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Influence of torsional pre-strain on fracture characteristics under tensile loading
Kupka, Oldřich ; Majer, Zdeněk (referee) ; Horníková, Jana (advisor)
The diploma thesis is about the influence of torsional pre-strain on fracture characteristics under tensile loading of steel 11 375. Plastic strain in the cross-section of tested specimen is caused by torsional pre-strain. Plastic strain causes a different response of a material to tensile loading. A smooth tensile test specimen and tensile test specimen with a notch are examined. The research part of thesis describes tensile and torsional tests according to regular standarts. The nonlinearities considered in computational models are also described, followed by a description of material models in the software Ansys, which is used to create the computational model. Mechanisms of failure, the importance of stress triaxiality and the construction of triaxiality space are also introduced to a reader. The first experiment is about a tensile test of steel 11 375. The stress-strain curve obtained by the tensile test will be used as input in computational modelling. The aim of computational modelling is the determination of torsional pre-strain, that causes plastic strain in a tested specimen. The true stress field, true strain field and points of triaxiality space are determined by computational models. During the second experiment, tensile test specimens are torsioned according to outputs of computational models, followed by a tensile load to fracture. The main output of the experiment is fracture engineering strain. Finally, the stress-strain curves of computational models are also compared with experimental measurements.
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Elastoplastic analysis of stress and deformation and determination of fracture parameters of bodies with stress concentrators under tensile loading
Dubravec, Kristián ; Majer, Zdeněk (referee) ; Horníková, Jana (advisor)
The aim of this thesis is the construction of a diagram of fracture strain for high strength steel OCHN3MFA and its application for the estimation of fracture toughness of this material. The first part of the thesis contains the necessary theoretical framework for numerical modelling of tensile tests of various specimens - smooth specimen, specimen with a notch and specimen with a circumferential crack, it describes the influence of triaxiality on the fracture of bodies and the possibilities of construction of the diagram of fracture strain. Subsequently, a numerical model of these specimens is created using the finite element method (FEM). A non-linear, elastoplastic calculation is performed. Fracture is identified by means of comparing the true stress versus the strain obtained from tests with the finite element analysis results. Stress–strain states of specimens at the moment of fracture are obtained from a numerical model. A diagram of fracture strain is constructed, and it is used to estimate the fracture toughness of a cracked body. Finally, a local approach, which uses the diagram of fracture strain, and a classical approach of fracture mechanics, especially the stress intensity factor, are compared.
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Influence of torsional pre-strain on fracture characteristics under tensile loading
Kupka, Oldřich ; Majer, Zdeněk (referee) ; Horníková, Jana (advisor)
The diploma thesis is about the influence of torsional pre-strain on fracture characteristics under tensile loading of steel 11 375. Plastic strain in the cross-section of tested specimen is caused by torsional pre-strain. Plastic strain causes a different response of a material to tensile loading. A smooth tensile test specimen and tensile test specimen with a notch are examined. The research part of thesis describes tensile and torsional tests according to regular standarts. The nonlinearities considered in computational models are also described, followed by a description of material models in the software Ansys, which is used to create the computational model. Mechanisms of failure, the importance of stress triaxiality and the construction of triaxiality space are also introduced to a reader. The first experiment is about a tensile test of steel 11 375. The stress-strain curve obtained by the tensile test will be used as input in computational modelling. The aim of computational modelling is the determination of torsional pre-strain, that causes plastic strain in a tested specimen. The true stress field, true strain field and points of triaxiality space are determined by computational models. During the second experiment, tensile test specimens are torsioned according to outputs of computational models, followed by a tensile load to fracture. The main output of the experiment is fracture engineering strain. Finally, the stress-strain curves of computational models are also compared with experimental measurements.
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Elastoplastic analysis of stress and deformation and determination of fracture parameters of bodies with stress concentrators under tensile loading
Dubravec, Kristián ; Majer, Zdeněk (referee) ; Horníková, Jana (advisor)
The aim of this thesis is the construction of a diagram of fracture strain for high strength steel OCHN3MFA and its application for the estimation of fracture toughness of this material. The first part of the thesis contains the necessary theoretical framework for numerical modelling of tensile tests of various specimens - smooth specimen, specimen with a notch and specimen with a circumferential crack, it describes the influence of triaxiality on the fracture of bodies and the possibilities of construction of the diagram of fracture strain. Subsequently, a numerical model of these specimens is created using the finite element method (FEM). A non-linear, elastoplastic calculation is performed. Fracture is identified by means of comparing the true stress versus the strain obtained from tests with the finite element analysis results. Stress–strain states of specimens at the moment of fracture are obtained from a numerical model. A diagram of fracture strain is constructed, and it is used to estimate the fracture toughness of a cracked body. Finally, a local approach, which uses the diagram of fracture strain, and a classical approach of fracture mechanics, especially the stress intensity factor, are compared.
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