Volume 62, Issue 8

This study proposes a method for integrating finite element analysis and response surface methodology to predict tearing locations in the deep drawing of a rectangular-shape AISI 304 cup. The finite element model was confirmed by a deep-drawing experiment with nitrogengas springs, and the finite element analysis results were in agreement. Moreover, the regression model was developed using response surface methodology to predict final thickness at various locations on the rectangular-shape deep-drawn cup based on 40 finite element cases containing varied blank holder forces. The maximum percentage of thinning values was obtained from the response surface methodology results. The relationships among the blank holder forces and the thinning values at different locations were then further developed. The maps of the predicted tearing locations were then obtained and directly corresponded to the number of locations the specific blank holder forces. These maps, as established, could be directly used in a closed-loop control system enabling tearing defects to be prevented or eliminated.

Metallic dental implants such as titanium and stainless steel have an elastic modulus 5-14 times greater than that of compact bone (15 GPa). These stiff implants do not adequately strain the bone, which can result in bone resorption through a phenomenon referred to as stress shielding. The implant length and diameter has a significant influence on the stress distribution within the surrounding jawbone. Therefore, the objective of this investigation is to optimize the material and the dimensions of a dental implant. A numerical solution of a 3D finite element analysis using ANSYS software was conducted to achieve this purpose. It was concluded that by using stainless steel, titanium or gold dental implants with a large diameter and short length the values of the maximum von Mises stress values in cortical bone were increased. The maximum increase in von Mises stress can be obtained by using a stainless steel implant. This dental implant will reduce the stress shielding effect as well as yield suitable values with respect to von Mises stress for both porcelain crowns and dental implants, thus increasing the service life of the implant.

In the research reported in this contribution, chromium-zirconium nitride (CrZrN) layers were deposited on (100) silicon wafer by balance magnetron sputtering using argon and nitrogen as working and reactive gas, respectively. The coating layers were categorized into three groups according to zirconium content; low-zirconium (Low-Zr), medium-zirconium (Med-Zr) and high-zirconium (High-Zr). All layers had thicknesses in the range of 1.0-1.3 μm and the Med-Zr was the thickest sample. From the X-ray diffraction (XRD) results, zirconium could partially dissolve in chromium nitride (CrN) and formed complex nitride of chromium-zirconium [(Cr,Zr)N]. This phasic group was dominant for all samples, and the average crystallite sizes decreased with increasing zirconium fraction. In addition, the High-Zr sample had an extra broadened peak among (Cr,Zr)N peaks which could not clearly be identified by XRD. This ambiguity was eliminated by X-ray photoelectron spectroscopy (XPS). It was determined to be amorphous of zirconium oxynitride (Zr2ON2). Because of the high oxygen sensitivity of zirconium, it reacted with nitrogen and residual oxygen forming Zr2ON2. This study is among the first to examine the resulting nanoscale structure of the CrN layers incorporated with a high amount of zirconium.

White cast iron with about 12.7 wt.-% chromium was alloyed with Ni, W and Mo for heat treatment applications. Heat treatments were performed at a range of 850-1050 °C for 1 h in order to distribute M7C3 carbides homogeneously in an environment of high wear resistance. The contents of the C, Cr, Ni, Mo, Mn and Si elements selected for the alloys were similar, though a 6 wt.-% nickel concentration was chosen. Microstructural changes in the specimens were examined by scanning electron microscopy (SEM) and optical microscopy (OM). Macro-hardness, average carbide size and volume fraction were analyzed. Wear tests were carried out under different loads of 10, 20 and 30 N. It was seen that heat treatment changed the carbide size and homogeneous distribution of the carbides. Moreover, the addition of nickel to HCrWCI increased fracture toughness and reduced the wear rate.

In the present study, AA 2024-T351 plates with a thickness of 6 mm were joined using the friction stir welding technique with three different tool rotational speeds and two different pin profiles. Microstructural features and mechanical properties of welded joints were investigated. The grains in recrystallized regions along the stir zone were observed to be almost with invariable sizes. The grain size was revealed to increase with the increase in tool rotational speed. The average grain size was observed to dramatically increase from 2.3 μm to 5.6 μm for welded joints produced with pentagonal shaped pin. All the welded joints were observed to contain defects; the presence of defects exhibited a negative effect on the tensile properties of the welded joint. Most of the defects were observed to localize at the root region of joints. The joint, welded with the tool rotational speed of 250 rpm using pentagonal shaped pin, exhibited ultimate tensile strength with a value of 365 MPa. The ultimate tensile strength of welded joints was found to be higher with the decrease in the tool rotational speed. The welding efficiency of joints was compared with the ultimate tensile strength of base metal; notably, welding efficiency values between 46 % and 80 % were achieved. Microstructural characterizations revealed that Al2Cu (θ phase), Al2CuMg (S phase), and AlCuFeMnSi, Al7Cu2Fe intermetallic particles were dispersed in the stir zone.

