Volume 63, Issue 3

As fiber reinforced plastics (FRP) have been increasingly widely used, they may sometimes come into contact with several corrosive media simultaneously, for example, the condensate in the smokestack liners of coal-fired power FGD systems. To study the long-term performance and degradation mechanism of FRP in these complicated environments, an accelerated aging test of bromide epoxy vinyl ester (Br-VE) and its glass fiber reinforced composites (GF/VE) in a mixed acid solution(H 2 SO 4 , HNO 3 , HF and HCl) at three different temperatures(25, 55 and 80 °C) for 180 days was carried out. Weight changes, flexural properties, Fourier transforming infrared spectra (FTIR), dynamic thermal mechanical (DMA), macroscopic and microscopic morphology were investigated. Results showed that immersion temperature has important effects on the corrosion behavior of specimens. The long-term weight change behavior of GF/VE at normal temperature was in accordance with Fick’s second law, but deviated at higher temperature. Flexural properties of GF/VE declined more drastically than those of Br-VE at elevated temperatures. The T g of GF/VE decreased with rising temperatures. Results also indicted that Br-VE and GF/VE manifested varied degradation mechanisms when subject to the same mixed acid medium immersion. The degradation of GF/VE mainly involved plasticization, embrittlement, the hydrolysis of resin, an ion exchange between HF, H + and Si-O-Si or alkali metal of the fiber as well as the debonding of the resin/fiber interface.

The effect of stress corrosion on the mechanical properties of the coating in the zinc coating/304 stainless steel substrate system was investigated by three-point bending, slow strain rate tensile (SSRT) and nano-indentation tests. Studies have shown that fracture toughness was improved when the coating was thick but weakened when the coating was thin. At varied coating thicknesses (80 μ m, 160 μ m, 240 μ m, 320 μ m, 400 μ m), the decline rates of the fracture toughness were 77.48 %, 71.82 %, 66.67 %, 55.48 % and 51.52 %, respectively, and those for the critical strain of crack initiation were 94.97 %, 91.88 %, 88.42 %, 76.19 % and 74.33 %, respectively. In addition, simulations were made to analyze the crack propagation of zinc coating in coating/substrate system under tensile loading by ABAQUS, which proved the accuracy of the experiment.

When the hole-drilling method is used to measure residual stress, plasticity effects occur if the residual stress exceeds 60 % of the yield stress. Plasticity effects result in an overestimation of the residual stress as the hole-drilling method is based on the linear elastic behavior of materials. To overcome this problem, a simplified iterative method based on an existing iterative method and using the optimizer tools of the ANSYS program is proposed in this paper. The proposed method is verified through numerical and experimental studies. The numerical case study reveals that, for the case studied, the proposed method can achieve the same accuracy as the original iterative method and has a higher convergence ability. The experimental study demonstrates that the values of the maximum principal stress calculated using the American Society of Testing Materials standard is generally greater than the true values and that the error magnitude increases with an increase in stress levels. Using the proposed method, errors are reduced for the maximum principal stress while increasing slightly for the minimum principal stress. The proposed method has a high convergence ability; for the case studied, only two or three iterations are needed to achieve acceptable accuracy.

In this study, a compression spring fatigue problem arising from the galvanization process was investigated. Fatigue, crack initiation and growth of galvanized and non-galvanized springs manufactured from fully pearlitic high strength steel wires were investigated. According to the results, the galvanized compression springs exhibited a low fatigue life due to hydrogen embrittlement. Hydrogen embrittlement induced crack initiations formed under the galvanizing layer and adversely affect fatigue life. It was observed that local embrittlement on the outer surface of the spring wire causes crack initiations and disperses through the pearlitic interlamellar microstructure. Compared to non-galvanized and shot-peened specimens with the same surface roughness, compression springs, galvanized compression springs exhibited a 25 % reaction force loss at 50 000 cycles.

This study aims to investigate the relationship between wear resistance and microstructure of a hardfacing alloy Fe-C-Si-Cr-B-Ni system as well as investigating ways of improving the hardness of the hard facing layer through the addition of nickel to achieve a finer granular microstructure. Three hardfacing alloys are used for overlaying. Ferroboron (FeB) and Ferronickel(FeNi), are added to the massive wire during the welding process. A hardness test, microscopic characterization and wear analysis are carried out on the samples. The surfaces of the samples are examined using scanning electron micsoscope in order to better understand the wear mechanism. At room temperature, wear occurs through a combination of abrasive grooving and local delamination. Microstructure and hardness affect the wear resistance of the alloys. Test results shows that as hardness increases, wear resistance increases.

