Authors: Jovica. Ilić, Tatjana Grbić, Miodrag Hadžistević, Mladomir Milutinović, Milija Kraišnik, Dejan Movrin

Abstract

The analysis of influencing factors and their effects on the deep drawing process is essential for producing cost-effective, high-quality workpieces. In this study, the impact of deep drawing process variables, including die radius, blank holder force, and lubrication conditions, on the distribution of wall thickness and changes in radius for axisymmetric workpieces is explored. For the investigation, specialized tooling was created, with core components such as the punch, die, and blank holder made from a two-component resin and fabricated using rapid tooling technology - vacuum casting. The Taguchi method was employed as a statistical tool for planning the experiments, which allowed the impact of process factors to be determined with minimal variability.

Key words: deep drawing, rapid tooling, Taguchi method,

DOI: 10.24867/ATM-2023-1-005

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Authors: Srđan Bulatović, Vujadin Aleksić, Bojana Zečević, Biljana Prohaska

Abstract

Designing, constructing and putting into operation a hydroelectric power plant includes complex tasks. Stresses of turbine and hydromechanical equipment of hydro power plants arise during the production of parts and assembly of equipment (residual stresses), in the process of performing functional requirements in exploitation and in the disturbed process of exploitation. After several decades of constant exploitation of the horizontal bulb turbine, which is an integral part of the hydroelectric power unit, empirically, the formation of a crack occurs in the turbine shaft due to the influence of corrosion, erosion and cavitation. Through experimental tests and calculations it has been determined that values of bending stresses of the turbine, which occur due to the action of fatigue and corrosion, as well as stress concentration, are bigger than 25 MPa for flanges exposed to water, and in other case bigger than 40 MPa for flanges exposed to `corrosive water` and can cause the occurrence of surface cracks on the transition radius between the cylindrical part of the shaft and the flange. It has been determined that stress values in the zone under the influence of bending stresses were bigger than allowable values, which led to the occurrence of many cracks due to fatigue corrosion. One of those cracks caused the failure of the shaft and of the whole turbine.

Key words: crack, turbine shaft, fatigue, stress concentration

DOI: 10.24867/ATM-2023-1-004

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Authors: Srbislav Aleksandrović, Djordje Ivković, Dušan Arsić, Marko Delić, Slaviša Djačić, Milan Djordjević

Abstract

The aim of this paper is to show influence of two elements on plastic strain ratio value, or "r" value. The first element is value of plastic strain, and second is specimen geometry. Extensive experiment was conducted according to appropriate tensile test procedure with 3 materials and 5 different specimen geometries. Steel sheet S235JR, austenitic stainless-steel sheet X5CrNi18-10 and Al alloy sheet AlSi0.9MgMn (i.e. ENAW 6081) were used during the experiments. Nominal thickness for all three sheets was 1 mm. Three out of five specimen geometries had 20 mm width and gage length of 60, 120 and 160 mm while the rest of specimens had width of 15 mm and gage length of 50, 100 mm. All the specimens were laser cut in rolling direction. In preparation part of the experiment, behind material characterization (obtaining base mechanical properties) identification of homogenous deformation field was performed, i.e. plastic strain at the beginning of localization, for each specimen. Related to that strain value 6 degrees of deformation were realized: 75%, 80%, 85%, 90%, 95% and 100%. Results showed expected and significant difference in "r" value for used materials, but influence of specimen geometry and realized plastic strains were low.

Key words: sheet metal, anisotropy, plastic strain ratio, S2235JR, X5CrNi18-10, AlSi0.9MgMn;

DOI: 10.24867/ATM-2023-1-003

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Authors: Darko Šunjić, Stipo Buljan

Abstract

Explosive forming is one of the non-conventional impulse technologies of metal forming technologies and it is a relatively young technology that has not been fully explored. The origin, development and application of explosive forming technology is given in this paper, and the advantages and disadvantages are also described. Given the specificity of this technology, this paper presents the calculation of the mass of the explosive as the most important factor in this process and the calculation of the pressure of the shock wave. In fact, with conventional deep drawing technologies, it is possible to design the technology and follow the same steps to reach products of different dimensions. In explosive forming, this is a problem, and it is not possible to follow these rules. Experiments of explosive forming can only be performed by employees trained to work with explosives, following prescribed procedures.

Key words: explosive forming; mass of explosive; velocity speed; pressure

DOI: 10.24867/ATM-2023-1-002

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Authors: Talabi Henry K

Abstract

The mechanical behaviour of Al6063 alloy matrix composites reinforced with rice husk ash (RHA), silicon carbide (SiC) and copper nanoparticles (CuNP) has been investigated. Rice husk ash and silicon carbide mixed in fixed weight ratios of 3: 1 while copper nanoparticles were varied from 1 to 4 weight ratio to prepare hybrid reinforced Al6063 based composites using two-step stir casting and spin casting technique. Hardness measurement, tensile testing, impact toughness, optical and scanning electron microscopy were used to characterize the composites produced. It was observed that as the density increases with the increase in addition of copper nanoparticles, the porosity reduces. It was also observed that hardness increases with increase in copper nanoparticles addition. The ultimate tensile strength and impact toughness increased with increase in copper nanoparticles. The impact toughness of reinforced composites improved with increase in copper nanoparticles addition. The composition with 4 wt. % copper nanoparticles exhibited superior combination of properties that may be useful for design of components for automobile application.

Key words: aluminium matrix composite; rice husk ash; silicon carbide; copper nanoparticles

DOI: 10.24867/ATM-2023-1-001

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