Jakub Kõo
Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/7087
Sirvi
Sirvi Jakub Kõo Märksõna "articles" järgi
Nüüd näidatakse 1 - 20 34
Tulemused lehekülje kohta
Sorteerimisvalikud
Kirje Analysis of thermoelastic stresses in layered plates(Tallinn University of Technology, 2008) Kõo, Jakub; Valgur, JaakThis paper deals with thermoelastic effects in deformation of plates with arbitrarily changing elastic parameters and temperature through thickness. Using the semi-inverse method, a simple analytical solution is obtained for the thermoelastic problem of a nonhomogeneous plate with an arbitrary contour. Plates with free, sliding and fixed edges are considered. The results are applied to the layered plate. As an example of application, thermoelastic stresses and deformations are determined for a copper plate with a steel coating. The edge effects for this plate are examined by the finite element method.Kirje The application of the method of holographic interferometry by modelling the bending of a straight strip substrate with the deposit : [full text in Russian](Eesti Põllumajanduse Akadeemia, 1990) Kõo, Jakub; Lille, Harri; Smirnov, V.; Metšerjakov, M.The results of modelling of the bending of a straight strip substrate with a deposit by bending a thermobimetallic strip in the case of a regular change of temperature are presented. The deposit was added or removed on the surface of the substrates with a relative thickness of less than 0.08 and a relative width of more than 0.16. The deformed surface of the substrate determined by the method of holographic interferometry is spherical.Kirje Calculation of Eigenstresses in Electrodeposits by Deformation of a Thin Plate Cathode :[full text in Russian](Eesti Põllumajanduse Akadeemia, 1959) Kõo, JakubDraw on the analogy between a libre thermal strain in a elastic body and a libre eigenstrain in a electrodeposit, for calculation of eigenstress (residual stress) in the superficial layer of a galvanic coating, formula (4) is obtained, where En, µ and β are the modulus of elasticity for coating, Poisson´s ratio (identical for coating and substrate) and free linear eigenstrain in the coating superficial layer. I addition eigenstrain β is calculated from the experimentally determined curvature of the substrate. The correspondind calculation formulae are presented for a plate substrate with free edges (Fig. 1a): formula (8), for slipping edges (Fig.1b): formula (36) and for fixed edges (Fig.1v): formula (38). Substitution these formulae in formula (4) yields the corresponding formulae of Stoney [2] an Brenner-Senderoff [3] complemented by factor 1/(1-µ) which modifies the formulae under consideration through taking account of the biaxial state of stress in a coated plate cathode.Kirje Calculation of residual stresses in electrodeposited circular cylindres : [full text in Russian](Ленинградский сельскохозяйственный институт, 1961) Kõo, JakubThe axially symmetric problem of thermoelasticity for a circular multilayer cylinder is solved. Using this solution and basing on the analogy between libre thermal strain in an elastic body and libre eigenstrain in a galvanic coating, the problem of determination of residual stresses (eigenstresses) in a circular cylinder with a galvanic coating is solved. The compatibility problems of the solution are considered. As an example, the residual stress distributions, calculated by using equations (30) for a hollow cylindrical substrate with a coating, are presented in Fig.3.Kirje Calculation of residual stresses in electrodeposited spheres : [full text in Russian](Сельхозиздат, 1962) Kõo, JakubThe polar-symmetric problem of thermoelasticity for a multilayer sphere is solved. Using this solution and based on the analogy between a libre thermal strain in an elastic body and a libre eigenstrain in a galvanic coating, the problem of determination of residual stresses (eigenstresses) in a multilayer galvanically grown sphere is solved. The compatibility problem of the solution is considered. As an example, residual stresses are determined for a coating on a thin-walled spherical substrate (application of equations (38) and (51) which modify the Mills method [7]).Kirje Consideration of Thermal Stresses in Experimental Residual Stress Analysis for Coatings([Warsaw University of Technology], 2004) Kõo, Jakub; Ryabchikov, Alexander; Estonian Agricultural UniversityUsually, the coefficients of thermal expansion of the coating and substrate are different and the temperature of coating process differs from room temperature (20ºC). Therefore thermal stresses are generated in coated parts. In experimental analysis of residual stresses it may turn out that caoting temperature differs from the temperature at which the deformation parameters of the substrate are measured. In Susch cases the measurement results have to be corrected taking into account the thermal stresses. In this study, the equations for correction of the residual stresses in coatings, determined from the measured longitudinal deformations of the wire, and from the tubular and strip substrates [1-3], are presented. Three examples of application are given.Kirje Determination of eigenstresses in electrodeposits by deformation of a thin-walled tube cathode: [full text in Russian](Eesti Põllumajanduse Akadeemia, 1963) Kõo, JakubA new technique for experimental determination of initial stress was developed. According to this, a coating to be investigated will be applied on the external surface of a thin-walled tubular cathode (see Figs. 2, 3). In addition, by using of electrical-resistance strain gauges on the internal surface of the cathode, strains are measured as a function of variable coating thickness. Initial stress is determined via approximation of experimental information. As an example in Fig.4 the distributions of measured deformations and initial and eigen- stresses (residual stresses) for a galvanic steel coating of a thin-walled tubular cathode are presented.Kirje Determination of residual stresses in bars and plates using the strain measurement method : [full