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Model of geometry of micro-lattice structures for finite element method
Javorský, Dominik ; Maňas, Pavel (referee) ; Červinek, Ondřej (advisor)
The growing availability of additive manufacturing technology, such as SLM, enables the creation of innovative structural designs. An example of these are complex lattice structures which are used because of their excellent mechanical properties relative to weight. One significant challenge lies in production tolerances. These are not crucial for the majority of components. However, when dealing with lattice structures and their thin-walled geometry, manufacturing tolerances lead to substantial deviations in mechanical properties. The process of designing such structures and achieving results comparable to the experiment requires the use of non-standard methods. These methods are time-consuming and costly for obtaining real geometry. The real geometry is then used for numerical simulations based on the FEM principle. This thesis focuses on the impact of geometric imperfections occurring in BCC-type structures made of stainless steel 316L. During the solution, the real geometry was obtained through optical digitization using the ATOS Triple Scan scanner. Dynamic drop-weight tests were also conducted, and the obtained results were used to modify the geometry model in combination with the acquired real geometry. The aim was to minimize the deviation between experimental and numerical simulation results below 5%. The knowledge gained from this process was then applied in simulations investigating the impact of geometric imperfections. Deviations up to 30% were observed in simulations investigating the impact of geometric imperfections. These deviations can be minimized by incorporating the knowledge of real geometry into the design. The results also help determine the diameter range within which including geometric imperfections in the design is irrelevant. Furthermore, a significant impact of the node geometry on the results of numerical simulations was observed. This knowledge brought the values closer to the experimental data. Another important contribution of this work is the simplified geometry model. This model will enable the study of the impact of additional imperfections in a range that was previously unattainable.
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Micro-lattice structures with variable strut diameter
Brulík, Karel ; Jaroš, Jan (referee) ; Červinek, Ondřej (advisor)
Due to their specific properties, micro-lattice structures have a great potential for use in energy absorption applications. It turns out that conventional micro-lattice structures with constant volume fraction can be designed for a known amount of absorbed energy. In real applications, however, we often do not know it in advance. Therefore, the use of functionally graded micro-lattice structures, which can be designed for a wider range of applied energies, appears to be more promising. The aim of this work is to compare micro-lattice structures with variable strut diameter made from 316L stainless steel by Selective Laser Melting technology in terms of energy absorption capability. For this purpose, two types of structures, F2BCC and F2BCC_45, were fabricated, both in configuration with constant, continuously variable and stepwise variable strut diameter. The structures were subsequently dynamically loaded using a drop-weight test, the results of which were described by the time history of deformation and forces. The greater amount of absorbed energy was measured for structures of type F2BCC_45, up to 73 % depending on the configuration of the structures. The results revealed that the variable strut diameter does not have a large effect on the amount of absorbed energy, but it significantly reduces the shock generated, up to 54 % depending on the type and configuration of the structure. This thesis provides a comprehensive view of the deformation and stress characteristics of both types of structures, and in particular a comparison of the effect of variable strut diameter.
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Computational Models for Non-linear Mechanical Loading Analyses of Lattice Structures Made by Laser Powder Bed Fusion
Červinek, Ondřej ; Dr. Michael R. Tucker (referee) ; Haas/, Franz (referee) ; Koutný, Daniel (advisor)
Rozvoj aditivních technologií v posledních letech umožnil výrobu meta materiálů s porézní vnitřní architekturou zvaných mikro-prutové struktury z několika typů kovových slitin. Za pomoci těchto struktur je možné vyvíjet lehké komponenty s potenciálem v oblasti absorpce mechanické energie. Jejich implementací do deformačních zón vozidel může být docíleno zvýšení bezpečnosti posádky. Vlastnosti mikro-prutových struktur umožňují navrhnout absorbéry se specifickým typem chování, které redukuje přetížení působící na posádku vozidla v případě nehody. Pro využití těchto dílů pro specifické aplikace je nutné odhadnout jejich deformační chování. Nedávný výzkum ukázal, že základový materiál těchto struktur má odlišné vlastnosti v porovnání s konvenčními objemovými komponentami vyrobenými stejnou technologií. To znamená, že pro efektivní využití mikro-prutových struktur je zapotřebí matematicky přesně popsat jejich specifické vlastnosti a deformační charakteristiky. Nicméně matematický model, který by zahrnoval popis všech významných charakteristik deformace mikro-prutových struktur, není k dispozici. Proto se tato práce zaměřuje na vývoj nelineárního numerického modelu zatěžování mikro-prutových struktur se zahrnutím efektů spojených s nejvýznamnějšími geometrickými imperfekcemi, specifickými vlastnostmi multi-prutových vzorků a dynamickými efekty. Struktury jsou vyrobeny z hliníkové slitiny AlSi10Mg a nerezové oceli 316L s využitím technologie selektivního laserového tavení. Dva odlišné přístupy jsou použity k vytvoření modelu geometrie, což umožňuje detailní inspekci deformačního charakteru. Výsledky obou modelů potvrzují, že geometrické imperfekce spojené se změnou tvaru a velikosti průřezu prutu mají významný vliv na výsledné mechanické vlastnosti. Jejich zahrnutí do modelu geometrie zvyšuje přesnost výsledků simulace. Navíc mechanické vlastnosti mikro-prutových struktur stanovené pomocí multi-prutových vzorků výrazně lépe representují vlastnosti struktur pro kvazistatické i dynamické zatěžování. Finální parametrická ověřovací simulace zatěžování mikro-prutové struktury při několika rychlostech ukazuje dobrou shodu experimentu a výpočtového řešení. Podobná parametrická studie může v budoucnu vést k nalezení efektivních strukturovaných konfigurací pro specifické množství absorbované energie bez předchozí výroby a testování.
