Browsing by Author "Pešek, Ladislav"

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    Comparison Of Deformation Characteristics Of The Steel Sheet In Local And Global Area By The Static Loading Using Videoextensometry
    (Chemické Listy, 2011-01-01) Hlebová, Stanislava; Pešek, Ladislav; Kandra, Tomáš
    Two steel sheets used for deep drawing of the compressor cover were investigated using the videoextensometry technique for strain monitoring during tensile test. The material causing cracks during deep drawing has higher both yield stress and strength and lower ductility comparing with material without problems in technology. The strain hardening exponent n is increasing in the strain interval up to just before R-m, while the values measured in local area were lower than values measured in global area. The plastic strain ratio is decreasing for both materials measured in local and global area.
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    Determination of Plastic Zone by UCI Technique on Thin Steel Sheets
    (2010-01-01) Ambriško, Ľubomír; Pešek, Ladislav; Hlebová, Stanislava
    The main goal of this paper is the determination of the size and shape of the plastic zone in thin steel sheets. The aim of experiments was to analyze the influence of the material and type of the initial crack on the dimensions of the plastic zone. The plastic zone size and shape is also predicted by measuring hardness (HV 1) along and across the unbroken ligament. The hardness is measured by using UCI (Ultrasonic Contact Impedance) technique. The hardness values varied in dependence on the material and the initial crack. In this paper, the CT (Compact Tension) specimens of two steel grades with a notch and with an electrospark produced notch were used. Specimens were loaded by eccentric tension, whereby the deformation in the area around the notch was recorded by non-contact displacement measurement - a videoextensometry technique.
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    Measurement of the steady state tearing in thin sheets using the contactless system
    (EDP SCIENCES S A, 17, AVE DU HOGGAR, PA COURTABOEUF, BP 112, F-91944 LES ULIS CEDEX A, FRANCE, 2020-06-01) Ambriško, Ĺubomír; Pešek, Ladislav
    The purpose of the present paper is the diagnostic method of the steady state tearing tests in thin steel sheets. The camera-based contactless system was used in the experimental research. The MATLAB software was used for the processing of real-time images. The data collected in the experiments were used to establish the R-curves in terms of the CTOD (crack tip opening displacement) based resistance curves. The innovative techniques allow extracting a large amount of geometrical information about the entire tearing process and the crack tip development. The steady state tearing was evaluated using automotive steel sheets and the tearing resistance was determined for three grades of thin sheets. The paper describes a comprehensive method of obtaining the material properties necessary for modelling and simulation. The proposed methodology for the testing and evaluation of the steady state tearing is applicable to thin sheets. The measurement method within the test for the determination of the tearing resistance was based on the image analysis.
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    Modelování globálních mechanických vlastností na základě experimentálního stanovení vlastností lokálních
    (Technická Univerzita v Liberci, 2016-01-01) Burik, Peter; Pešek, Ladislav
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    Prediction of tensile properties based on hardness measurement
    (Trans Tech Publications Ltd, 2014-01-01) Zubko, Pavol; Pešek, Ladislav
    The contribution deals with prediction of tensile properties based on measurement of microhardness. First of all, the database of stress - strain, σ-ε vs. hardness data was created. Tensile strength, yield strength, ductility and parameters of Ludwik-Hollomon equation σ = σ0+kεn ; k, n were correlated with hardness. Various hardness values found in literature were recalculated to Brinell hardness. In tensile testing measured σ-ε curves were compared with that obtained from the correlation. The investigated materials were API 5 L grade steels - X70 after different deformation levels. The results give good agreement between compared data. The most significant difference between estimated and measured curve is in area of yield strength, because of Lüders deformation on investigated steel. © (2014) Trans Tech Publications, Switzerland.