Volume 39 (2021): Issue 2 (June 2021)

This research proposes developing the new hybrid optimization techniques for getting optimized wire EDM machining parameters and analysing the performance and microstructure of hybrid treatment alloy 20 material (high-velocity oxygen fuel spraying and plasma nitriding on iron-nickel-chromium alloy) after machining in wire EDM. The devising optimization is carried out using back-propagation neural networks (BPNN) integrated with fuzzy logic techniques. Taguchi L27 method uses optimized parameters in 3 factors and 3 level methods to BPNN wire EDM processing parameters. Those processing parameter errors are controlled by applying fuzzy logic system in hybrid optimization techniques. The hybrid optimization provides best results (±5% error) while comparing other techniques. This proposal was started with research review of defined factors and BPNN parameters level for hidden layer number, learning algorithm, neurons numbers, and so on. The analysis of variance (ANOVA), analysis of means (ANOM) and signal to noise (S/N) ratio have been used to identify Taguchi results. The BPNN techniques have been employed significantly to tackle hidden layer's uncertain parameter structures. The fuzzy logic controllers in general have been designed engaging the relations between system performance and factor through error method calculation. The microstructure analysis showed that the no evidence was found of recast layer formation on hybrid treated material after machining in wire EDM due to compressive stress and compound layer on material surface.

In this paper, energy band gaps and electrical conductivity based on aluminum selenide (Al₂Se₃) thin films are synthesized electrochemically using cathodic deposition technique, with graphite and carbon as cathode and anode, respectively. Synthesis is done at 353 K from an aqueous solution of analytical grade selenium dioxide (SeO₂), and aluminum chloride (AlCl₂·7H₂O). Junctions-based Al₂Se₃ thin films from a controlled medium of pH 2.0 are deposited on fluorine-doped tin oxide (FTO) substrate using potential voltages varying from 1,000 mV to 1,400 mV and 3 minutes −15 minutes respectively. The films were characterized for optical properties and electrical conductivity using UV-vis and photoelectrochemical cells (PEC) spectroscopy. The PEC reveals a transition in the conduction of the films from p-type to n-type as the potential voltage varies. The energy band gap reduces from 3.2 eV to 2.9 eV with an increase in voltage and 3.3 eV to 2.7 eV with increase in time. These variations indicate successful fabrication of junction-based Al₂Se₃ thin films with noticeable transition in the conductivity type and energy band gap of the materials. Consequently, the fabricated Al₂Se₃ can find useful applications in optoelectronic devices.

The aim of this work involves studying the impact of varied types of steel fibers (SF) on the performance of self-compacting concrete (SCC), containing volcanic pumice powder (VPP). In this study, five types of steel fiber, which had a hooked end with two lengths of (SF1) and (SF3), flat end of length (SF2), in addition to the pointed end of (SF4) and (SF5) by 1% of volume fraction, were used. In addition, hybrid steel fiber (a mixture of all the steel fiber types) by 0.2% of volume fraction of concrete volume was used. Moreover, VPP was utilized by 30% cement mass as a substitute material for producing SCC. The impact of steel fiber properties in the shape of SF on the fresh concrete properties as slump flow and segregation were investigated. In addition to their influence on the compressive strength, split tensile strength, flexural strength, toughness, porosity, water absorption, and bulk density were examined. The results showed that SF led to decreasing the SCC fresh properties. Utilizing SF, on the other hand, improved the SCC hardened properties, as well as the toughness indices.

Both qualitative and quantitative analyses play a key role in the microstructural characterization of nanobainitic steels focused on their mechanical properties. This research demonstrates various methods of microstructure analysis using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) techniques, taking into account these two approaches. The structural constituents have been qualitatively characterized using TEM and selected area electron diffraction (SAED), together with quantitative analysis based on the misorientation angle (EBSD). Besides, quantitative measurement of austenite with both blocky and film-like morphologies has been carried out. Due to the scale of nanostructured bainite, it is also important to control the thickness of bainitic ferrite and film-like austenite; hence, a method for measuring their thickness is presented. Finally, the possibility of measuring the prior-austenite grain size by the EBSD method is also demonstrated and compared with the conventional grain boundary etching method. The presented methods of qualitative and quantitative analyses form a complementary procedure for the microstructural characterization of nanoscale bainitic steels.