text in Russian](МГТУ им. Н. Э. Баумана, 1969) Kõo, JakubAn 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.Kirje Determination of Residual Stresses in Brush-Plated Coatings by Mechanical and X-ray Techniques(Linköping University, 1997) Lille, Harri; Kõo, Jakub; Haav, AkselThe determination of residual stresses is studied in brush-plated nickel coatings of different thickness, deposited on brass strip substrates with two different dimensions. Residual stresses in the surface layer were found by the deformation method, displacement of the free end of the coated region of the cantilevered strip substrate or the axial strain of the free surface serving as experimental information. The x-ray diffraction technique was employed to determine residual stresses in specimens (8x10 mm) cut from the middle of the coated strip substrate by using lattice parameters measured for two different ψ values. Comparable values of residual stresses, 350-450 MPa and 280-480 MPa, were obtained in coating with a thickness of 45-110 μm by using the mechanical method and the x-ray diffraction technique respectively.Kirje 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, JaakIn 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.Kirje 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, JakubResidual 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.Kirje 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, HarriA 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.Kirje Determination of Residual Stresses in Inhomogeneous Plates With Layer Growing/Removing Techniques([Warsaw University of Technology], 1998) Kõo, Jakub; Lille, Harri; Valgur, Jaak; Estonian Agricultural UniversityA generalized algorithm of the layer growing/removing methods is presented for computing residual stresses in a free rectangular isotropic inhomogeneous plate whose elastic parameters depend on its thickness coordinate. The algorithm allows calculation of residual stresses from initial stresses measured on the moving surface using X-ray diffraction. The suggested algorithm is programmed for PC and presents interest first of all in the study of residual stresses in coatings and surface layers generally. An example of application is presented.Kirje Determination of Residual Stresses in the Coat Deposited bt Brush Plating(DGM Informationsgesellschaft, 1993) Lille, Harri; Kõo, Jakub; Valgur, Jaak; Estonian Agricultural UniversityThe method of continuous growth described in the article enables the determination of initial stress in the brush plated coat by the circumferential strain of the short thin-walles cylindrical cathode. The Tihonov´s method of regularization could be reccommended as an effective method of approximation of experimental data and calculation of derivative.Kirje 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, JakubA 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.Kirje Eigenstresses in thin electrodeposits: [full text in Russian](Eesti Põllumajanduse Akadeemia, 1963) Kõo, JakubThe eigenstress (residual stress) state of a thin superficial layer of an electrodeposit is considered. The analysis is based on Ilyushin´s theory of plasticity. It is established that the state of stress in the superficial layer is equal biaxial compression or tension defined for the elastic state according to formula (9), for initial stress, where E, µ and β are the modulus of elasticity, Poisson´s ratio and initial strain for the coating, respectively. At β>0 there occurs biaxial compression, at β<0 there occurs biaxial tension. It is shown that eigenstresses (residual stresses) in the thick deposit are expressed as the sum of initial stress and additional stress.Kirje Extension of Kübler's model for analysis of growth stresses in tree disc(University of Tartu Press, 2015) Kõo, Jakub; Valgur, JaakThe 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.Kirje Layer Growing/Removing Method for the Determination of Residual Stresses in Inhomogeneous Cylinders(Linköping University, 1997) Kõo, Jakub; Valgur, Jaak; Estonian Agricultural UniversityAn algorithm of the layer growing/removing method is presented for computing residual stresses in case of the long multilayered hollow cylinder from strain measurements on the free stationary surface or from X-ray diffraction measurements on the cylinder´s moving surface. The algorithm is valid for layer growing/removing on the outer or inner surface of the cylinder and is of interest first of all in the study of residual stresses in coatings and surface layers generally. The suggested algorithm is programmed for PC. An example of application is presented.Kirje Layer Growing/Removing Method for the Determination of Residual Stresses in Inhomogeneous Spheres([Warsaw University of Technology], 1998) Kõo, Jakub; Valgur, Jaak; Estonian Agricultural UniversityA generalized algorithm of the layer growing/removing methods is presented for computing residual stresses in case of the multilayered hollow sphere from strain measurements on the free stationary surface or from X-ray diffraction measurements on the sphere´s moving surface. The algorithm is valid for layer growing/removing on the outer or inner surface of the sphere and is of interest first of all in the study of residual stresses in coatings and surface layers generally. The suggested algorithm is programmed for PC. Two examples of application are presented.Kirje Layer-Growing and Layer-Removing Methods for Residual Stress Analysis: General Algorithm(Société Française de Métallurgie et des Métaux, 1996) Kõo, JakubThis review paper presents an algorithm of layer-growing and layer-removing methods for the determination of residual stresses, which is of interest first of all in the study of residual stresses in coatings and in surface layers generally. The basis of the algorithm is a model of continuous growth in layers of an elastic body. The determination of residual stresses in a free plate with a unilateral caoting, and in a hollow cylinder and a sphere with an outer coating is considered. Two examples of application are presented.