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DEFORMATION BEHAVIOR OF NANO/MICRO REINFORCED PMMA
Recman, Lukáš ; Nezbedová, Eva (oponent) ; Kučera, Jaroslav (oponent) ; Jančář, Josef (vedoucí práce)
The effect of particle size on magnitude of modulus and the post-yield response is highlighted. It is shown that both regions show a pronounced particle size dependence. The object of this work is to correlate a number of experimental facts and theoretical considerations regarding the mechanism of elastic and plastic deformation of amorphous polymers in general and of glassy PMMA particularly. Deformation behavior of PMMA filled with spherical particles will be observed in elastic and plastic region. The effect of particle size dependence on the modulus and strain hardening response was observed. The interpretation of reinforcing effect in nanocomposites is building up with the concept of immobilization, the nanoparticles show significant affect on the molecular dynamics and the kinetics of the disentanglement. While for the modulus measurement a large extent of data were published trying to interpret the observed trends, the strain-hardening region is somehow omitted. In an elastic region, the structure of the material maintains the same as prepared, but after passing the yield point, the primary structure is destroyed. It is shown that incorporation of the nanoparticles yields to the increase of strain hardening slope and that this slope is in a good correlation with Guth-Gold equation. It is assumed that the particles can serve as physical crosslinks yielding to physically denser entangled network.
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Development of autonomous experimental system to analyse yield surfaces distortion due to multiaxial ratcheting
Svárovský, Jiří ; Parma, Slavomír ; Štefan, Jan ; Ciocanel, C. ; Feigenbaum, H. P. ; Marek, René ; Klepač, Vilém ; Plešek, Jiří
Multiaxial ratcheting is a failure mode of structures characterized by the accumulation of plastic strain due to cyclic loading. Despite several models having been developed to predict multiaxial ratcheting, they often fail when validated with experimental data collected under a wide array of loading conditions. In this study, an experimental setup was developed and an autonomous testing procedure was used to experimentally analyze the evolution of the yield surface shape due to cyclic biaxial loading. Thin-walled tubular test specimens were made of 304L steel with a diameter of 40mm and underwent axial-torsional testing using the Instron 8852 system. The total axial strain was increased from 0 to 1% while the total shear strain underwent 5 cycles with the strain amplitude of 0.5% and the mean strain of 0.5%. Three yield surfaces were measured after the straining sequence was completed. Results showed strong directional distortional hardening and good agreement between the flow vectors and the normals to the yield surface, lending support to the associative flow rule.
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Deep learning methods for the acoustic emission methods to evaluate an onset of plastic straining
Parma, Slavomír ; Kovanda, Martin ; Chlada, Milan ; Štefan, Jan ; Kober, Jan ; Feigenbaum, H. P. ; Plešek, Jiří
Development of phenomenological plasticity models, hardening rules, and plasticity theories relies on experimental data of plastic straining. The experimental data are usually measured as the stress–strain response of the material being loaded and do not provide any clues or information about the local response of\nmaterial. In this paper, we analyze the plastic deformation of the material using the acoustic emission method and current state-of-the-art neural network models such as the InceptionTime architecture.
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Strukturně-mechanické charakteristiky vybraného typu nízkouhlíkové oceli po tažení za studena a tepelném zpracování
Stopka, Maroš ; Molliková, Eva (oponent) ; Pacal, Bohumil (vedoucí práce)
Tato bakalářská práce se zaměřuje na změny mechanických vlastností nízkouhlíkového drátu, který byl tažen za studena a následně tepelně zpracován. Mechanické zkoušky, z kterých byly změřeny hodnoty prodloužení, smluvní meze pevnosti, tažnost a počet krutů, byly provedeny na všech vzorcích do 24 hodin od jejich odebrání. Na galvanické lince byly stanoveny dvě různé rychlosti výroby, za účelem dosažení dvou různých časových intervalů žíhacího procesu. Experiment byl proveden po všech stupních redukce průměru drátu včetně vstupního materiálu. Tato práce také zahrnuje metalografické analýzy vzorků leštěných, ale také leptaných. Z těchto snímku byly následně vybrány nejvíce reprezentativní. Z výsledků vyplývá, že deformace způsobila změny v mechanických vlastnostech a zvýšení deformačního zpevnění, které bylo následně odstraněno tepelným zpracováním.
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Development of autonomous experimental setup to investigate directional distortional hardening under biaxial loading
Svárovský, Jiří ; Parma, Slavomír ; Štefan, Jan ; Ciocanel, C. ; Feigenbaum, H. P. ; Klepač, Vilém ; Marek, René ; Plešek, Jiří
Plastic deformations alter the shape of the yield surface in the stress space. Models for predicting the shape of the yield surface according to the direction of loading are being developed. Experimental data are the key factor in development and validation of phenomenological models, such as the model of directional distortional hardening cited in this study. The objective of this paper is to present the experimental setup for investigation of the directional distortional hardening. A new autonomous method was developed using an axial-torsional testing machine and the Labivew 2017 graphical programming environment to monitor the yield surface in axial stress – shear stress space. A suitable yield condition in form of effective plastic strain was used for the determination of the yield points. Initial yield surface obtained by this method shows promising agreement with von Mises model of the yield surface. Several outstanding yield points were measured which disrupt the assumption of the yield surface convexity. Therefore, possible shortcomings caused by the methodology are being investigated.
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DEFORMATION BEHAVIOR OF NANO/MICRO REINFORCED PMMA
Recman, Lukáš ; Nezbedová, Eva (oponent) ; Kučera, Jaroslav (oponent) ; Jančář, Josef (vedoucí práce)
The effect of particle size on magnitude of modulus and the post-yield response is highlighted. It is shown that both regions show a pronounced particle size dependence. The object of this work is to correlate a number of experimental facts and theoretical considerations regarding the mechanism of elastic and plastic deformation of amorphous polymers in general and of glassy PMMA particularly. Deformation behavior of PMMA filled with spherical particles will be observed in elastic and plastic region. The effect of particle size dependence on the modulus and strain hardening response was observed. The interpretation of reinforcing effect in nanocomposites is building up with the concept of immobilization, the nanoparticles show significant affect on the molecular dynamics and the kinetics of the disentanglement. While for the modulus measurement a large extent of data were published trying to interpret the observed trends, the strain-hardening region is somehow omitted. In an elastic region, the structure of the material maintains the same as prepared, but after passing the yield point, the primary structure is destroyed. It is shown that incorporation of the nanoparticles yields to the increase of strain hardening slope and that this slope is in a good correlation with Guth-Gold equation. It is assumed that the particles can serve as physical crosslinks yielding to physically denser entangled network.
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