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Anylytical solver for strength calculation of railway axles
Fišer, Petr ; Náhlík, Luboš (referee) ; Vaverka, Michal (advisor)
This master thesis deals with wheel set axles of rail vehicles, their design and methods of implementation stress analysis. In this work, I created a powered locomotive wheel set: axle and wheel. For the purpose of the design department of the Bonatrans Group a.s. company I developed an analytical solver, which allows creating stress analysis, which will be used for verifying finished design and in addition it allows printing of stress analysis as report for the railway´s offices. Next step was a stress analysis of this design of axle in this analytical solver.
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Assessment of service conditions of the screw grips of testing machine MTS 810
Votroubek, Tomáš ; Čermák, Jan (referee) ; Náhlík, Luboš (advisor)
This diploma thesis is aimed to assessment of safety of screw grips of testing machine MTS 810. Some parts of grips are predisposed to damage at low temperature (-180°C), e.g. spacer, isolating ceramics lamellas, etc. To guarantee its perfect function under hard laboratory conditions the finite element analysis was performed and suitable modifications grips parts have been suggested with respect to maximum of application of recent parts. Part of the thesis is devoted to suggestion of suitable tightening torque of experimental sample under different temperatures. For necessary numerical computations FEM system Ansys was used.
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Application of generalized linear elastic fracture mechanics on estimation of crack propagation origin from sharp V-notch
Štegnerová, Kateřina ; Máša, Bohuslav (referee) ; Náhlík, Luboš (advisor)
The master thesis is focused on estimation of crack propagation origin from sharp V-notch. Stress distribution around the tip of the V-notch is described on the base of generalized linear elastic fracture mechanics. The change of the stress singularity exponent caused by geometry of the V-notch and the vertex singularity is taken into account. The first part of the work is devoted to the estimation of the stress singularity exponent of the V-notch either from stress distribution around the tip of the V-notch or by using analytical solution. Formerly derived stability criteria are applied in the second part of the work. The origin of the crack propagation is estimated for several experimental specimens. The aim of this thesis is to compare the available experimentally observed data with results obtained using those criteria based on the application of generalized linear elastic fracture mechanics developer at the Institute of Physics of Materials Academy of Sciences of the Czech Republic. The finite element code Ansys and mathematical software Matlab were used for the necessary calculations.
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Residual fatigue life estimation of railway wheelset
Pokorný, Pavel ; Zouhar, Michal (referee) ; Náhlík, Luboš (advisor)
The first part of this master's thesis deals with the high cycle fatigue of materials, especially on growing cracks using linear elastic fracture mechanics. Much of this work is focused on the concept of stress intensity factor. This concept is nowadays one of the most widely used concepts for describing a body with crack. The first part ends with theoretical approaches to determine the residual fatigue life of the body with a crack. The second part of this master's thesis is focused on the determination of residual fatigue life of a specified railway wheelset. An existence of crack-like defect is assumed at the railway wheelset. The goal of this master's thesis is to estimate how long it will take to grow from initial defect to a critical crack length. The last part of this master's thesis is devoted to addiction order load cycles on crack growth rate.
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RESIDUAL FATIGUE LIFETIME OF RAILWAY AXLES
Pokorný, Pavel ; Fajkoš,, Rostislav (referee) ; Materna, Aleš (referee) ; Náhlík, Luboš (advisor)
This Ph.D. thesis deals with methodology for determination of residual fatigue lifetime of railway axles based on damage tolerance approach. This approach accepts an existence of potential defect, which could lead to fatigue failure of whole axle. The behavior of crack in railway axle is described by approaches of linear elastic fracture mechanics. There are plenty of factors, which more or less influence determined residual fatigue lifetime. The aim of this thesis is to quantify effects of these factors. The first part of Ph.D. thesis represents overview of studied problems relating to fatigue damage of railway axles. This part is focused on parameters, which influence fatigue crack growth in railway axle materials. The second part of thesis shows procedure for determination of residual fatigue lifetime, which was developed at the Institute of Physics of Materials of the Academy of Sciences of the Czech Republic. The main aim of this thesis was to improve current procedure for more precise estimation of residual fatigue lifetime. Significant part of this work is determination of significance of studied factors, which influencing calculated residual fatigue lifetime of railway axles (e.g. effect of threshold value, load spectrum, retardation effects, residual stress, axle geometry, material of axle etc.). The procedures described and results obtained can be also used for determination of residual fatigue lifetime of general mechanical component (not only railway axles). Therefore, results obtained in this Ph.D. thesis can be used e.g. for assessment of regular inspection intervals of cyclically loaded general mechanical parts.
