Natalia Kosheleva - Academia.edu (original) (raw)
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Papers by Natalia Kosheleva
Sensors, 2021
The results of strain measuring experiments, with the help of rosettes consisting of fiber Bragg ... more The results of strain measuring experiments, with the help of rosettes consisting of fiber Bragg grating sensors (FBG) embedded at the manufacturing stage in a polymer composite material are considered in this paper. The samples were made by the direct pressing method from fiberglass prepregs. A cross-shaped sample was tested under loading conditions corresponding to a complex stress state. A variant of strain calculations based on experimental data is discussed. The calculations were performed under the assumption of a uniaxial stress state in an optical fiber embedded in the material. The obtained results provide a reasonable explanation of the absence in the conducted experiment of two peaks in the reflected optical spectrum, the presence of which follows from the known theoretical principles. The experimental result with two peaks in the reflected optical spectrum was obtained for the same sample under a different loading scheme. The proposed variant of the numerical model of th...
Frattura ed Integrità Strutturale, 2019
In this work, samples from composite materials with embedded optical fibers are investigated. It ... more In this work, samples from composite materials with embedded optical fibers are investigated. It is known that for unidirectional layered composite materials a distortion of the internal structure and the formation of such technological defect as resin pocket in the region of the embedded optical fiber occur under certain conditions. So it is important to evaluate the change in the internal structure for other types of reinforcement, in particular, woven reinforcement. Analysis of the internal structure of the studied materials with 22 twill weave style was carried out using a digital microscope. In addition, the reflected optical signal from the Bragg gratings after being embedded into the composite material is analyzed.
Procedia Structural Integrity, 2019
In the paper the problem associated with the use of fiber-optic strain sensors based on Bragg gra... more In the paper the problem associated with the use of fiber-optic strain sensors based on Bragg gratings glued to the surface of the material for the defects registration and their development was studied. The first part of the work is devoted to the numerical and experimental estimation of the error of strain values calculated on the basis of information on physical quantities recorded by sensors. In the second part of the work, a method for defects registration for a given external loads is presented. A background of the technique is the Saint-Venant principle, according to which the change in the strain values with the appearance of a defect occurs in the area defined by 3-5 characteristic defect sizes. Based on this, in order to register a defect without preliminary information about the strain distribution, it is necessary to provide in the observed object a strains measurement by the sensors that form a spatial grid with a step of 3 to 5 sizes of the expected defect. Last can be practically unrealistic. In the framework of the considered methodology, based on the results of numerical simulation, the sensors are located in stress concentration zones and areas with moderate stress concentration. Further, in the object without defects on the basis of numerical or experimental data, all variants of the relationships of the strain values obtained by two different sensors are recorded. The change in the monitoring process at least of one of these relationships allows to make a conclusion about the defect appearance as well as its location and evolution. The effectiveness of the technique is illustrated on a sample of a polymer composite material, in which holes of different diameters are made, imitating the appearance and development of a defect.
Frattura ed Integrità Strutturale, 2019
One of the issues in the strain measurement with the help of fiber-optic sensors based on Bragg g... more One of the issues in the strain measurement with the help of fiber-optic sensors based on Bragg gratings is the calculation of the strain based on the information from the sensor and its correspondence to the material strain. Relationships between the data measured by the sensor and the strain in the Bragg grating have a unique solution under the condition of uniaxial stress state of the fiber, which are not fulfilled when the fiber is embedded in the material. The paper presents the results of numerical simulations with an example of a model problem for a polymer composite material with an embedded optical fiber, which can be surrounded by a resin pocket. The presented results allow to estimate the error of the strain values calculated on the basis of uniaxial stress state assumption of the optical fiber. Based on numerical calculations, parameters of a capillary on an optical fiber in the Bragg grating zone are estimated, ensuring uniaxial stress state of the fiber in the Bragg grating zone. To ensure these conditions, the cross section of the capillary in an isotropic material is a circle, and in an anisotropic material, good results can be obtained with an elliptical cross section.
Open Journal of Metal, 2013
The technological principles of low-temperature superconductor production for the magnetic system... more The technological principles of low-temperature superconductor production for the magnetic system of the International Thermonuclear Experimental Reactor (ITER) that provides continuity of a superconductor billet in the superconductor production are considered.
