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Influence of Different Torsion Pitch on Microstructural Evolution and Strengthening Mechanism of Al Wires

Sedighi M., Vaezi A., Pourbashiri M.

Archives of Metallurgy and Materials

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2018

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Vol. 63, iss. 2

625--632

EN

This paper focused on the effect of pure torsion deformation and various torsion pitches on the mechanical properties of the commercial pure Al wires which has not been examined so far. The initial wires with diameter of 4 mm have been torsion deformed to different pitch length (PL). In order to investigate the effect of gradient microstructure caused by torsion deformation, three different pitch length of 15 mm, 20 mm and 30 mm are considered. The results revealed that the level of grain refinement is correlated with the amount of induced plastic shear strain by torsion deformation. For the wire with pitch length of 15 mm, the grain sizes decreased to about 106 μm and 47 μm in the wire center and edge from the initial size of about 150 μm of the annealed wire. The micro-hardness measurement results show a gradient distribution of hardness from the wire center to the wire surface that confirmed the increasing trend of plastic shear strain obtained by FE simulations. The hardness of annealed sample (35 HV) is increased up to 73 HV at the wire surface for the smallest pitch length. The yield and ultimate tensile strength of the torsion deformed wires are also increased up to about 85 MPa and 152 MPa from the initial values of 38 MPa and 103 MPa of the annealed one respectively while the maximum elongation reduced significantly.

2

Role of filling material on defects of thin-walled tube bending process

Sedighi M., Kahnamouei J. T.

Journal of Theoretical and Applied Mechanics

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2014

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Vol. 52 nr 1

227--233

EN

This paper investigates approaches to avoid common defects such as the wrinkling, cross section distortion and changing in wall thickness in the bending process of a thin-walled tube. A series of experimental tests has been carried out by filling the tube with melted lead and different types of rubbers. Firstly, tubes were filled by several kinds of rubbers and bended, but the wrinkling was observed at the inner side of the tubes. Also the cross section distortions happened to be above the acceptable range. Therefore, rubbers could not be a suitable filling material for steel tubes. As the second case, lead was used as the filling material to avoid the defects. For this purpose, the tubes were filled by liquid lead and it was solidified to form a leady core to support the inner part of the tube bend. After the bending process, lead is melted and removed. This removable leady core was called the ‘Leady Lost Core’. To study the process numerically, a 3D finite element model of the horizontal bending process has been built using a commercial code. Experimental tests have been carried out to verify the simulation results and developed to provide additional insight. To consider the friction coefficient, in this work, “The Barrel Compression Test” method has been used. Comparisons between the experimental and finite element results have shown remarkable agreement. They show that wrinkle initiation and cross section distortion can be avoided with a lost core of low temperature melting metal like lead or tin.

3

Experimental study on ultimate strength of CK20 steel cylindrical panels subjected to compressive axial load

Shariati M., Sedighi M., Saemi J., Eipakchi H. R., Allahbakhsh H. R.

Archives of Civil and Mechanical Engineering

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2010

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Vol. 10, no 2

117-130

EN

In this paper, the effects of the length, sector angle and boundary conditions on the buckling load and postbuckling behaviour of cylindrical panels have been studied, experimentally. The compressive axial load has been applied on the panels using servo-hydraulic machine and different boundary conditions have been prepared by suitable fixtures. The presented results can be used in designing of these structures.

PL

W pracy przedstawiono eksperymentalne wyniki wpływu długości i kąta sektora próbek oraz warunków brzegowych na siłę wyboczenia oraz ich zachowanie się po wyboczeniu. Badania przeprowadzono na maszynie hydraulicznej, gdzie za pomocą odpowiednich uchwytów uzyskano różne warunki brzegowe. Przedstawione wyniki mogą być wykorzystane w projektowaniu struktur cylindrycznych.

4

Comparison of different gravity field implied density models of the topography

Sedighi M., Tabatabaee S., Najafi-Alamdari M.

Acta Geophysica

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2009

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Vol. 57, no. 2

257-270

EN

Density within the Earth crust varies between 1.0 and 3.0 g/cm³. The Bouguer gravity field measured in south Iran is analyzed using four different regional-residual separation techniques to obtain a residual map of the gravity field suitable for density modeling of topography. A density model of topography with radial and lateral distribution of density is required for an accurate determination of the geoid, e.g., in the Stokes-Helmert approach. The apparent density mapping technique is used to convert the four residual Bouguer anomaly fields into the corresponding four gravity im-plied subsurface density (GRADEN) models. Although all four density models showed good correlation with the geological density (GEODEN) model of the region, the GRADEN models obtained by high-pass filter-ing and GGM high-pass filtering show better numerical correlation with GEODEN model than the other models.