Long term, his scientific and research activities are oriented to the field of technological prediction of formability of steel sheets with higher strength properties, testing of material properties of steel sheets, simulation of stamping processes, the evaluation of the technical-economic level of production and engineering products. Prof. Evin was the principal investigator of 4 VEGA and 1 APVV projects, co-partner of several national VEGA, APVV and international scientific research projects and dozens of projects for practice. B.Sc. and M.Sc. degree in the field of Mechanical Technologies at the same university in 2010 and 2012. His current field of interest is focused on the area of sheet metal forming, such as measurement and evaluation of deformation, simulation of sheet metal forming processes.Abstract: This In order to define the friction coefficient the simulator of strip drawn test between flat dies and cup test were applied. To evaluate the coefficient between flat dies the modified Coulumb law was used and for defining the friction at drawing edge of die the modified Ouehler formula was applied. Due to these both evaluation processes it was enabled to point out the difference of friction coefficient values in various contact areas of rolling product and the tool. In his paper there are presented the measurement and evaluation processes of friction coefficient by applying the cup test. For experimental research the following types of materials are suitable: DC 05-extra deep drawable steel sheet, DX 54D -extra deep drawable Zn coated steel sheet, austenitic steel sheet DIN 1.4301.
When numerically simulate the stamping processes, it is important to define the friction coefficients in different regions. These depend on the deformation processes due to various stress-strain states in each area. In the deep drawing process, the friction conditions in the blankholder-blank-die area and blank-die radius area differ. The analytical models for the friction coefficients determination by strip drawing test are presented in the paper. The equations have been used to calculate the friction coefficients based on a physical model of the strip drawing test and its numerical simulation. The physical and numerical experiments have been performed on Zn coated IF steel DX54D with thickness 0.78 mm. Hill48 yield law and Hollomon's hardening curve have been used as material characteristics when numerically simulated. The blank-holding forces 4 and 9 kN have been set during the experiment and numerical simulation. Good conformity of numerical simulation and the physical model have been found when friction coefficients were calculated from analytical models including the ratio of drawing forces measured with fixed and rotated cylinder. Additionally, the normal contact pressure under the blankholder and on the die radius was evaluated from the numerical simulations. The highest value has been found at the die radius start.
Materials other than standard and advanced high strength steels are remarkable for the thin-walled structures of the car-body in recent years in order to safety enhancement, weight and emission reduction, corrosion resistance improvement. Thus, there are presented in the paper the deformation properties of laser welded austenitic AISI 304 and ferritic AISI 430 stainless steels compared to these one measured for the high strength low alloyed steel H220PD. The properties were researched by tensile test and 3-point bending test with fixed ends on specimens made of basic material and laser welded one. The specimens were welded by solid state fiber laser YLS-5000 in longitudinal direction (the load direction). The deformation properties such as strength, stiffness and deformation work were evaluated and compared. The strength and stiffness were calculated from tensile test results and the deformation work was calculated from both, tensile test and 3-point bending test results. There has been found only minor effect of laser welding to the deformation properties for high strength low alloyed steel H220PD and austenitic stainless steel AISI 304. Otherwise, the laser welding strongly influenced the deformation work of the ferritic stainless steel AISI 430 as well as the elongation at tensile test.
The paper presents the findings of the strain rate effect, described in constitutive material models by strain rate sensitivity index m, to the strength and deformation material properties. These were evaluated from stress-strain diagrams recorded at tensile test using PC controlled testing machine TiraTEST 2300 according to STN EN ISO 6892-1. The high strength low alloyed steel H220PD, dual phase steel DP 600 and Trip steel RAK 40/70 were investigated at strain rates = 0.0021, 0.083 and 0.125 s -1 . The results indicate major influence of the strain rate to the strength properties while only minor influence have been found when evaluate the deformation properties. The results also shown single phase materials are more sensitive to the strain rate than dual phase materials.
The subject of this paper is an experimental stress analysis of a rotor with a symmetrical arm end and a rotor with an asymmetrical arm end. The main aim of this paper is to test the application of the Harmonic Star Method software developed by the authors. This software analyzes stress states in rotating structural elements. The stress state of the analyzed rotors is caused by centrifugal forces. The experiment was carried out by means of reflection photoelasticity, and the experimental solution was focused on periodical dynamic effects, which required the use of stroboscopic white light. The resulting principal normal stresses were compared with stress values, which were obtained by analytical calculations and by numerical means of the finite element method.
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