Advanced Materials Research Vol. 1158

Abstract: Source-based method for modelling solidification problems have been modified and presented in the current work. It coupled the effect of thermal radiation to macro-transport codes and was solved using finite volume method. The problem was formulated based on the classic continuum energy conservation equation for transient conduction controlled solidification system. Radiation heat transfer and latent heat evolution were added as source terms and solved with appropriate numerical treatments to obtain a system of linearized source terms. This circumvented the need for the application of any analytical solution to the intricate heat transfer regimes included in the model. The effect of cooling was carried out under various cooling conditions imposed on different surfaces of the mould for the solidifying metal. The resultant influence of cooling on the solid fraction evolution during static casting was then evaluated. The simulated cooling curves show that thermal radiation have no influence on the rate of heat extraction and the results show that the predicted cooling curves and solid fraction updates are similar to the results of previous models. The predicted curves at the top section of the open mould however show a little deviation due to effect of surface tension gradient forces. It was further revealed that heat transfer coefficients has more effect cooling curves and temperature contours at the lateral mould surfaces than the interior of the casting which is in agreement with theory of Newtonian cooling.

Abstract: TiNbSn alloys have been extensively researched due to several properties they exhibit, including high mechanical strength, low elastic modulus, superelasticity, shape memory effect, biocompatibility. The present study evaluated the cryogenic heat treatment in the Ti35NbxSn alloys (x = 0.0; 2.5; 5.0; 7.5). The alloys were arc melted, cold formed and quenched in both water and liquid nitrogen at-198° C. The Ti35Nb2.5Sn alloy was also aged after exposed to both quenching medium. Microstructure and microhardness analyses were performed. Cryogenic treatment was not enough for transformation of primary β phase into martensitic α” in alloys containing 5 and 7.5% Sn. Cryogenic treatment provided β to α” transformation in alloys containing 0 and 2.5% Sn. The Sn-free alloy was more likely to α" transformation in both quenching medium. The alloys microhardness increased with decrease of both quenching temperature and Sn content. The increase of α" is also related to the increase of the alloy microhardness after aging.

Abstract: Pipelines for oil and gas, manufactured in high-strength low-alloy steels (HSLA), such API pipes, promote high levels of strength and fracture toughness. Therefore, it is important to ensure this high level of toughness in the welded joint. When the pipelines are exposed for many years to wet H₂S environments, they can fail due to hydrogen embrittlement. Thus, it is important to evaluate the influence of different weld specifications in the susceptibility to hydrogen embrittlement. In this case, the aim of this work was to study the susceptibility to hydrogen embrittlement of API 5L X52 steel and in the welded region in wet environments. The welding was performed in the circumferential direction by GMAW process in two different specifications (with lower and higher thermal input). The susceptibility to hydrogen embrittlement was carried out according to NACE TM0177 and SSRT (slow strain rate tensile tests) test, performed according to ASTM G 129 standard. All welded joints and base metal did not show any signal of cracks and susceptibility to hydrogen embrittlement, according to the requirements of the NACE TM0177 test. According to SSRT tensile test, the results showed that the welded joints and base metal are susceptible to hydrogen embrittlement. The tensile tests exhibited a drop in the strain and necking, and higher values of yield stress. The welded joint with the lowest heat inputs employed in the welding process presented the highest susceptibility to hydrogen embrittlement.

Abstract: Bulk metallic glass matrix composites have emerged as new potential material for structural engineering applications owing to their superior strength, hardness and high elastic strain limit. However, their behaviour is dubious. They manifest brittleness and inferior ductility which limit their applications. Various methods have been proposed to overcome this problem. Out of these, introduction of foreign particles (inoculants) during solidification have been proposed as most effective. In this study, an effort has been made to delimit this drawback. A systematic tale has been presented which explain the evolution of microstructure in Zr_47.5Cu_45.5Al₅Co₂ and Zr₆₅Cu₁₅Al₁₀Ni₁₀ bulk metallic glass matrix composites with varying percentage of ZrC inoculant as analysed by secondary electron and back scatter electron imaging of as cast unetched samples. A support is provided to hypothesis that inoculation remain successful in promoting phase formation and crystallinity and improve toughness.

Abstract: In this study, the tensile and flexural strengths of cottonseed hull reinforced epoxy composites were investigated. Specimens were made using a stainless steel mold. A hand lay-up process was used to make the composite material, and three kinds of materials were made: unreinforced epoxy, raw cottonseed hull reinforced composite, and grinded cottonseed hull reinforced composite. The fiber content of all composites is 15 wt%. Tensile and flexural test were performed with universal testing machine. The result shown that Tensile and flexural strengths of grinded cottonseed hull reinforced composites were found to be the highest.

