|
|
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.
|
|
|
Young's Modulus on the Interface of Elastic and Elastic-Plastic Material
Kocmanová, Lenka ; Haušild, P. ; Materna, A. ; Matějíček, Jiří
The paper is aimed at determining the Young's modulus at the sharp interface between two materials, where one material is elastic and the other elastic-plastic. To determine the Young's modulus was used 3D numerical model of nanoindentation with conical indenter. The interface between the materials with the normal plane perpendicular to the direction of penetration. The goal is to simulate the combination of metal and ceramic materials.\n Young modulus according to the standardized distance from the interface are approximated inverse beta distribution and is determined by the relation between parameters inverse beta distribution of the size of the area affected by the second phase
|
|
|
FITTING OF ELASTIC MODULUS ON THE INTERFACE BETWEEN TWO MATERIALS
Kocmanová, Lenka ; Materna, A. ; Haušild, P. ; Matějíček, Jiří
The paper is aimed to determinate of Young modulus near a sharp interface. The 3D elastic numeric model was used for prediction of the Young modulus. The simulated specimen was composed of tungsten and steel. The interface was plane which a normal vector was perpendicular to the indentation force. The indenter geometry for which numerical solutions were accomplished was a rounded cone indenter. An indentation depth is studied as function of a distance indenter-interface. The distance was normalized by depth of indentation. All values of Young modulus lay on one curve after distance normalization due to elasticity. The curve was fitted by inverse beta function. The curve determine the size of area of one material influenced by a second material.
|
|
| |
guest ::