Carrying out jadeitite diagenesis in its basic state as well as in combination with the multiple fluid activities of water, we focused on jadeite grains in production areas such as Myanmar, Guatemala and Russia to determinethe essence of nominal anhydrous jadeite grains and the distribution of structural hydroxyl in individual jadeite grains via infrared microscope. This is a scientific problem that urgently needs to be solved. The results show that a microscale of structural water in the form of structural hydroxyl is widely found in the jadeite grains of primary jadeitite in Myanmar, Guatemala and Russia. There are certain differences in the three groups of characteristic infrared absorption bands generated by the stretching vibration of the structural hydroxyl in jadeite from these different producing areas. The structural hydroxyl content of the individual jadeite grain shows obvious differences according to the producing areas, and the structural hydroxyl content in jadeite grains in Myanmar is up to 2522.11 × 10 -6 . By contrast, jadeite grains in Guatemala and Russia yield lower results. In addition, the structural hydroxyl content in individual jadeite grains in the three producing areas are inhomogeneous, showing an increasing trend from interior to exterior. However, dynamic metamorphism of different intensities and multi-period fluid participation lead to differences in the increase, whereby an increase in structural hydroxyl content in jadeite grains from Guatemala and Russia is slower. The study of the distribution of structural hydroxyl in jadeite grain from different producing areas is helpful for exploring the interaction trajectory of fluids involved in jadeitite and the diagenesis mechanism of jadeitite, a fact that is of great scientific significance for revealing the formation process and conditions of jadeitite.

Titanium thin films were deposited on glass and indium tin oxide (ITO) coated glass substrates by radio-frequency (RF) magnetron sputtering under varying sputtering parameters as: power, pressure, substrate temperature and target-substrate distance. The crystalline structure, crystallite size and texture coefficients of the films were evaluated in detail. As the evaluation points out, 100 W, 1.33 Pa ambient temperature and 70 mm were determined as the optimum sputtering parameters for intended crystalline structures. Subsequently, electrochemical anodization experiments were performed via varied electrolytes and under various anodization parameters (voltage, time and electrolyte type) in a two-electrode electrochemical cell using the films obtained through the optimized sputtering parameters. The anodized samples were annealed at 450 °C for 1 h in air in order to obtain anatase transformation and the desired crystalline structure. The surface morphologies and the crystalline structures of the anodized films were evaluated through x-ray diffractometer (XRD) and scanning electron microscope (SEM), respectively. Finally, the anodization parameters for the formation of TiO 2 nanotube arrays were determined as: 35 V and 35 min. in an electrolyte composed of 0.3 wt.-% NH 4 F – 2 wt.-% water – ethylene glycol.

The aim of this study is to minimize the decrease in the mechanical properties of materials exposed to environmental conditions by adding nano additives, thereby increasing service life. It has been reported in the literature that boron nitride nanoparticles (BNNP), a multi-walled carbon nanotube (MWCNT), and hybrid (MWCNT + BNNP) nano additives improve the mechanical properties of FRPs and increase their lifetime. For this reason, in this study, filament wound BNNP, MWCNT, and MWCNT + BNNP hybrid reinforced carbon fiber epoxy composite pipes (CFRPs) were produced with (± 55°) 4 configurations and 8 layers. Then, composite pipes were exposed to the hydrothermal aging process in distilled water at 80 °C for 7, 14, and 21 days in order to examine the effects of hot water absorption behavior on mechanical properties such as hardness, and density. The hardness and density measurements were realized in accordance with ASTM standards. The hardness, and density properties of water exposed BNNP, MWCNT, and MWCNT + BNNP hybrid reinforced and non-reinforced CFRPs were examined and compared with unexposed specimens according to ASTM standards. As a result of this study, it was observed that the hardness and density values of the specimens exposed to aging reinforced with nano-sized material were even higher than the hardness and density values of the neat epoxy unexposed to aging. Consequently, although water absorption caused a loss in the mechanical properties of the material, the negative effects of water absorption were minimized thanks to the added nano additives.

This paper presents the findings of comparative research conducted to find out the braking performance of a Mo/NiCrBSi coated automobile brake disc. The friction and wear behavior of the Mo/NiCrBSi coating (CD) used for the disc material was evaluated using a laboratory scale disc-pad dynamometer and compared with a reference disc (RD). The coating was deposited by means of the atmospheric plasma spray process on a grey cast iron substrate. Braking tests were performed according to the SAE-J2430 test standard. Disc microstructures were characterized by SEM and XRD. It was found that the bonding strength was good with an infinite rating between the accumulated coating layer and the substrate. The results show that the coated brake disc has a comparable coefficient of friction and that the amount of wear is lower than that of the reference disc. The addition of ductile phases to the disc coating was beneficial in reducing the coefficient of friction to an acceptable degree and also effectively improving wear resistance.

