Jakub Kõo
Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/7087
Sirvi
Sirvi Jakub Kõo Autor "Estonian Agricultural University" järgi
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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 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 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 Modelling of Residual Stresses by Photoelastic Method during the Coating Deposition(DGM Informationsgesellschaft, 1993) Kõo, Jakub; Lille, Harri; Valgur, Jaak; Idnurm, Siim; Estonian Agricultural UniversityA 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.Kirje On the Determination of Residual Stress in Coatings from Measured Longitudinal Deformation of a Substrate([Warsaw University of Technology], 2000) Kõo, Jakub; Ryabchikov, Alexander; Estonian Agricultural UniversityA method of measuring longitudinal deformation for determination of residual stresses in a long homogeneous cylinder by removal of thin cylindrical concentric layers was proposed by Heyn an Bauer [1]. In [2-6] it is shown that computation of residual stresses is possible from the longitudinal deformation of a cylindrical substrate, measured during coating deposition. The present paper presents a generalized theory of the method of measuring the longitudinal deformation of a long cylindrical substrate for determination of initial residual stresses in coatings. Unlike in [2-6], the possibility of prestressing the substrate by an elastic element (spring) is taken into account [7]. Special cases like (1) Poisson´s rations of the substrate and coating are equal, (2) Poisson´s ratios and the moduli of elasticity of the substrate and coating are equal, (3) a thin coating is applied on a rigid substrate, etc. are examined. A linear-fractional function is proposed for approximation of the dependence of initial stress on coating thickness.