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Utilization of finite fracture mechanics for correction of fracture toughness measurement on samples with various notch root geometry
Dohnal, Petr ; Majer, Zdeněk (referee) ; Ševeček, Oldřich (advisor)
The work deals with the use of numerical simulations and the theory of finite fracture mechanics for the analysis of conditions for the formation of a crack in a ceramic test sample with a notch (loaded by four-point bending) and possible ways of correcting the fracture toughness determined experimentally on samples with different notch root radius. For this purpose, a parametric calculation model was created to simulate the fracture toughness test by four-point bending. In the first step, the calculation of the critical force at which a crack occurs in a test specimen with a rounded notch and its subsequent unstable propagation through the remaining cross-section of the specimen was debugged. For this purpose, the finite element method (FEM) and the coupled stress-energy criterion were used. In the next step, the procedure of calculation of fracture forces was also applied to a set of experimental samples in order to compare the numerical prediction with experimentally measured values. Two methods of correction of the fracture toughness determined experimentally are also proposed in the thesis. One uses for a correction of the measured values numerical calculation using the coupled stress-energy criterion. In the second case, a correction function was derived using numerical simulation, which no longer needs an FEM calculation for its future use. Correction of the measured fracture toughness using the function proved to be better but not completely effective for the entire range of investigated notch root radii. When comparing with other correction functions found in the literature, it can be stated that the correction procedure proposed in the work provides a better agreement with the real value of the fracture toughness of the given material up to a certain value of the notch root radius.
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A study of the stress field near the stress concentrator at the bi-material interface
Krepl, Ondřej ; Klusák, Jan (referee) ; Profant, Tomáš (advisor)
The aim of this work is the solution of problems of the stress distribution near bimaterial notch tip or eventually the crack impinging orthogonaly the bimaterial interface, determination of stress singularity exponent. The first part is concerned with basics of linear elastic fracture mechanics, i.e. Irwin's concept of stress intensity factor. The second part is devoted to description of anisotropic materials by complex potencial theory. The final part is focused on calculation of eigenvalues of both isotropic and anisotropic materials and application of LES formalism on the calculation of stress singularities of the bimaterial ortotropic notch or the crack impinging orthogonaly the bimaterial interface.
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Stress concentrators in aircraft structures
Černota, Jiří ; Pejchar, Jan (referee) ; Augustin, Petr (advisor)
This bachelor´s thesis deals with significant stress concentrators in compossed plane constructions made of metal materials. It generates summary of the most significant notches and their effect on fatigue life. It further states opportunities of description of constructional solution leading to reduction of stress concentration.
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Stress concentrators in aircraft structures
Černota, Jiří ; Pejchar, Jan (referee) ; Augustin, Petr (advisor)
This bachelor´s thesis deals with significant stress concentrators in compossed plane constructions made of metal materials. It generates summary of the most significant notches and their effect on fatigue life. It further states opportunities of description of constructional solution leading to reduction of stress concentration.
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A study of the stress field near the stress concentrator at the bi-material interface
Krepl, Ondřej ; Klusák, Jan (referee) ; Profant, Tomáš (advisor)
The aim of this work is the solution of problems of the stress distribution near bimaterial notch tip or eventually the crack impinging orthogonaly the bimaterial interface, determination of stress singularity exponent. The first part is concerned with basics of linear elastic fracture mechanics, i.e. Irwin's concept of stress intensity factor. The second part is devoted to description of anisotropic materials by complex potencial theory. The final part is focused on calculation of eigenvalues of both isotropic and anisotropic materials and application of LES formalism on the calculation of stress singularities of the bimaterial ortotropic notch or the crack impinging orthogonaly the bimaterial interface.
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