In this study, two recent algorithms, the whale optimization algorithm and moth-flame optimization, are used to optimize spur gear design. The objective function is the minimization of the total weight of the spur gear pair. Moreover, the optimization problem is subjected to constraints on the main kinematic and geometric conditions as well as to the resistance of the material of the gear system. The comparison between moth-flame optimization (MFO), the whale optimization algorithm (WOA), and previous studies indicate that the final results obtained from both algorithms lead to a reduction in gear weight by 1.05 %. MFO and the WOA are compared with four additional swarm algorithms. The experimental results indicate that the algorithms introduced here, in particular MFO, outperform the four other methods when compared in terms of solution quality, robustness, and high success rate.

Receptacle contacts often are a weak spot of the reliability in electronic systems. During the application phase of the lifecycle, especially in the automotive wiring harness, connectors experience severe loads such as temperature changes. During qualification testing, accelerated tests simulate these thermal stresses. Yet, only the damage mechanisms relevant for service life must be triggered. However, the increasing complexity of electronic components and wiring harnesses demands a continuous adaptation of test strategies. Therefore, this study develops and applies application-oriented load profiles for thermal qualification testing of connectors. Experiments include load profiles inspired by seasonal changes and daily car usage. The tests are carried out on a relative movement test bench as well as in a thermal cycling testing chamber. Contact resistance progression curves, the surface roughness of the contacts, and the area of the stressed contact zones assist in evaluating the effectiveness of the load profiles. All contacts tested during relative movement experiments show no change in contact resistance. The thermal cycling load profile however results in a significant rise in contact resistance. Additionally, the roughness values show varying damages on the contacts due to the different load profiles.

Nano-structured semiconductor thin films and p-type Si photodiodes were fabricated with the sol-gel spin coating technique using pure ZnO and co-doped ZnO:Al x :Cu y with x = 1 at.-%, y = 1, 2, 3, 5 at.-%. The structural and optical properties of thin films were examined using an XRD and a UV-spectrophotometer. The thin films have a hexagonal wurtzite crystal structure, and their optical band gap energies decrease with increasing Cu contribution. The electrical properties of photodiodes were assessed via I-V, C-V, (G/ ω )-V and phototransient current (I-t, C-t) measurements. The Φ b(I-V) , experimental zero-bias barrier height, rectification ratio, ideality factor and I on /I off parameters of the diodes were calculated using thermoionic emission model. In addition, Φ b(C-V) , barrier height, V bi , built-in voltage, V d , diffusion potential, N d , donor concentration and W d , depletion layer width of p-Si/ZnO:Al x :Cu y (x = 1 at.-%, y = 1 at.-%.) photodiodes were obtained using a C -2 -V graph plotted at 1 MHz frequency. The photodiodes exhibit rectifying and photosensitive behaviors, and their reverse bias current increases with increasing light intensity. These results indicate that produced diodes can be employed as photodiodes or photosensors in optoelectronic circuits and electronic devices.

This paper was based on the application of novel breadfruit peel fiber (BFPF), a cheap agro-waste as reinforcer in low-density polyethylene matrix (LDPE) to produce breadfruit peel fiber-low-density-polyethylene composite (BFPF-LDPE) for industrial production. To achieve this, the influence of BFPF weight at different treatment routes on the mechanical properties and water absorption resistance of LDPE was examined. The BFPF was modified with sodium hydroxide (MS), sodium hydroxide/acetic acid (AM) and sodium hydroxide/acetic acid/maleated polyethylene (MM). The results showed that the treatment of BFPF with sodium hydroxide/acetic acid/maleated polyethylene gave better properties than composites produced with either sodium hydroxide or combination of sodium hydroxide/ acetic acid treatment, while untreated (UM) composite provided the poorest. This is a result of anhydride radical in MM which is absent in AM and MS. However, the tensile and impact strength for the crude LDPE indicated higher values than UM, MS, AM and MM of BFPF-LDPE composite, respectively. Furthermore, the tensile modulus, flexural strength and hardness of BFPF-LDPE composite after inclusion of UM, MS, AM and MM showed immense improvement as compared to the raw LDPE. The modified BFPF enhanced sorption resistance of the BFPF-LDPE composite. Therefore, the BFPF-LDPE composite of MM can be applied as an alternative material for the replacement of particle board in construction and automobile parts.

In this research, a novel optimization algorithm, which is a hybrid spotted hyena-Nelder-Mead optimization algorithm (HSHO-NM) algorithm, has been introduced in solving grinding optimization problems. A well-known grinding optimization problem is solved to prove the superiority of the HSHO-NM over other algorithms. The results of the HSHO-NM are compared with others. The results show that HSHO-NM is an efficient optimization approach for obtaining the optimal manufacturing variables in grinding operations.