The study and application of reversible addition-fragmentation chain transfer (RAFT) polymerization have been widely reported in the literature because of its high compatibility with numerous monomers, reaction conditions, and low polydispersity index. The effect of RAFT agents on the characteristics of the final product is greatly needed to be explored. Our present study aimed to compare the influence of two different types of RAFT agents on the characteristics of the water-soluble polymer (2-acrylamido-2-methylpropane sulfonic acid) (polyAMPS) and their polyAMPS@butyl methacrylate (BMA) core-shell particles. Different analytical techniques including scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were used to ascertain the final morphological, structural, and thermal properties of the resultant products. It was found that RAFT agents have shown a clear influence on the final properties of the resultant polyAMPS and their core-shell particles such as particle size, shape, size distribution, and thermal behavior. This study confirms that RAFT agents can control the final properties of the polymers and their core-shell particles.

Oral dentures are subjected to mechanical and chemical cleansing processes. However, these processes alter the physical and mechanical properties of denture acrylic resins. This study analyzes the surface roughness of conventional heat-cured (HC) polymethacrylate, light-cured (LC) urethane dimethacrylate, and prepolymerized computer-aided design/computer-aided manufacturing (CAD/CAM) dental acrylic resins. The materials were subjected to combined surface treatment of mechanical brushing, thermal cycling, and immersion in chemical disinfectants (corega, chlorhexidine gluconate [CHG], and sodium hypochlorite) to simulate 1 year of clinical use. The surface roughness of the resin specimens before and after surface treatment was evaluated using a noncontact profilometer. Statistical tests based on analysis of variance revealed significant interactions between resin type and disinfectants, indicating that the effects of these two factors were interdependent. The highest and lowest surface roughness was observed in HC resins immersed in CHG and CAD/CAM resins immersed in sodium hypochlorite. Among the materials, HC resins demonstrated the overall highest mean roughness, followed by LC and CAD/CAM resins. Regarding the disinfectant use, the highest mean roughness was observed in disks immersed in CHG, followed by those immersed in corega and sodium hypochlorite. The prepolymerized CAD/CAM acrylic resin demonstrated superior surface quality following combined surface treatments. The HC and LC resins exceeded the roughness threshold and the reported roughness values for acrylic resins following surface treatments. Among the disinfectants tested, sodium hypochlorite produced overall low roughness values.

In this work, the Klein–Nishina (K–N) approach was used to evaluate the electronic, atomic, and energy-transfer cross sections of four elements, namely, zinc (Zn), tellurium (Te), barium (Ba), and bismuth (Bi), for different photon energies (0.662 MeV, 0.835 MeV, 1.170 MeV, 1.330 MeV, and 1.600 MeV). The obtained results were compared with the Monte Carlo method (Geant4 simulation) in terms of mass attenuation and mass energy-transfer coefficients. The results show that the K–N approach and Geant4 simulations are in good agreement for the entire energy range considered. As the photon energy increased from 0.662 MeV to 1.600 MeV, the values of the energy-transfer cross sections decreased from 81.135 cm² to 69.184 cm² in the case of Bi, from 50.832 cm² to 43.344 cm² for Te, from 54.742 cm² to 46.678 cm² for Ba, and from 29.326 cm² to 25.006 cm² for Zn. The obtained results and the detailed information of the attenuation properties for the studied elements would be helpful in developing a new generation of shielding materials against gamma rays.

