Jakub Kõo

Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/7087

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Nüüd näidatakse 1 - 20 58

Measurement of residual stresses in the cold-rolled Fe-Ni-Mn/Invar thermo-bimetallic plate
(Trans Tech Publications Ltd, 2026) Lille, Harri; Kõo, Jakub; Valgur, Jaak; Ryabchikov, Alexander; Reitsnik, Renno; Veinthal, Renno
The paper presents a method for measuring residual stresses in normal thermo-bimetal Fe-Ni-Mn/Invar strips with a thickness of 0.76 mm. For this purpose, a setup was designed which permits to remove layers from a strip substrate by electrochemical etching. Residual stresses in the directions that are longitudinal and transversal to rolling are determined by the curvature method based on the layer growing/removing techniques. As a reference, residual stresses were also determined by hole-drilling technique. Tensile and compressive residual stresses arose both in active and in passive layers and were considerably higher when determined by the hole-drilling technique.
Measurement of Residual Stresses in Electrochemically Metallized Coatings on Thin Cross-Cut Ring Substrate
(Trans Tech Publications Ltd, 2026) Lille, Harri; Kõo, Jakub; Ryabchikov, Alexander; Pihl, Toomas
An experimental method was developed for determination of residual stresses in electrochemically metallized (brush-plated) coatings by measuring the slit increment of the unclosed ring strip substrate after deposition process. The substrate is fixed to a mandrel, which makes free slipping of the edges as well as momentless deformation of the coated substrate possible. The calculation formula is extended Stoney’s formula which takes into consideration the real shape of the substrate, and the difference of the elasticity moduli of the coating and the substrate materials. The difference between the coefficients of thermal expansion of the coating and substrate materials is also taken into account. Residual stresses are determined for four materials (nickel, zinc, copper, silver) from six electrolytes.
Layer Growing/Removing Method for Determination of Residual Stresses in Thin Orthotropic Inhomogeneous Discs
(Trans Tech Publications Ltd, 2026) Kõo, Jakub; Valgur, Jaak
An algorithm of the layer growing/removing method for computing of the residual stresses in thin orthotropic inhomogeneous circular disc is presented. The stresses are calculated from strain measurements on the free stationary contour or on the lateral surface, or from X-ray diffraction measurements on the disc’s moving contour. The suggested algorithm is programmed for PC. Two illustrative examples are presented.
Bestimmung von Eigenspannungen in Bimetallstäbe und –Platten
(Eesti Põllumajandusülikool, 1995) Kõo, Jakub; Somelar, Jaanus
In diesem Beitrag wird die Theorie der verallgemeinerne mechanische Eigenspannungsmessmethode dargestellt.
Algkõverusega bimetallriba termodeformatsioonide uurimine
(Eesti Põllumajandusülikool, 1995) Kõo, Jakub; Lille, Harri
Artiklis uuritakse teoreetiliselt ja katseliselt pikisuunalise algkõverusega bimetallriba ühtlasest temperatuuri muutusest põhjustatud piki- ja põikkõverust. Nende määramiseks on tuletatud arvutusvalemid. Katsed teostati normaalsest termobimetallist valmistatud proovikehadega. Toodud valemitega arvutatud tulemused on rahuldavas kooskõlas katsandmetega.
Pindega õhukeseseinalise rõnga deformatsiooni uurimine lahtilõikamisel
(Eesti Põllumajandusülikool, 1995) Kõo, Jakub; Lille, Harri
Artiklis uuritakse pindega rõnga läbilõikamisel tekkiva pilu muutust sõltuvalt laiusest. Koorikute tehnilise teooria baasil on tuvastatud, et laiad bimetallrõngad deformeeruvad ~30% enam kui kitsad. Tulemuse kontrollimiseks teostati katsed, kus õhukeseseinalisele valgevasktorule sadestati galvaaniliselt nikkelpinne. Toru tükeldati erineva laiusega rõngasteks, millised seejärel lõigati takistatud painde tingimustes piki moodustajat lahti ning mõõdeti tekkinud pilu muut. Saadud mõõtetulemuste kokkulangevus arvutustulemusega oli rahuldav.
Layer growing/removing method for determination of residual stresses in orthotropic non-homogeneous cylinders
(International Centre for Diffraction Data, 2009) Kõo, Jakub; Valgur, Jaak
A unique algorithm of layer growing/removing methods for computing of the residual stresses in the incompletely orthotropic layered circular cylinder is presented. The stresses are calculated from strain measurements on the free stationary surface or from strain measurements on the cylinder's moving surface. The suggested algorithm is programmed for PC. As an illustrative example, residual growth stresses in a stem of Japanese red pine are computed from initial stresses measured on its free outer surface.
Residual stress measurement in goated plates using layer growing/removing methods: 100th anniversary of the publication of Stoney's paper "The tension of metallic films deposited by electrolysis"
(Trans Tech Publications Ltd, Switzerland, 2011) Kõo, Jakub; Valgur, Jaak
In connection with the 100th anniversary of Stoney's equations, some historical remarks are made with respect to the development of these equations. As an example of the extension of Stoney's equations, a unique algorithm of the layer growing/removing methods is presented for determination of residual stresses in isotropic inhomogeneous coated plates. Using a computer program based on this algorithm, residual stresses are computed in the galvanic steel coating on the copper plate substrate.
Extension of Kübler's model for analysis of growth stresses in tree disc
(University of Tartu Press, 2015) Kõo, Jakub; Valgur, Jaak
The layer growing/removing method for determination of residual stresses in orthotropic non-homogeneous discs has been applied as an extension of Kübler's model for analysis of growth stresses in the tree disc. The extended model permits to take account of the orthotropic characteristics and the layered structure of the tree disc. As an illustrative example, growth stresses are calculated in a disc of spruce wood from initial (maturation) stress measured on its free outer surface.
Determination of residual stresses in coated plates using layer growing/removing methods: 100th anniversary of Stoney’s equations
(Tallinn University of Technology, 2010) Kõo, Jakub; Valgur, Jaak
