Wyniki 1-4 spośród 4 dla zapytania: authorDesc:"Maroš MARTINKOVIČ"

Analysis of material flow in semisolid state during backward extrusion DOI:10.15199/24.2019.8.7


  Introduction. Semi-solid metal processing became possible about 25 years ago [1]. It has been found that by rheological processing of the metal during solidification, a semisolidified slurry is formed which is able to hold the shape such that it can also be manipulated by a robotic device [3]. However, the partially solidified samples were liquid when formed during controlled cooling of the molten metal. Later analyzes of the microstructure showed why. The slow cooling and application of intense flow produces solid phase particles that are large and spherical in shape. While rapid solidification and short flow of material produce small, rugged particles that tend to stick and agglomerate with each other [2]. As a result, the larger particles slope more easily than the smaller ones, which are more advantageous for the production of semi-solid compositions with greater creep resistance [6]. Using of backward extrusion, a cup shape forming part can be produced. The flow of material in the wall and bottom is well mathematically described, but in the corner of the body the material flow is not mathematically described [5]. Using the methods of quantitative metallography [4], the flow of material of eutectic SiAl alloy (silumin) in semisolid state in this area can be determined. In a metallographic cut secondary dendritic arm spacings (SDAS) can be used for estimation of the material flow. Faster flow of the material lea[...]

Modelling of Plastic Deformation in Polycrystalline Material DOI:10.15199/24.2017.8.21


  Introduction. Mechanical working leads to final proper􀀐 ties of forming pieces, which are affected by conditions of production technology. Recently the forming is in generally way based on macroscopic effects of deformation, but the􀀐 se are not corresponding fully with microscopic structural changes. The macroscopic strain does not reflect micro􀀐 structural changes in volume of deformed parts of mate􀀐 rial mainly in case if only surface layers are deformed. The development of analytical formulas relating structure para􀀐 meters and strain in each position inside the bulk sample is essential for a quantitative description of local changes induced by plastic deformation. Amount of grain surface (SV) and grain edge (LV) per unit volume are presented as the parameters for deformation description. As it is clear from previous work there are a few ways how to evaluate the grain orientation experimentally. However the most su􀀐 itable way in practice is the scalar measurement of anisotro􀀐 py based on stereological principle enabling to determine the degree of grains orientation. Anisotropic microstructure consists of (planar or linearly) oriented components which can be easily evaluated using stereological methods [6]. The results of such measurement can be converted to values of local deformation parameters. In that case it is sufficient to measure the degree of grains orientation to obtain a va􀀐 [...]

Verification of bulk metal forming numerical model

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Numerical models of metal forming based on finite elements method can lead to excellent results, but it is necessary to verify them by experimental results. The simple way as to verify numerical result is to compare them with experimental result. Bulk forming leads to grain boundaries deformation. The value of strain is very simple to obtain by stereology, more precisely - by measurement of grai[...]

Theoretical analysis of tube drawing process DOI:10.15199/24.2019.8.2


  Introduction. The production of precise seamless tubes is a complex problem because it is a complex process involving a lot of factors influencing the production processes and subsequent properties of drawn tubes. There are factors related to preparation of an initial material by continuous casting, hot forming of a pre-tube, cold forming of a tube connected with deformation strengthening, as well as the intermediate and final heat treatment operations. Due to this complexity, the paper is focused only on some problems of cold tube drawing process. Tube drawing [1-7]. During tube drawing a hot-rolled pre-tube is drawn through a die and its outer diameter is reduced. During fixed plug drawing not only the outer diameter of a tube is reduced but also its wall thickness. A coefficient of tube elongation λ is the drawing process characteristic. The λ coefficient can be determined from the law of volume constancy: ( ) ( ) r r r o o o r o o r D s s D s s S S L L - - λ = = = ⋅ ( 1) where: Lo, So, Do, so - length, cross section area, diameter and wall thickness of a tube before drawing, respectively, while Lr, Sr, Dr, sr - length, cross section area, diameter and wall thickness of a tube after drawing, respectively. At drawing with more than one draw, the total coefficient of elongation is detemined as: c n λ =λ ⋅λ ⋅λ ⋅ ⋅λ 1 ..... 2 3 ( 2) where: λc - total coefficient of elongation, λ1, λ2, λ3, λn - coefficient of elongation after the first, second, third and n-th draw, respectively. The tube drawing is divided into: - tube sinking - free tube drawing, - fixed plug drawing - with cylindrical or shaped plug, - floating plug drawing. The paper is focused on fixed plug drawing. Stress-strain states at fixed plug drawing. A schematic representation of stress and strain states in the three subsequent areas of the deformation[...]

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