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Description of the residual stresses in polymer pipes
Poduška, Jan ; Majer, Zdeněk (referee) ; Hutař, Pavel (advisor)
This thesis is dealing with the issue of residual stress present in the wall of a polymer pipe and the influence on its lifetime. Experimental data obtained by the ring slitting method are evaluated and the tangential residual stress in the wall of polypropylene pipe is determined. The evaluation is carried out using a new methodology based on the curved beam theory. The method is verified using numerical simulation. 3D numerical model is used to verify the behavior of the pipe, when there are both tangential and axial residual stresses present in the pipe wall, because the presence of axial stress causes a rise in the magnitude of tangential residual stress. A correction of the tangential stress values corresponding to the pipe length is then proposed. It is shown, that the distribution of the tangential residual stress does not depend significantly on the dimensions or ma-terial of the extruded pipe and a general equation is proposed to describe the distribution. This general distribution is then involved in the calculations of the pipe lifetime that are carried out using a method based on the linear elastic fracture mechanics. A significantly lower lifetimes are obtained when taking the residual stress into account.
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Prediction of slow crack growth in polymer pressure pipes
Luky, Robin ; Knésl, Zdeněk (referee) ; Hutař, Pavel (advisor)
A new methodology of polymer pipe lifetime estimation taking into account residual stresses is described in this thesis. Engineering equations derived based on numerical simulations of a hydrostatic pressure test are proposed. Residual lifetime calculations were performed for different loading conditions using experimental data of a creep crack propagation in studied material and stress distribution in the pipe wall. The effects which significantly influence lifetime estimation were quantified with special focus on residual stresses.
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Computational analysis of leveling of square cross section rods
Šebek, František ; Návrat, Tomáš (referee) ; Petruška, Jindřich (advisor)
Current requirements in mechanical engineering require more accurate operations and more efficient technologies. The aim of this thesis is the analysis of the leveling of square rods. The main problem is the setting of the leveling machine for the specified material and geometric data so that the initially curved material, which passes through alternatively positioned offset rollers, is leveled as much as possible. The main factor in the leveling process is the plastification of the material used for the redistribution of the residual stress. Based on existing theo-retical knowledge in this field, programs are set up to simulate the passing of the rod through the leveling machine. Further, modifications leading to the improvement of the whole process are presented. Finally, there is a verification of the results which is made independently of the submitted solution and processed by the finite element method.
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Material nonlinear static response of civil structures
Kinclová, Radka ; Vlk, Zbyněk (referee) ; Nevařil, Aleš (advisor)
The aim of this bachelor’s thesis is the non-linear elastic and plastic response of the simple beam structures. Also the problematics of the plastic hinges development is adressed. This thesis will then describe the origin and magnitude of the residual stresses caused by welding. Ideal elastic-plastic behavior of materials and elastic behavior with strenghtening will be used to determine the limit load capacity of the simple structures and will be compared to solution in the ANSYS software.
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Description of Crack Propagation in the Fields of Strongly Non-Homogeneous and Residual Stresses
Štegnerová, Kateřina ; Materna, Aleš (referee) ; Malíková, Lucie (referee) ; Náhlík, Luboš (advisor)
This Ph.D. thesis was written under the supervision of Assoc. Prof. Luboš Náhlík, Ph.D. and Assoc. Prof. Pavel Hutař, Ph.D. Thesis is focused mainly on application of generalized linear elastic fracture mechanics, which allows description of crack behaviour propagating from general singular stress concentrators, such as material interfaces or sharp V-notches, and verification of validity of used fracture criteria. The obtained results were used in the next part of the thesis, which deals with the issue of crack propagating in ceramic composites, where the stress distribution field is strongly influenced by the existence of material interface and presence of residual stresses, that arise during manufacturing process of composite.
