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Interaction of pulsating water jet with surface of structural materials
Poloprudský, Jakub ; Müller,, Miroslav (oponent) ; Chlup, Zdeněk (oponent) ; Kruml, Tomáš (vedoucí práce)
The pulsating water jet (PWJ) is a hybrid technological modification of the continuous water jet (CWJ) working at the principle of impact pressure. PWJ is created by splitting the coherent stream of water into discrete clusters. The clusters create the so-called water hammer effect, which significantly increases the effectivity of erosion of the material subjected to PWJ. This work deals with the interaction of water clusters created by the PWJ with the surface of selected structural materials. The work focuses on the incubation erosion stage before the start of the material removal. The experimental materials used were austenitic 316L stainless steel and aluminium alloy AW-2014, due to their excellent corrosion resistance in tap water environment and their homogeneity and low hardness respectively. Both of these materials are according to literature review common for waterjet focused research. The PWJ is a novel technology with several technological parameters, which offers the potential for technology optimization and opens questions about its possibilities and limitations. The individual clusters of water are expected to act upon the surface in a similar way as liquid droplets. Under this approximation, the technology is currently a candidate for use as an erosion testing tool. The advantages of PWJ erosion testing compared to conventional erosion testing tools are the high frequency of impacts and control over the impact speed, droplet size, angle of droplet impacts and impact frequency. The work focuses on the incubation erosion stage, which is the stage prior to macroscopic material removal. The incubation stages consist of plastic deformation of the material, surface deformation exposing the grain boundaries and the creation of surface steps. The goal is to tune the use of PWJ technology for erosion testing, surface roughening and surface strengthening. The main findings are as follows: • 316L stainless steel and AW-2014 were treated with PWJ moving along a linear trajectory with different levels of pressure and cluster impact distribution. The influence of cluster impact distribution on the erosion stage was evaluated. • The static PWJ with increasing erosion time was done on 316L steel. The subsurface changes corresponding with surface changes were documented using transmission electron microscopy. A new erosion stage was proposed between material roughening and macroscopic material removal stages. This stage precedes the formation of micropits and is defined by the presence of cracks at preferential sites. • The surface hardening of 316L steel was measured on cross-sections after PWJ treatment. Hardening up to depth of 100 µm was observed before significant material removal started. • A substantial increase of the fatigue life of 316L steel specimen after treatment by PWJ was found. This is a quite interesting and original finding, opening the possibility of developing a new way for surface engineering. The dependence between PWJ the feed rate and a number of cycles to failure was measured for two strain levels within the experimental design. • Electron back scattered diffraction measurement was done before and after PWJ treatment. Changes in grain orientation were measured and kernel average misorientation was evaluated. The proposal of this new methodology for erosion incubation stage observation is the highlight of this work.
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Simulace válečkování pomocí explicitní MKP
Bezrouková, Martina ; Zemčík, Oskar (oponent) ; Zouhar, Jan (vedoucí práce)
Cílem práce je uvedení do problematiky explicitních metod MKP a seznámení s komerčními programy, ve kterých je možné provádět simulace. V další části jsou specifikovány technologické podmínky a oblasti použití válečkování. Součástí této práce bylo vytvoření modelu pro simulaci válečkování. Výpočty byly provedeny v programu ANSYS LS-DYNA. V závěru jsou prezentovány výsledky simulace a technicko-ekonomický přínos metody válečkování.
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Simulace válečkování pomocí explicitní MKP
Bezrouková, Martina ; Zemčík, Oskar (oponent) ; Zouhar, Jan (vedoucí práce)
Cílem práce je uvedení do problematiky explicitních metod MKP a seznámení s komerčními programy, ve kterých je možné provádět simulace. V další části jsou specifikovány technologické podmínky a oblasti použití válečkování. Součástí této práce bylo vytvoření modelu pro simulaci válečkování. Výpočty byly provedeny v programu ANSYS LS-DYNA. V závěru jsou prezentovány výsledky simulace a technicko-ekonomický přínos metody válečkování.
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