The study concerns a comprehensive analysis of a multistage hot-die forging on hammers, in order to produce a yoke-type forging, used as a component of excavator power transmission systems. The investigations were conducted with the aim to analyze and identify the sensitive areas in the process and then improve the currently implemented forging technology by using finite element (FE) simulation. QuantorForm (the developer of the QForm program) has developed a thermomechanical numerical model for the production of forked forging. The software Computer-Aided Three-Dimensional Interactive Application (CATIA) was used to develop and build Computer-Aided Design (CAD) models of forging tools. As a result of the numerical simulations, the plastic deformations and temperature distributions for the forgings and tools were obtained, and the force courses during the forging process were analyzed. The obtained results enabled a thorough analysis of the forging process, including identification of potential forging defects (laps) as well as those tool areas that are the most loaded and exposed to damage. On this basis, changes were implemented in the production process, which allowed for the improvement of the currently implemented technology and obtaining the corrected forgings.

Three equivalent exterior precast concrete beam-column (PCBC) connections have been investigated in this study in orderto analyze the effect of steel fiber reinforced concrete (SFRC) as cast-in-place (CIP) on the seismic performance of the PCBC connection. The connection was designed as a ductile connection for a moment-resisting frame and consists of a precast U-beam, precast column with corbel, interlocking bars, and CIP-concrete to connect the precast beam to precast column. The volume fractions of steel fiber incorporated within the CIP-concrete were 0%, 0.5% and 1%. A quasi-static load was applied vertically to the beam tip of the PCBC specimen. The results showed that the steel fibers contained within the CIP-concrete provided 2% increase of the maximum load, 17.7% increase of the energy dissipation, and increase in the joint stiffness of the PCBC connection. The steel fibers delayed the onset of cracking and slowed down the crack propagation, resulting in shorter cracks in the joint core of PCBC specimen, which correlates well with the deflection-hardening characteristic found from the modulus of rupture test.

This work addresses the synthesis of nanocrystalline barium, strontium, and calcium hydroxyapatites (Ca-HAps) via the chemical precipitation method, followed by calcination. To give a coherent picture of the most important structural, textural, and morphological properties of these materials and to investigate the influence of these characteristics over Co²⁺ ion adsorption capacity from aqueous solutions, the powders prepared were systematically characterized by X-ray diffraction, N₂-physisorption measurements, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry, and Fourier Transformed Infrared spectroscopy (FTIR). The results clearly showed that the Ca-HAp obtained exhibits better nanocrystallinity, greater structural stability, high surface area, high total pore volume, and mesoporosity, compared with the other synthesized hydroxyapatites, and that these physicochemical properties share a direct correlation with favorable Co²⁺ ion adsorption capacity at room temperature and pressure. The results proved that the physicochemical features of resulting alkaline-earth hydroxyapatites, prepared via the chemical precipitation method, played a fundamental role during the adsorption of heavy metal (with high toxicity) from aqueous solutions.

This paper is concerned with the analytical solution of a multi-side damage problem. The objective is to investigate the load-bearing capacity of an infinite elastic-plastic plate weakened by three pairs of collinear straight cracks with coalesced yield zones. Stress intensity factors (SIFs) are obtained when yield zones are subjected to three different patterns of yield stress distribution, i. e., constant, linearly, and quadratically varying. Muskhelisvili's complex variable approach is applied for uncovering the solution to this problem. The problem is solved and analyzed rigorously based on Dugdale's hypothesis. The numerical results are deduced for the load-bearing capacity of the plate and yield zone lengths. These results are analyzed and demonstrated graphically for various mechanical loading conditions and different crack lengths.

This paper describes implementation of the finite element method (FEM) to investigate crack growth problems in linear elastic fracture mechanics and the correlation of results with experimental and numerical data. The approach involved using two different software to compute stress intensity factors (SIFs), the crack propagation trajectory, and fatigue life estimation in two and three dimensions. According to the software, crack modeling might be run in various ways. The first is a developed source code program written in the Visual Fortran language, while the second is the widely used ANSYS Mechanical APDL 19.2 software. The fatigue crack propagation trajectory and the corresponding SIFs were predicted using these two software programs. The crack direction was investigated using the maximum circumferential stress theory, and the finite element (FE) analysis for fatigue crack growth was done for both software based on Paris's law. The predicted results in both software demonstrated the influence of holes on the crack growth trajectory and all associated stresses and strains. The study's findings agree with other experimental and numerical crack propagation studies presented in the literature that reveal similar crack propagation trajectory observations.