Applied mechanical stress could accelerate the chemical or electrochemical process of metal corrosion in weak acid solution. Series of experimental tests were conducted in this research. The results show that there is no obvious correlation between OCP (open circuit potential) values and applied stresses. However, The LPR (linear polarization resistance)corrosion rate increased intensively under the applied stress of 400 MPa. Correspondingly, the EIS (electrochemical impedance spectroscopy) Nyquist diagrams show that all of the plots contain a semicircle over the whole frequency range and the semicircle size decreased with increasing applied stress. The real-time corrosion current square waves triggered by the mechanical stress were successfully monitored by using the potentiostatic method in CO2 saturated brine under 200 mv (above OCP), flow and lower pH condition. This result is significant for many research fields, such as petrochemistry, aerospace and nuclear industries, which suffer weak acid corrosive environment.

In this paper, the removal of the sulfide layer formed on an FV(520)B stainless steel in the simulated environment of air compressor blade service conditions in a reaction kettle by arc plasma was investigated to explore the mechanism and technology of the sulfide layer removed by arc plasma from a blade surface. The sulfide lattice energy is studied by using the Born Haber cycle. Besides, the energy balance of the removal process is calculated. The treated surface morphology of samples was analyzed by scanning electron microscopy and energy dispersive spectrometer. The results indicate that the energy of the arc spot is enough to evaporate the sulfide film. Due to the different electronic work functions, an arc spot is first formed on the sulfide film, and then the voltage signal is segmented during the removal process. The voltage signal in the removal process can remove sulfide without harming the metal matrix. Besides, the increase in current can improve the removal efficiency and the surface roughness of the sample. It can be revealed, by analyzing the surface composition of samples with different currents, that the sulfur content is very low, indicating that it is feasible to remove the sulfide layer by arc spot plasma.

The application of anatase titanium dioxide (TiO 2 ), which is an abundant and cost effective resource, in supercapacitors has been restricted due to its poor electronic conductivity and limited mechanical stability. A biomass-derived carbon was coated on anatase TiO 2 nanoparticles via practical and green hydrothermal carbonization in order to overcome these limitations. Hierarchically porous carbon provided a capacitive double layer for charge storage and the TiO 2 /C nanocomposite exhibited a specific capacitance of 61 F × g -1 (0.25 A × g -1 , 0 to 1 V vs. Ag/AgCl, 1 M H 2 SO 4 aqueous electrolyte). The TiO 2 /C/PEDOT:PSS nanocomposite with enhanced specific capacitance and rate capability (189 F × g -1 at 0.25 A × g -1 , 161 F × g -1 at 0.5 A × g -1 , 123 F × g-1 at 1 A × g -1 , 91 F × g -1 at 2 A × g -1 ) was obtained by the application of an electrochemically active PEDOT:PSS layer. The prominent electrochemical and mechanical stability of the ternary nanocomposite was demonstrated by its ability to retain 98 % of its initial capacitance after 1500 cycles of charge-discharge at a high current rate (3 A × g -1 ). The synergistic use of sustainable organic and inorganic components with environmentally friendly and practical methods yields extremely promising electrochemical performances for supercapacitor applications. The TiO 2 /C/PEDOT:PSS nanocomposite presented in this work delivered an electrochemical performance comparable to its published counterparts which are obtained by more sophisticated or hazardous methods and with expensive components.

The laser cutting method of the conventionally used material nodular cast iron, including the technological parameters influencing its cutting edge quality, is described in this paper. Samples were created by using different laser cutting technological parameters. The parameters, varied during the experiments, included the type of assist gases (O 2 and N 2 /O 2 combination - with different ratios of the two gases) and the cutting speed (within a range of 1.6 mm/min to 0.32 mm/min). Both parameters were changed until the desired properties of the cut surface were obtained. The heat affected zone’s width, microstructure and roughness parameters, were monitored for samples of thickness t = 13 mm. Results of the heat affected zone width measurements and its microstructure are shown in figures and evaluated for comparison purposes. The laser cutting principles and technology are briefly described, as well (properties of the CO 2 laser beam, laser cutting input parameters, assist gases, interaction with the target material and stability of the cutting process).