In connection with the 100th anniversary of Stoney’s equations, some historical remarks are made with respect to the development of these equations. In the capacity of an example of the extension of Stoney’s equations, a unique algorithm of the layer growing/removing methods for determination of residual stresses in isotropic inhomogeneous coated plates is presented. Using a computer program based on this algorithm, residual stresses are computed in a detonation gun sprayed WC-Co coating.
Determination of Eigenstresses in Machine Elements Restored by Galvanic Coatings : [Dissertation for the degree of Candidate of Engineering Sciences : full text in Russian]
(Ленинградский сельскохозяйственный институт, 1965) Kõo, Jakub; Gutman, S. (juhendaja)
Autoreferat of the thesis is available http://hdl.handle.net/10492/8534
Determination of residual stresses in deposits by measuring the deformation of a thin-walled ring-shaped substrate: [full text in Russian]
(Technische Hochschule Zwickau, 1989) Kõo, Jakub; Lille, Harri
A metrological equation is proposed for the indicated experimental method. In this case the substrate is considered to be a short cylindrical shell ( Fig.). The proposed equation permits calculation of surface stress (initial stress) from circumferential strain measured on the internal surface of the substrate by using of electrical-resistance strain gauges.
On the determination of surface stresses in coatings by means of axial strain measurement method of flat-sheet substrate: [full text in Russian]
(Ingenieurhochschule Zwickau, 1985) Kõo, Jakub; Lille, Harri
Metrological equations: exact variant (1) and approximate variant (2) are proposed for the indicated experimental method (see also Fig. 1). As an example, surface stresses (initial stresses) are calculated from the experimental data measured at deposition of a galvanic cobalt coating onto a platinum substrate [1]. The input and output data are presented in Fig. 2, where curves 1 describe the distribution of measured strain, curves 2 represent the distribution of determined surface stresses and curves 3 are calculated according to a formula from [2]. Solid curves correspond to coating growth, dotted curves correspond to coating removal.
On the determination of residual stresses in fibres using the axial strain measurement method: [full text in Russian]
(Институт механики полимеро, 1984) Kõo, Jakub
In comparison with the methods recommended in papers [1, 2], according to which the state of stress of coated fibres is considered uniaxial, the developed method makes it possible to determine all three principal stresses of the residual stress state.
On the determination of residual stresses in the deposits applied by brush plating : [full text in Russian]
(Ingenieurhochsch Zwickau, 1982) Kõo, Jakub; Lille, Harri
The method of described discontinuous growth enables to determine initial stress in brush plated coatings by the measured slit increment of a short thin-walled cylindrical cathode cut along the generator (Fig. 1). An integral approch is used for deduction of the metrological equation (16). As an example initial stress for a copper coating on a brass substrate is determined (Fig. 3).
Determination of residual stresses in the coatings of plates using the curvature measurement method : [full text in Russian]
(МГТУ им. Н. Э. Баумана, 1979) Kõo, Jakub
A general treatment of the method of measurement of the deformation parameters of a plate substrate with fixed edges at deposition of a unilateral coating is presented. Volterra´s first kind integral equation is obtained for determination of initial stress. The solution of this equation is found by its reduction to the differential equation. Presuming the linear fractional distribution of initial stress, a formula for approximation of experimental information is obtained. An illustrative example is presented.
On determination of residual stresses in coatings : [full text in Russian]
(МГТУ им. Н. Э. Баумана, 1976) Kõo, Jakub
An integral approach is used for derivation of a metrological equation for experimental determination of residual stresses in coatings of bars and plates using strain measurement. Equation (1) is Volterra´s first kind integral equation where elastic constants of substrate and coating materials are assumed to be different. From this equation, by means of its reduction to the differential equation and integration, the metrological equation (2) is obtained. Problems of measurement data processing are adressed. As an example, the results of processing of experimental data for a data collection are presented (Fig. 1).
On the method for determining residual stresses in hollow spheres : [full text in French]
(VDI-Verlag, 1976) Kõo, Jakub
Known Peiter´s method [1; 2] for experimental determination of residual stresses in homogeneous hollow spheres from the circumferential strain measured on the internal surface at addition or removal of material on the external surface is extended for a radially inhomogeneous sphere.
Determination of residual stresses in coatings of rigidly clamped rods and plates by measuring strain: [full text in Russian]
(Институт проблем прочности НАН Украины, 1975) Kõo, Jakub
Residual stresses in clamped rod and plate coatings can be determined by using a known method of deflection measurement, developed further in papers [2-7]. However, the wide application of strain gauges in modern measurement technology justifies in many cases the use of the proposed method. It is based on measurement of the strain arising on the free side of the substrate when the clamped edges becom free after building up the coatings up to required thicknesses. Metrological equations are derived and an example of determination of residual stress for a coating is presented.
Determination of residual stresses in bars and plates using the strain measurement method : [full text in Russian]
(МГТУ им. Н. Э. Баумана, 1969) Kõo, Jakub
An integral approach is used for derivation of a metrological equation for the indicated measurement method . The equation (1) is Volterra´s first kind integral equation from which, by means of its reduction to the differential equation and integration, metrological equation (4) is obtained. Problems of measurement data processing are addressed. As an example, determination of residual stresses in the galvanic iron coating of a plate-like cathode is presented.

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