Jakub Kõo

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

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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.
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.
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.
Thermal stresses in plates, cylinders and spheres with coatings : [full text in Russian]
(Eesti Põllumajanduse Akadeemia, 1977) Kõo, Jakub
Formulas for calculation of thermal stresses in plates, cylinders and spheres with coatings at uniform temperature variation are reduced.
Determination of residual stresses in cylinders with coatings : [full text in Russian]
(Eesti Põllumajanduse Akadeemia, 1977) Kõo, Jakub
Experimental determination of residual stresses in coated long hollow circular cylinders by measuring circumferential and longitudinal strains at material adding or removal is considered. Metrological equations for radial and circumferential residual stresses (6) and (7) are derived by using Lame´s formulas. Equation (10) for calculation of axial stress is obtained from the integral expression of the longitudinal force. Metrological equations (11) for a thin-shelled cylinder are presented.
Boundary effect in the case of deposition of the coating on a free edged thin-walled tube : [full text in Russian]
(Eesti Põllumajanduse Akadeemia, 1974) Kõo, Jakub
The boundary effect at deposition of a coating on a thin-walled tubular substrate with free edges is examined. Using the equation of radial displacements of the long cylindrical shell with a uniform moment load on the edge, it is shown that with a precision of 5% the boundary effect can be considered attenuated at a length according to expression (7) where r₁ , h₁ and h₂ are given by Fig. 1, k = h₂/h₁ and µ is the Poisson´s ratio which is identical for substrate and coating materials.
Once again about the force and deformation methods for determination of residual stresses in clamped bars and plates with coatings : [full text in Russian]
(Eesti Põllumajanduse Akadeemia, 1971) Kõo, Jakub
Metrological equations for the indicated experimental methods are presented for rigidly clamped and slipping clamped substrates. It is pointed out that the equations derived remain valid when the layer adding or layer removal techno-logy is applied.
Investigation of residual stresses in electrodeposits by strain measurement of a thin-walled tubular cathode : [full text in Russian]
(Eesti Põllumajanduse Akadeemia, 1969) Kõo, Jakub
A method for experimental determination of residual stresses in electro-deposits is described. According to this method a deposit to be investigated is deposited on the external surface of a thin-walled tubular cathode (Fig. 4) placed in a tank with rotating anodes (Fig. 3). At the same time, by using electrical-resistance strain gauges on the internal surface of the cathode strains are measured as a function of variable deposit thickness. Initial stress and residual stresses are determined via approximation of experimental information, applying the method of averaged sum. Determination of elastic constants of the substrate and coating materials is described. Technological problems of strain measurement are considered. An example of the processing of measurement data is presented. Initial stresses are determined for a number of cathode materials and galvanic iron coatings (Table 3).
Determination of Eigenstresses in Machine Elements Restored by Galvanic Coatings : [Autoreferat for the degree of Candidate of Engineering Sciences : full text in Russian]
(Leningrad Agricultural Institute, 1965) Kõo, Jakub
Extended summary of thesis for the degree of Candidate of Engineering Sciences): [full text in Russian]. This thesis of J. P. Kõo (Supervisor: Professor, Doctor of Engineering Sciences S. G. Gutman) for the degree of Candidate of Engineering Sciences is completed at Leningrad Agricultural Institute and at Estonian Agricultural Academy in 1957- 1965. The following research results are obtained: 1. A survey of the studies focusing on experimental techniques for determination of eigenstresses (henceforth residual stresses) in galvanic coatings is provided. 2. An algorithm for determination of residual stresses in machine elements restored by addition of galvanic coatings is proposed. 3. Presence of an equibiaxial state of residual stress in the superficial layer of a galvanic coating is established [8]. 4. A classification of galvanic coatings onto thin and thick coatings is offered. 5. Algorithms for calculation of residual stresses in plates coated at fixed, slipping or free edges are developed [5] (extension of the work of Stoney [2] and of Brenner and Senderoff [3). In particular, for a free plate substrate with unilateral coating for the deformation and the curvature measuring methods Stoney´s differential formulas are extended (see(Egs.(15)) and their integration is considered. 6. Problems related to determination of residual stresses in cylinders [6] and spheres [7] at application of galvanic coatings are solved. 7. Formulas for calculation of thermal stresses in galvanically covered plates, cylinders and spheres are established. 8. Techniques for determination of the initial stress (stress in the superficial layer) of a coating from deformation parameters measured at application of the coating are critically examied. 9. A new technique for experimental determination of initial stress is developed [9]. According to this, a coating to be investigated will be applied on the external surface of a thin-walled tubular cathode (see Fig.5). 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 (see Fig.6). Initial stress is determined (see Table 2) via approximation of experimental information by Eq.(19). 10. Examples of investigation of residual stresses for some details restored with the help of an iron galvanic coating are presented.
Determination of eigenstresses in electrodeposits by deformation of a thin-walled tube cathode: [full text in Russian]
(Eesti Põllumajanduse Akadeemia, 1963) Kõo, Jakub
A 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.

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