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Influence of Plasma-nitriding on Fatigue Life of High-strength Steels under Biaxial Loading
Major, Štěpán ; Kohout, Jan (referee) ; Růžička,, Milan (referee) ; Obrtlík, Karel (referee) ; Pokluda, Jaroslav (advisor)
This work deals with fatigue life and fractographycal analysis of plasma-nitrided and virgin specimen made of the low-alloy high-strength steel. Specimens were subjected to in-phase combined bending-torsion loading. The work is focused on three groups of problems. The first group of problems was associated with the fatigue life and its prediction. The objective was to examine a relationship between the presence of the nitrided layer and fatigue life. The application of surface layers has significantly improved the fatigue life in the high-cycle region. An extended comparison between classical and advanced multiaxial criteria was performed. Criterions proposed by Marin and Matake were found to be most precise. The second objective of this work was to examine a relationship between the loading ratio ( is the bending amplitude and is the torsion amplitude ) and the fracture surface topography in the highcycle fatigue. Properties of fracture surfaces were quantified by many roughness and fractal parameters. Many roughness parameters start to incrise rapidly above a critical value of the loading ratio zc = 0,5. The last part of this work deals with the fractographical analysis of fish-eye cracks that were formed in plasma-nitrided steel specimens under symetrical bending, symetrical torsion and biaxial in-phase bending-torsion combinations.
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Influence of Plasma-nitriding on Fatigue Life of High-strength Steels under Biaxial Loading
Major, Štěpán ; Kohout, Jan (referee) ; Růžička,, Milan (referee) ; Obrtlík, Karel (referee) ; Pokluda, Jaroslav (advisor)
This work deals with fatigue life and fractographycal analysis of plasma-nitrided and virgin specimen made of the low-alloy high-strength steel. Specimens were subjected to in-phase combined bending-torsion loading. The work is focused on three groups of problems. The first group of problems was associated with the fatigue life and its prediction. The objective was to examine a relationship between the presence of the nitrided layer and fatigue life. The application of surface layers has significantly improved the fatigue life in the high-cycle region. An extended comparison between classical and advanced multiaxial criteria was performed. Criterions proposed by Marin and Matake were found to be most precise. The second objective of this work was to examine a relationship between the loading ratio ( is the bending amplitude and is the torsion amplitude ) and the fracture surface topography in the highcycle fatigue. Properties of fracture surfaces were quantified by many roughness and fractal parameters. Many roughness parameters start to incrise rapidly above a critical value of the loading ratio zc = 0,5. The last part of this work deals with the fractographical analysis of fish-eye cracks that were formed in plasma-nitrided steel specimens under symetrical bending, symetrical torsion and biaxial in-phase bending-torsion combinations.
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Mechanics of laser cut stent grafts
Major, Štěpán ; Kocour, Vladimír ; Hubálovský, Š.
This article is dedicated to a finite element analysis of tubular, laser cut stent grafts with peak-to peak bridge geometry under representative cyclic loading conditions for abdominal aortic aneurysm repair. Cardiovascular diseases are the principal cause of death in the developed world. For computational analysis, ANSYS software was employed to study the mechanical behavior of stents. Contrary to conventional engineering materials, nitinol stent fracture is not stress based but strain based. The effects of crimpling and cyclic pressure loading on stent–graft fatigue life were simulated and analyzed.
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Fatigue testing and calculation of a conical pedicle screws for spine fusion
Major, Štěpán ; Kocour, Vladimír ; Hubálovský, Š.
The main goal of spinal surgery is to stop the pain caused by joints that have worn out over time or degenerated due to disease. Spinal fusion joins together the vertebrae on either side of a joint in spine. Fixation with pedicle screws is one method which is used by surgeons for fusing the vertebrae in spine. Implants are subjected to many loading cycles during their life. Any damage to the implant leads to significant complications in the treatment and causes considerable pain. For this reason, it is necessary to pay close attention to testing and fatigue prediction of implants.
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The influence of deformation of the frame of testing device on the accuracy of Brazilian test and indirect assessment of Young modulus
Major, Štěpán ; Vavřík, Daniel ; Kocour, Vladimír ; Bryscejn, Jan
This article deals with determination of mechanical properties based on indirect measurements of brittle building materials like stones using portable device. Due to the fact, that the material samples may change their properties during transportation, it is preferred to test samples on site. For these reasons, portable testing device was developed. The testing machine operates on the split test principle. The device also shall to serve for estimation of other mechanical characteristics of the tested material, such as Young's modulus, compressive strength or flexural strength, etc. This paper concentrates on the effect of deformation of frame on the accuracy of indirect determination of mechanical properties.
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