Abstract: In the present paper (1-x)Pb (Zr_1-yTi_y)O₃ – xPb (Mn_1/3Sb_2/3)O₃ – z at%E system, with E = Pr³⁺, Nd⁵⁺ and Gd³⁺ where x = 0.12; y = 0.48; z = 0 and 0.02 ceramic synthesized by solid state reaction technique is analysed. The investigation aims studying of the effect of dopants on the dielectric and piezoelectric properties of such piezoelectric ceramic. The prepared powders have been uniaxially pressed into discs with diameter of 10 – 12 mm and thickness of 1.2 mm. Sintering has been carried out in air atmosphere at temperatures of 1150^°C and 1200^°C, respectively, for 2 hours each, followed by a controlled cooling at a rate of 200^°C /h. The piezoelectric properties have been investigated after a suitable preparation, including polishing, metallization. The structure of the samples has been determined by X-ray diffractometry (XRD), while the morphology and grains size have been investigated by the scanning electron microscopy (SEM). The piezoelectric properties have been studied by the resonance - antiresonance method. XRD analysis reveals a perovskite tetragonal structure and, as expected for ceramic materials, SEM analysis indicates that the average grain size increases as sintering temperature increases. The dielectric and piezoelectric properties have been determined measuring the ceramic discs, and properties, as dielectric permittivity (ε_r), dielectric loss (tg δ), and the electromechanical coupling factor (k_p) have been obtained. The acquired results indicate a significant effect of the dopants on the dielectric and piezoelectric properties of such materials.

Abstract: This paper emphases on the effect of various machining constraint on surface roughness and material removal rate in turning SiC reinforced Al alloy composite through taguchi orthogonal array based experimental analysis which has been further optimized using principal component analysis (PCA). Experimental investigation has been conducted under minimum quality lubricant (MQL) cutting environment. Palm oil has been used as lubricant where flow rate and pressure were kept at 120 ml/hr and 8 bar. The whole experiment has been designed using L₂₅ orthogonal array having three input parameters and five different level to measure surface roughness and material removal rate. Taguchi S/N ratio-based optimization has been implemented where smaller the better criteria has been used for surface roughness whereas larger the better criteria has been used for material removal rate. From Analysis of variance, it is observed that cutting speed and feed rate are the most prominent factor for surface roughness. Nevertheless, Depth of cut and cutting speed are the most dominant factor for material removal rate. While comparing the predicted output values with experimental values, MAPE value is found in the range of 0.23 % for surface roughness and 0.045 % for material removal rate which is in very much tolerable range. Correlation coefficient value for experimental values of the resultant output is 0.98286 and 0.99869 respectively which signifies the effectiveness of the whole experiment. Subsequently, machining parameters were optimized using PCA technique. To attain satisfactory response values, depth of cut, cutting speed and feed rate need to be at 0.85 mm, 396 m/min and 0.16 mm/rev respectively. By applying the model, surface roughness of 0.7257 μm and MRR of 53856 mm³/min can be obtained. Keywords: SiC reinforced Al alloy; Turing; Minimum Quality Lubricant; Surface Roughness; MRR; Taguchi orthogonal array; Principal component analysis

Abstract: In a quest for a cleaner planet and to have alternative forms of energy generation apart from the fossil-based power supply, fuel cell technology has emerged as an alternative energy source for usage across all economic sectors. The application of this age-old technology is found in alkaline (AFC), molten carbonate (MCFC), phosphoric acid (PAFC), polymer electrolyte membrane (PEMFC) and solid oxide (SOFC) fuel cells. These fuel cells are named based on the type of electrolyte employed in their applications and the fuel of choice for energy generation is hydrogen. This fuel can be used in its pure form or extracted from other sources such as methanol, water and syngas. Ammonia in its liquefied and gaseous forms may be used as a non-carbonaceous fuel for the hydrogen source in some of these fuel cell technologies due to its safety, lower price, ease of storage and transportation. In this review, all the fuel cells will be investigated in their capability of using ammonia as a direct fuel. The role of earth abundant metal catalysts in comparison to TiO₂ was evaluated in terms of molecular orbital theory and in the decomposition of organic compounds and other material into nitrogen and hydrogen products under the visible light radiation. The p-orbital participation in earth abundant metals or metal oxides doping, emerged as a strong contribution to bandgap attenuation.

Abstract: The impact-echo method is commonly used for detection of flaws in concrete elements based on the shift in the thickness frequency of a plate-like member. However, there is a need to develop this efficient technique for other applications. This paper investigates the feasibility of using the impact echo-method for identifying corrosion of steel reinforcement in concrete structures. For this purpose, 180 reinforced concrete cubes were cast and tested. The main parameters studied were the amount of recycled aggregate (i.e. 0%, 25%, 50% and 100%), nanosilica (1.5% and 3%) and the steel bar diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. The impact-echo results were correlated against the actual corrosion levels obtained by the mass loss method. The experimental results showed that the response of impact echo in terms of frequency peaks is found to be sensitive to the high and moderate levels of corrosion. However, no clear trend was observed at the initial stage of corrosion. It is demonstrated that the impact-echo testing can be effectively used to qualitatively detect the damage caused by corrosion phenomenon in reinforced concrete structures.

Abstract: The main motivation in stamping die industry and academia is panel quality and formability issues rather than the weight and cost of the die. A product should be designed according to the loads that it can be faced in service condition. But somehow this rule is not valid for stamping die design since the minimum distance between the ribs is based on the standards and location and pattern of the ribs which are depending primarily on the company experience. In this work, an auto panel drawing die design is investigated numerically whether it is overdesigned or not. The loads on the die surfaces are calculated by numerical methods. When a panel is drawn between upper and lower die, the contact pressure (CP) occurs on the interface surfaces due to this interaction. Since CP is a vital parameter and it is almost impossible to measure it by experimental methods, it is validated by two different numerical codes. The CP values obtained from Autoform^® quasi-static solution are compared with Abaqus^® transient forming analysis solution. Topology optimization is applied on the lower die by using the estimated CP loads. Von-Mises stress, elastic deformation and volume are compared between current and optimized die geometry. Panel thickness variation is also investigated in longitudinal and transverse directions.