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Strengthening of axially loaded steel members under load
Vild, Martin ; Wald,, František (referee) ; Křivý,, Vít (referee) ; Bajer, Miroslav (advisor)
Dissertation focuses on strengthening of axially loaded steel members strengthened under load. Strengthening under load using welding is time and financially efficient. Plastic design can be used for members without stability problems. However, the design of members susceptible to buckling is difficult and opinions of researchers differ on this matter and there are only several experiments. The dissertation is focused on strengthening under load of members with selected cross-sections susceptible to flexural buckling. It is necessary to check the resistance of the base member weakened by the elevated temperatures caused by welding. The preload and welding – residual stress and deformations – must be taken into account for the determination of the buckling resistance of the member strengthened under load. The aim of this dissertation is to provide the load resistance of selected compressed members strengthened under load. Author performed experiments on members with the H and L shaped cross-sections and seamless tubes. Other experiments were performed on members with H shaped cross-section and rectangular hollow sections to determine the resistance of base member during welding. These served to validate numerical models which helped to increase the number of specimens for statistical evaluation. Analytical models to determine the load resistances of the base member during welding and the strengthened member were developed using experiments from literature and author’s experiments and numerical models. The simplified model is conservative and suitable for practical design. The complex model is suitable for scientific purpose and it provides both deformation and load resistance using modified imperfection factor. It provides a good agreement with the experiments. Doctoral thesis also includes practical recommendations for design and execution of strengthening under load using welding.
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Description of Crack Propagation in the Fields of Strongly Non-Homogeneous and Residual Stresses
Štegnerová, Kateřina ; Materna, Aleš (referee) ; Malíková, Lucie (referee) ; Náhlík, Luboš (advisor)
This Ph.D. thesis was written under the supervision of Assoc. Prof. Luboš Náhlík, Ph.D. and Assoc. Prof. Pavel Hutař, Ph.D. Thesis is focused mainly on application of generalized linear elastic fracture mechanics, which allows description of crack behaviour propagating from general singular stress concentrators, such as material interfaces or sharp V-notches, and verification of validity of used fracture criteria. The obtained results were used in the next part of the thesis, which deals with the issue of crack propagating in ceramic composites, where the stress distribution field is strongly influenced by the existence of material interface and presence of residual stresses, that arise during manufacturing process of composite.
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Strengthening of axially loaded steel members under load
Vild, Martin ; Wald,, František (referee) ; Křivý,, Vít (referee) ; Bajer, Miroslav (advisor)
Dissertation focuses on strengthening of axially loaded steel members strengthened under load. Strengthening under load using welding is time and financially efficient. Plastic design can be used for members without stability problems. However, the design of members susceptible to buckling is difficult and opinions of researchers differ on this matter and there are only several experiments. The dissertation is focused on strengthening under load of members with selected cross-sections susceptible to flexural buckling. It is necessary to check the resistance of the base member weakened by the elevated temperatures caused by welding. The preload and welding – residual stress and deformations – must be taken into account for the determination of the buckling resistance of the member strengthened under load. The aim of this dissertation is to provide the load resistance of selected compressed members strengthened under load. Author performed experiments on members with the H and L shaped cross-sections and seamless tubes. Other experiments were performed on members with H shaped cross-section and rectangular hollow sections to determine the resistance of base member during welding. These served to validate numerical models which helped to increase the number of specimens for statistical evaluation. Analytical models to determine the load resistances of the base member during welding and the strengthened member were developed using experiments from literature and author’s experiments and numerical models. The simplified model is conservative and suitable for practical design. The complex model is suitable for scientific purpose and it provides both deformation and load resistance using modified imperfection factor. It provides a good agreement with the experiments. Doctoral thesis also includes practical recommendations for design and execution of strengthening under load using welding.
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Description of the residual stresses in polymer pipes
Poduška, Jan ; Majer, Zdeněk (referee) ; Hutař, Pavel (advisor)
This thesis is dealing with the issue of residual stress present in the wall of a polymer pipe and the influence on its lifetime. Experimental data obtained by the ring slitting method are evaluated and the tangential residual stress in the wall of polypropylene pipe is determined. The evaluation is carried out using a new methodology based on the curved beam theory. The method is verified using numerical simulation. 3D numerical model is used to verify the behavior of the pipe, when there are both tangential and axial residual stresses present in the pipe wall, because the presence of axial stress causes a rise in the magnitude of tangential residual stress. A correction of the tangential stress values corresponding to the pipe length is then proposed. It is shown, that the distribution of the tangential residual stress does not depend significantly on the dimensions or ma-terial of the extruded pipe and a general equation is proposed to describe the distribution. This general distribution is then involved in the calculations of the pipe lifetime that are carried out using a method based on the linear elastic fracture mechanics. A significantly lower lifetimes are obtained when taking the residual stress into account.
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