The International Journal of Multiphysics, 2015
Within the past few years robust superconductor known as Secondgeneration (2G) High Temperature S... more Within the past few years robust superconductor known as Secondgeneration (2G) High Temperature Superconductor (HTS) were developed for different industrial applications. Their fabrication includes a phase of large bending, which induces both axial and shear stresses, which could lead to the degradation of the super-conductive substrate. The design of HTS requires analysis of the stress and strains induced during their fabrication. The use of the finite element method for the analysis of this complex material requires large meshes and computation time, because of the ultra-small thickness of the supra-conductive substrate. In this paper, we present a simplified model, which is based on the classical beam theory together with the discretization of each layer in small sub-layers working under purely axial stress. The model takes into consideration the plastic behaviour of the HTS constitutive materials. The model is validated by its confrontation to finite element analyses. Then it is used for the optimal design of HTS by the analysis of different industrial configurations. Analyses lead to some recommendations concerning the optimal configurations that reduce the stresses in the supra-conductive substrate.
Within the past few years, robust superconductors known as second-generation high-temperature sup... more Within the past few years, robust superconductors known as second-generation high-temperature superconductor (HTS) tapes were developed for different industrial applications. For some of them, it is necessary to transform the flat shape of the tape into a cylindrical one. It requires special fabrication steps that include phases of large-scale bending, which induce both axial and shear stresses. It could lead to the degradation of the superconductive layer. The manufacturing process of an HTS cylindrical wire requires some analysis of stress and strain induced during fabrication. The selected process also defines the initial tape architecture. The use of the finite-element method for the analysis of the model of this complex material requires fine meshes and a lot of computation time because of the ultrathin size of the superconductive layer. In this paper, we present a simplified model, based on the classical beam theory, along with the subdivision of each layer into small sublayers affected by purely axial stress. The model is created with consideration of the plastic behavior of the HTS tape consisting of different materials. The model has been validated by its comparison with finite-element analyses on simplified cases. Then, it was used to improve the optimal design of the HTS tape on the basis of analysis of different wires used in industry. According to the analysis, some recommendations on the optimal architecture reducing the stresses in the superconductive layer, have been given.
Sensors, 2021
The results of strain measuring experiments, with the help of rosettes consisting of fiber Bragg ... more The results of strain measuring experiments, with the help of rosettes consisting of fiber Bragg grating sensors (FBG) embedded at the manufacturing stage in a polymer composite material are considered in this paper. The samples were made by the direct pressing method from fiberglass prepregs. A cross-shaped sample was tested under loading conditions corresponding to a complex stress state. A variant of strain calculations based on experimental data is discussed. The calculations were performed under the assumption of a uniaxial stress state in an optical fiber embedded in the material. The obtained results provide a reasonable explanation of the absence in the conducted experiment of two peaks in the reflected optical spectrum, the presence of which follows from the known theoretical principles. The experimental result with two peaks in the reflected optical spectrum was obtained for the same sample under a different loading scheme. The proposed variant of the numerical model of th...
Frattura ed Integrità Strutturale, 2019
In this work, samples from composite materials with embedded optical fibers are investigated. It ... more In this work, samples from composite materials with embedded optical fibers are investigated. It is known that for unidirectional layered composite materials a distortion of the internal structure and the formation of such technological defect as resin pocket in the region of the embedded optical fiber occur under certain conditions. So it is important to evaluate the change in the internal structure for other types of reinforcement, in particular, woven reinforcement. Analysis of the internal structure of the studied materials with 22 twill weave style was carried out using a digital microscope. In addition, the reflected optical signal from the Bragg gratings after being embedded into the composite material is analyzed.