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Realization of educational problem based on preloaded bolted joint apparatus
Žaba, Tomáš ; Náhlík, Luboš (referee) ; Vaverka, Michal (advisor)
In the master’s thesis an educational task concerning an experimental apparatus for quantity measurement in preloaded bolted joint is realised. In terms of its preparation an innovation of the apparatus leading to an easier and faster pretension realisation was implemented. The educational task for students and also teaching material were produced. The educational task itself consists in experimental confirmation of the relation between the tightening torque and the caused pretension. An FEM model simulating an apparatus flange deformation by given pretension was designed to verify the experiment. The thesis also contains information about the preloaded bolts, pretension elicitation methods and pretension control methods.
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Influence of a Free Surface and Gradient Change of Material Properties on a Crack Behaviour
Ševčík, Martin ; Kohout, Jan (referee) ; Klusák, Jan (referee) ; Náhlík, Luboš (advisor)
This thesis was written under the supervision of Assoc. Prof. Luboš Náhlík, Ph.D. and Assoc. Prof. Pavel Hutař, Ph.D. The topic of this thesis is the study of a free surface effect and gradient change of material properties on a crack behavior. The common theme of the work is a fracture mechanics description of a crack behavior near a material nonhomogeneity. Here, the material nonhomogeneity can be understood either as a boundary of a body (interface between body and surrounding) or as a continuous change of material properties. The thesis is introduced by a review part where the state-of-the-art of the concerned topic is described. This part presents several stress state descriptions in the vicinity of some general singular stress concentrators, particularly a crack and a V-notch. The influence of the free surface on a fatigue crack front shape is discussed here. The review part follows with the fracture mechanics description of the graded materials. The problem formulation and the main aims of the thesis are stated in the following chapter. The core of this work is the fracture mechanical description of a crack propagating near the material nonhomogeneity. The thesis focuses on a stress field description near the free surface of the body where a change in a type of the singular stress field occurs. Methods used in generalized fracture mechanics are applied here to describe the stress field near the free surface. The difference between crack behavior in thin-walled and thick-walled structures is shown and supplied by relevant examples. Methods and procedures used are later utilized for estimation of a crack behavior in graded structures. The thesis is concluded by the discussion of obtained results in appropriate context.
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Development of a New Generation of Devices with Advanced Diagnostics for Determining Contact Degradation
Dvořáček, Jiří ; Hájek, Karel (referee) ; Náhlík, Luboš (referee) ; Pazdera, Luboš (referee) ; Mazal, Pavel (advisor)
The thesis proposes a methodology for damage identification of thrust bearings using acoustic emission method. The work is the way of the hydraulic loading of specimens and thrust bearings with programmable settings severity and duration of load cycles during contact fatigue tests at stations Axmat. They are designed structural adjustment elements (waveguides) to capture the acoustic emission signal selected apparatus, including the modification of software to capture the data. At the described experiments is verified functionality of the circular test specimens and axial bearings . Part of this work is to propose a new methodology for identifying early stages of contact fatigue using a combination of diagnostic methods.
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Short fatigue crack propagation description
Trávníček, Lukáš ; Náhlík, Luboš (referee) ; Hutař, Pavel (advisor)
The presented master’s thesis deals with description of short fatigue cracks and can be divided to the several parts. In the first part, theoretical background of fatigue of materials and fracture mechanics parameters which can describe fatigue cracks is presented. Following part describes how to determine fracture mechanics parameters by finite elements method. Due to the shape of propagated fatigue crack, numerical model was established as a three-dimensional. Results obtained based on this model, was compared with literature with very good agreement. Than real shape of propagated short crack was used for description of the experimental data. It was shown, that plastic part of J-integral is suitable parameter for description of the short cracks.
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Fluid flow analysis in vicinity of exhaust valve using CFD
Šesták, Josef ; Náhlík, Luboš (referee) ; Vrbka, Martin (advisor)
This diploma thesis discuss a flow in a vicinity of exhaust valve using computational of fluid dynamics. In a light of current state of the problem solution this approach is forward but very sophisticated. Intention of author is description of multidimensional boundary of characteristic variables which determinates the flow behaviour for given geometry and boundary conditions. Technical knowlegde of fluid flow in vicinity of exhaust valve allow to design geometry which provide more effective cylinder flush out berofe the exhaust stroke will become. This process reduce quantity of loss work of piston and improve its effective pointers.
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