersion of reinforcements in the matrix alloy. From the results, it is understood that the hardness and impact toughness increase with the addition of silicon nitride. Density is reduced with the addition of lithium as reinforcement. When both reinforcements were added in the matrix, it was observed that there was an increase in hardness and impact strength of the composites with decrease in density of the metal matrix composite making it suitable for light weight and high strength applications.

The use of adhesive joints is increasing in aerospace, aviation, automotive, construction and marine industry due to their easily applicable properties, low-costs and light weights compared to traditional jointing methods such as bolts, rivets, welding and soldering. Due to the high fatigue strength, resistance to seawater corrosion and light weight, aluminum alloys, with their high satiety, fracture strength, light weight, high specific strength and good dimensional stability and other properties, glass fiber reinforced composite materials have widespread uses.

The present study was carried out to analyze the effect of process parameters during EDM machining of AA7075-10 wt.-% TiO 2 aluminum matrix composite (AMC). The composite was produced through stir casting. The EDM process parameters such as the electrode material (Cu, Br, EN-8), pulse current (5, 10 and 15 A), pulse ON time (300, 600 and 900 μ s) and pulse OFF time (30, 60 and 90 μ s) were chosen to study the effects on material removal rate, surface roughness and the electrode wear ratio. The experiment was carried out as per L27 orthogonal array based on Taguchi’s design of experiments. Signal-to-noise ratio and analysis of variance were used to identify the contribution of each input parameters on the output responses of the EDM process. The experimental results shows that pulse ON time and pulse current are the most significant factors for the material removal rate; pulse ON time and electrode material are the most influencing parameters for surface roughness and the electrode wear ratio.

Chitin and chitosan as green and active biomacromolecules were extracted from local seafood waste (shrimp shells). The extraction was carried out by a soft chemical process, followed by structural characterization (FTIR, XRD, viscosity average molecular weight M̅ v ), thermal stability by TGA, and antibacterial tests. FTIR and XRD spectra confirmed the chemical structures of the extracted chitin and chitosan which were similar to the commercial ones. The chitin and chitosan had an average viscosimetric molar weight of 232.21 kDa and 41 kDa, respectively. The chitosan had a high deacetylation degree (DD = 71 %) and low cristallinity index (Icr = 68.3 %); compared to chitin, which exhibited a lower deacetylation degree (DD = 24.27 %), higher thermal stability and higher cristallinity index (I cr = 87.55 %). A bacteriostatic effect of chitin was observed in the gram-negative bacteria, Escherichia coli, Salmonella typhimurium. Chitosan exhibited a bacteriostatic effect on all bacteria tested, except Salmonella typhimurium.