Volume 23 (2023): Edizione 1 (March 2023)

Plasma welding is characterized by a high concentration of energy, which allows for high welding speed and leads to less distortion and residual stresses compared to conventional welding processes. Due to the local and controlled heat input, the process is suitable for sheet metal from ≈ 0.1 mm (micro plasma) up to ≈ 10 mm. In the case of aluminum and its alloys, the natural aluminum oxide layer on the metal surface limits the productivity of the plasma welding process. The electrically isolating and thermally insulating Al₂O₃ layer has a significantly higher melting point compared to the aluminum (T_m(Al2O3) = 2072 °C vs. T_m(Al) = 660 °C). The oxide layer hinders the formation of a stable arc and can even impede the joining formation. In order to remove the oxide layer and to produce quality welds with a DC process, it is necessary to weld with reverse polarity to use the principle of cathodic surface cleaning. However, this leads to increased electrode wear and increased penetration depth, which is not always desirable.

In the study presented, the use of silane to reduce the oxygen content in the welding atmosphere as well as to remove the natural aluminum oxide layer on the metal surface was investigated. As previous studies have shown that the use of silane-doped plasma-gases is suitable for removing the superficial oxide layer on aluminum components, high-quality welded joints were expected. Quality welds with sufficient dilution were achieved using a transferred arc silane-doped helium plasma. In contrast, welding with an argon-silane mixture led to excessive pores formation. Additionally challenges to stabilize the arc process were identified and ramifications with respect to process optimization are discussed.

Large quantities of waste newspapers and sugarcane bagasse are prevalently discarded by open burning or indiscriminate dumping, thereby posing severe danger to the environment and public health. This study sought to examine the feasibility of managing the wastes by recycling them into value-added products for building construction. Composite panels were fabricated using waste newspaper paste (WNP) with sugarcane bagasse particles (SBP) varied at 0, 25, 50, 75, and 100 % by weight of the composite mix. Epoxy resin was thoroughly mixed with its hardener and applied as binder. The samples were developed in triplicates per proportion of the SBP adopted and then dried completely before their thermophysical and strength properties were evaluated. It was observed that variations in mean values of water absorption (28.57 – 39.43 %), thickness swelling (6.21 - 8.33 %), specific heat capacity (1232 - 1312Jkg⁻¹K⁻¹) trended positively with increasing proportions of the SBP. Whereas nailability remained 100.0 % in all the cases, bulk density (689.4 - 640.5 kgm⁻³), thermal conductivity (0.1186 - 0.1163 Wm⁻¹K⁻¹), thermal diffusivity (1.396 - 1.384 x 10⁻⁷ m²s⁻¹), and flexural strength (2.572 - 2.280 N/mm²) correlated inversely with the added fractions of the SBP. Generally, it was found that the samples could perform satisfactorily if applied as ceiling or partition elements in building design. Therefore, recycling of sugarcane bagasse and waste newspapers as described in this study could serve as a promising way of solving their disposal problems and also enhance achievement of low-cost and safe buildings.

In the present investigation, laminated composite beams subjected to a bending static loading are studied in order to determine their failure mechanisms and the first ply failure (FPF) load. The FPF analysis is performed using a refined rectangular plate element. The present element is formulated based on the classical lamination theory (CLT) to calculate the in-plane stresses. To achieve this goal, several failure criterions, including Tsai-Wu, Tsai-Hill, Hashin, and Maximum Stress criteria, are used to predict failure mechanisms. These criterions are implemented within the finite element code to predict the different failure damages and responses of laminated beams from the initial loading to the final failure. The numerical results obtained using the present element compare favorably with those given by the analytic approaches. It is observed that the numerical results are very close to the analytical results, which demonstrates the accuracy of the present element. Finally, several parameters, such as fiber orientations, stacking sequences, and boundary conditions, are considered to determine and understand their effects on the strength of these laminated beams.