Vibration amplitudes in machining operations have a deteriorating influence on the outcomes of the processes. Moreover, eradicating them is an impossible task due to the natural mechanism of cutting metals. However, by selecting the optimum cutting parameters, the destructive effects of vibration amplitudes may be diminished to acceptable levels. In the present paper, AISI 1050 steel material was machined, employing carbide inserts and a CNC lathe machine. Cutting tool approaching angles were selected between -5° and 45°, feed rates from 0.1 mm × rev -1 to 0.5 mm × rev-1, cutting depths between 0.5 mm and 2.25 mm, and accordingly CSR values between 1 and 15. The effect of the selected parameters on the chip compression factor (CCF), shearing length feed (SLF), shearing length (SLA), surface roughness, and chip morphology was investigated. Moreover, the effect of CCF, SLF, and SLA on surface roughness, vibration amplitudes, and chip morphology was analyzed as well. It was found that the most influential parameter on shearing length was cutting depth while the feed rate was on the surface roughness. The optimum CCF values were between 1.7 and 2.3, SLF smaller than 1, and SLA around 5. Furthermore, it was shown that the optimum CSR values were 10 and 15, and cutting tool approaching angles 30° and 45°, according to the chip morphology criterion.

Design freedom, complex geometry fabrication capability, minimal parts assembly and excellent material utilization attributes of additive manufacturing processes have provided a leverage ground for the development of functional engineering steel parts in the manufacturing industries. Despite the good attributes of additive manufacturing technology, there are still some local and inherent defects of as-built steel parts that can jeopardize the overall integrity of structural steel components. This review paper provides the associated defects of as-built steel and summarizes the post-manufacturing strategies being deployed to mitigate the severity of as-built steel defects. The microstructural and mechanical responses of some specific as-built steel under different fabrication conditions or additive manufacturing techniques are also summarized in this paper.

The main reason for vibration and tool deflection in boring processes are the geometrical, mechanical, and physical properties of the boring bar employed. The diameter of the boring bar is rather small when compared with its length due to the nature of the mechanism in the boring process., In the present study, the influence of the physical properties of boring bars on the deflection amplitudes, natural, and circular natural frequencies were investigated both theoretically and experimentally. For that purpose, seven kinds of boring bars were used. The influence of the characters of boring bars on the amplitudes of tool deflection was investigated both theoretically and experimentally. By contrast, this influence on the natural and the circular natural frequencies were investigated only theoretically. It was found that boring bars filled with rubber and silicon recorded the smallest deflection amplitudes. Particularly, bars filled with silicon manifested the lower tool deflection amplitudes under the selected conditions. It should be added that lower feed rates and cutting depths caused severe tool deflection amplitudes. Moreover, the optimum compatibility between the theoretical and experimental results of tool deflection amplitudes was observed in bars filled with silicon ∅ 16 mm.

Natural rubber composites are widely used in the automotive industry because of their improved viscoelastic characteristics that are mostly governed by crosslink density. However, rubber parts suffer deterioration of performance over long service lives. Therefore, optimization of crosslink density and prediction of changes in physico-mechanical properties over time at elevated temperatures is extremely important for the production of safe auto parts. In this work, the effect of vulcanization time on crosslink density and thus the performance and lifetime of natural rubberbased auto parts was investigated. The natural rubber mixture prepared in this context was vulcanized for 3, 5, 10 and 15 minutes at a constant temperature of 160 °C. The crosslink density of each vulcanizite was determined by equilibrium swelling tests and the Flory-Rehner equation. The maximum crosslink density (10.75 × 10 -5 mol × cm -3 ) and the minimum permanent compression set values (10 % at 70 °C and 25 % at 100 °C) were recorded for the sample vulcanized for 10 minutes (v10). Aging behavior of the samples were investigated by stress relaxation tests performed at 85 °C, 100 °C and 120 °C. The service lives of the vulcanizites at different temperatures were predicted by linear Arrhenius fits of degradation times. The sample vulcanized for 10 minutes (v10) was shown to exhibit a service life of 2282 hours at 70 °C in air and the optimum physico-mechanical performance under real operating conditions. The performance and lifetime prediction procedure used in this work could be employed in an early design of rubber components for specific applications.

In this study, the effect of current on the tensile and microstructural characteristics of magnetic arc oscillation welded AZ31B magnesium alloy joints has been investigated. Five joints were constructed using different levels of current (65 A - 85 A). It was found that the joints constructed using a current of 75 A yielded superior tensile properties as compared to the other joints. The formation of finer grains and higher hardness in fusion zone and uniformly distributed precipitates are the main reasons for the superior tensile properties of these joints.