Procedia Structural Integrity, 2019
In the paper the problem associated with the use of fiber-optic strain sensors based on Bragg gra... more In the paper the problem associated with the use of fiber-optic strain sensors based on Bragg gratings glued to the surface of the material for the defects registration and their development was studied. The first part of the work is devoted to the numerical and experimental estimation of the error of strain values calculated on the basis of information on physical quantities recorded by sensors. In the second part of the work, a method for defects registration for a given external loads is presented. A background of the technique is the Saint-Venant principle, according to which the change in the strain values with the appearance of a defect occurs in the area defined by 3-5 characteristic defect sizes. Based on this, in order to register a defect without preliminary information about the strain distribution, it is necessary to provide in the observed object a strains measurement by the sensors that form a spatial grid with a step of 3 to 5 sizes of the expected defect. Last can be practically unrealistic. In the framework of the considered methodology, based on the results of numerical simulation, the sensors are located in stress concentration zones and areas with moderate stress concentration. Further, in the object without defects on the basis of numerical or experimental data, all variants of the relationships of the strain values obtained by two different sensors are recorded. The change in the monitoring process at least of one of these relationships allows to make a conclusion about the defect appearance as well as its location and evolution. The effectiveness of the technique is illustrated on a sample of a polymer composite material, in which holes of different diameters are made, imitating the appearance and development of a defect.
Frattura ed Integrità Strutturale, 2019
One of the issues in the strain measurement with the help of fiber-optic sensors based on Bragg g... more One of the issues in the strain measurement with the help of fiber-optic sensors based on Bragg gratings is the calculation of the strain based on the information from the sensor and its correspondence to the material strain. Relationships between the data measured by the sensor and the strain in the Bragg grating have a unique solution under the condition of uniaxial stress state of the fiber, which are not fulfilled when the fiber is embedded in the material. The paper presents the results of numerical simulations with an example of a model problem for a polymer composite material with an embedded optical fiber, which can be surrounded by a resin pocket. The presented results allow to estimate the error of the strain values calculated on the basis of uniaxial stress state assumption of the optical fiber. Based on numerical calculations, parameters of a capillary on an optical fiber in the Bragg grating zone are estimated, ensuring uniaxial stress state of the fiber in the Bragg grating zone. To ensure these conditions, the cross section of the capillary in an isotropic material is a circle, and in an anisotropic material, good results can be obtained with an elliptical cross section.
Open Journal of Metal, 2013
The technological principles of low-temperature superconductor production for the magnetic system... more The technological principles of low-temperature superconductor production for the magnetic system of the International Thermonuclear Experimental Reactor (ITER) that provides continuity of a superconductor billet in the superconductor production are considered.
The International Journal of Multiphysics, 2015
Within the past few years robust superconductor known as Secondgeneration (2G) High Temperature S... more Within the past few years robust superconductor known as Secondgeneration (2G) High Temperature Superconductor (HTS) were developed for different industrial applications. Their fabrication includes a phase of large bending, which induces both axial and shear stresses, which could lead to the degradation of the super-conductive substrate. The design of HTS requires analysis of the stress and strains induced during their fabrication. The use of the finite element method for the analysis of this complex material requires large meshes and computation time, because of the ultra-small thickness of the supra-conductive substrate. In this paper, we present a simplified model, which is based on the classical beam theory together with the discretization of each layer in small sub-layers working under purely axial stress. The model takes into consideration the plastic behaviour of the HTS constitutive materials. The model is validated by its confrontation to finite element analyses. Then it is used for the optimal design of HTS by the analysis of different industrial configurations. Analyses lead to some recommendations concerning the optimal configurations that reduce the stresses in the supra-conductive substrate.
Within the past few years, robust superconductors known as second-generation high-temperature sup... more Within the past few years, robust superconductors known as second-generation high-temperature superconductor (HTS) tapes were developed for different industrial applications. For some of them, it is necessary to transform the flat shape of the tape into a cylindrical one. It requires special fabrication steps that include phases of large-scale bending, which induce both axial and shear stresses. It could lead to the degradation of the superconductive layer. The manufacturing process of an HTS cylindrical wire requires some analysis of stress and strain induced during fabrication. The selected process also defines the initial tape architecture. The use of the finite-element method for the analysis of the model of this complex material requires fine meshes and a lot of computation time because of the ultrathin size of the superconductive layer. In this paper, we present a simplified model, based on the classical beam theory, along with the subdivision of each layer into small sublayers affected by purely axial stress. The model is created with consideration of the plastic behavior of the HTS tape consisting of different materials. The model has been validated by its comparison with finite-element analyses on simplified cases. Then, it was used to improve the optimal design of the HTS tape on the basis of analysis of different wires used in industry. According to the analysis, some recommendations on the optimal architecture reducing the stresses in the superconductive layer, have been given.