Biopolymer carboxymethyl tamarind seed kernel polysaccharide (CMTSP) was synthesized by the reaction of tamarind kernel powder (TKP) of Tamarindus indica L. with monochloroacetic acid by an improved method. The synthesis was conducted in presence of sodium hydroxide at optimized conditions of time, temperature, concentrations of TKP, MA, sodium hydroxide. Tamarind seed polysaccharide (TSP) was also extracted from TKP by boiling distilled water. The chemical structure of TKP, TSP and CMTSP were analyzed by the ATRFTIR. When TKP, TSP, and CMTSP’s comparative physico-mechanical properties were examined and compared, CMTSP performed better due to increase in viscosity, water solubility and tensile properties.

In this paper study for wave propagation in non-homogeneous porous plate sample with slowly varying refractive index is presented. It is based on simple symmetric solution of the wave equation for linearly polarized electromagnetic wave aligned into the porous plate perpendicularly to the external surface. Using correct boundary conditions both the transverse electric (T.E) and transverse magnetic (T.M) modes, named shortly by (T.E.M) mode for electromagnetic wave, are considered. The Wentzel-Kramers-Brillouin (W.K.B.) solutions for symmetric incident irradiation of fixed power generated at the plate surfaces was obtained. It is done the analysis of the reflection and transmission coefficients on the surfaces of plate.

An effective means for improvement of technical and economic indicators of EAF DC are graphitized cored electrodes, designed at the E.O. Paton Electric Welding Institute. The research works of the first stage, carried out in the industrial furnaces of the type EAF DC-12, showed that the arc of the cored electrode is always maintained in the center of the electrode, a stable electric mode of melting is provided on long arcs and low voltages of the power source. It was established that the voltage in the near cathode area, as well as the range of current and voltage pulsation of the cored electrode arc is significantly lower than in the standard (monolithic) graphitized electrode. These factors determined the saving of active energy, reduction of reactive power losses, increase in cos φ and reduction of the furnace noise level

Stellites are a group of Co-Cr-C-W/Mo-containing alloys showing outstanding behavior under cavitation erosion (CE) operational conditions. The process of ion implantation can improve the CE resistance of metal alloys. This work presents the elaborated original phenomenological model of CE of nitrogen ion implanted HIP-consolidated (Hot Isostatically Pressed) cobalt alloy grade Stellite 6. The ultrasonic vibratory test rig was used for CE testing. The nitrogen ion implantation with 120 keV and fluence of 5 × 10¹⁶ N⁺/cm⁻² improves HIPed Stellite 6 cavitation erosion resistance two times. Ion-implanted HIPed Stellite 6 has more than ten times higher CE resistance than the reference AISI 304 stainless steel sample. Comparative analysis of AFM, SEM and XRD results done at different test intervals reveals the kinetic of CE process. The model includes the surface roughness development and clarifies the meaning of cobalt-based matrix phase transformations under the nitrogen ion implantation and cavitation loads. Ion implantation modifies the cavitation erosion mechanisms of HIPed Stellite 6. The CE of unimplanted alloy starts on material loss initiated at the carbides/matrix interfaces. Deterioration starts with cobalt matrix plastic deformation, weakening the carbides restraint in the metallic matrix. Then, the cobalt-based matrix and further hard carbides are removed. Finally, a deformed cobalt matrix undergoes cracking, accelerating material removal and formation of pits and craters’ growth. The nitrogen ion implantation facilitates ɛ (hcp—hexagonal close-packed)) → γ (fcc—face-centered cubic) phase transformation, which further is reversed due to cavitation loads, i.e., CE induces the γ → ɛ martensitic phase transformation of the cobalt-based matrix. This phenomenon successfully limits carbide removal by consuming the cavitation loads for martensitic transformation at the initial stages of erosion. The CE incubation stage for ion implanted HIPed Stellite 6 lasts longer than for unimplanted due to the higher initial content of γ phase. Moreover, this phase slows the erosion rate by restraining carbides in cobalt-based matrix, facilitating strain-induced martensitic transformation and preventing the surface from severe material loss.