Jakub Kõo

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

Sirvi

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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.
Determination of Residual Stresses in Brush-Plated Coatings by Mechanical and X-ray Techniques
(Linköping University, 1997) Lille, Harri; Kõo, Jakub; Haav, Aksel
The 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.
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.
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 University
A 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.
Determination of Residual Stresses in the Coat Deposited bt Brush Plating
(DGM Informationsgesellschaft, 1993) Lille, Harri; Kõo, Jakub; Valgur, Jaak; Estonian Agricultural University
The 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.
Modelling of Residual Stresses by Photoelastic Method during the Coating Deposition
(DGM Informationsgesellschaft, 1993) Kõo, Jakub; Lille, Harri; Valgur, Jaak; Idnurm, Siim; Estonian Agricultural University
A calculating scheme according to which the process of material growth is regarded as a continuous growth of the equidistant to interface elementray layers with initial stresses is widely used for determination of residual stresses in coatings (1)-(5). Since the experimental confirmation of reliability of this scheme is missing, an attempt to model the formation of stress state in the grown bar by photoelastic method has been undertaken by the authors. The research carried out confirms the validity of the scheme of continuous growth in layers and the well-known Saint-Venant´s principle.
Modelling of the bending of a coated straigth strip substrate : [full text in Russian]
(Eesti Põllumajanduse Akadeemia, 1988) Kõo, Jakub; Lille, Harri
In the present paper the following problems are addressed: 1) bending of a plate at coating growth or removal; 2) bending of a plate with coating at temperature variation troughout thickness; 3) bending of a plate with a coating loaded by concentrated forces; 4) thermoelastic modelling of the bending of a coated straigth strip substrate by using thermoelastic bimetallic strips. It was found that at coating growth or removal the composite substrate- coating with a relative width of b/l= 0.05-0.5 bends like a plate that is non-homogeneous troughout thickness and is subjected to uniformly distributed edge moments (pure bending). However, in the case of a concentrated moment, the same substrate-coating behaves like a nonhomogeneous beam.
On Determination of Residual Stresses in Deposits by Measuring the Bending of a Thin-Walled Substrate in the Form of a Curvilinear Strip
(Copenhagen : Danmarks Tekniske Højskole, 1990) Kõo, Jakub; Lille, Harri
The paper deals with a perfected theory of determination of initial residual stresses in a deposit by measuring the angular deflection of free end of a substrate in the form of a helical warping strip. Unlike the theory based on the bar substrate model, proposed theory proceeds from the model of a cylindrical shell with curvilinear edges, that is asume existence of two-dimensional state of stress. Thus, the theory of Brenner and Senderoff´s spiral contractometer if defined more exactly. The determination of the initial residual stresses in the galvanic nickel deposit is given as an example.
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).
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.
Study of deformations of thermobimetallic straight strips under heating using the holographic interferomentry method : [full text in Russian]
(Киев : Наукова думка, 1991) Kõo, Jakub; Lille, Harri; Smirnov, V; Meštšerjakov, A
The method of interference holography is used to study deformation of plane thermobimetallic springs under uniform variation of temperature. It is established that free springs with thickness/width ration 1/20 and width/length ratio 1/5 are bent like plates by the spherical surface. Formulas for calculation of springs of normal bimetal are recommended.

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