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Design of auxetic structures for the 3D print
Sobol, Vítězslav ; Škaroupka, David (referee) ; Červinek, Ondřej (advisor)
Behavior in which the material expands in one direction and in a perpendicular direction under tensile loading is called auxetic and is associated, e. g. with increased indentation resistance. Auxetic behavior is mainly due to the typical geometry of the internal structure. Therefore, it can be achieved by a unique arrangement of inner micro-lattice structure. Through additive technologies such as Selective Laser Melting (SLM), it is possible to manufacture such complex geometry. This bachelor thesis deals with the design of a spatial micro-lattice structure that will exhibit auxetic behavior and can be made by the SLM method. Based on an extensive research on the topic of 2D and 3D auxetic structures, a new type of auxetic structure was designed. The manufacturability was verified by making several samples in different dimensional configurations. Auxeticity and mechanical properties were subsequently tested using a drop test. By evaluating it, it was possible to determine the influence of dimensional parameters on the overall behavior of the structure.
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Topology optimization of a quadcopter arm using 3D print
Simon, Jakub ; Červinek, Ondřej (referee) ; Vaverka, Ondřej (advisor)
This bachelor thesis deals with the comparison of manufacturing constraints applied during topology optimization of a demonstration component, which was a quadcopter arm. Four designed arms were optimized, each with different manufacturing constraints: Extrusion, Single draw, Split draw, Overhang and one arm only with symmetry plane, without any other manufacturing constraint. For all designs, it was important to maintain a continuous geometry during optimization and that final weight approximately equals to the weight of the original arm. All five arms were then subjected to static structural analysis with the finite element method. After that, arms were printed using Fused deposition modelling (FDM) from ABS material and then tested by static force. The photogrammetry method was used to evaluate deformation. Results of the experiment were recalculated to relative stiffness, where small differences between weights were considered. Relative stiffnesses of designed arms were then compared, showing that 4 out of 5 topology optimized arms have higher stiffness than the original shape. The toughest design is without manufacturing constraints which at the same weight has 12.5 times higher relative stiffness than the original arm.
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Design of pedal system for Pneumobil race car using topology optimisation
Pchálek, Václav ; Červinek, Ondřej (referee) ; Vaverka, Ondřej (advisor)
This thesis deals with design of pedal assembly of pneumobile racing car to increase its rigidity and reduce its weight. Based on the search, the kinematics of pedal was changed due to more precise determination of pedal ratio. Topology optimization and lattice structure were used to achieve the goals. The results were checked by strength analysis using finite element method. To produce topologically optimized parts use of metal additive technology is assumed, for which the parts have been further modified. Deformation was reduced by 13,4 % for the brake pedal and by 96,8 % for the accelerator pedal. The weight of the pedal system has been reduced by 31 %. This pedal assembly design could be an alternative to the current pedal assembly, as it is lighter and meets the requirements for higher rigidity.
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Comparison of micro-lattice structures for energy absorption
Koban, Tomáš ; Vrána, Radek (referee) ; Červinek, Ondřej (advisor)
Additively manufactured metal micro-structures have great potential in energy absorption applications. The recent research in this field led to a much better understanding of failure behaviour of these micro-structures. This thesis focuses on comparison of energy absorption ability of strut-based micro-lattice structures manufactured by selective laser melting depending on their topology and basic material. Energy absorption of three types of lattice structures (BCC, BCCZ, GBCC) made from stainless steel 316L and aluminium alloy AlSi10Mg was examined. Specific energy absorption was used to compare the two materials. The results show that micro-lattice structures made from stainless steel outperform the aluminium ones in energy absorption ability. The highest amount of absorbed energy was measured for BCCZ structure. This thesis describes the failure mechanism of micro-lattice structures and offers a complex evaluation of energy absorption for both materials.
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Design of topologically optimized upright for pneumobil race car
Mende, Milan ; Červinek, Ondřej (referee) ; Vaverka, Ondřej (advisor)
This thesis deals with the design of lightweight front uprights of pneumobile Javelin using topology optimization, followed by manufacturing by additive technology Selective Laser Melting. Aluminium alloy AlSi10Mg was used. Topology optimized parts should have met the requirement of minimal safety factor equal to 2, therefore the stress strain analysis was performed using FEM. The maximal deformation was determined and the safety factor obtained. Two unsymmetrical uprights were designed due to parameters of the brake system. The precision of manufacturing was verified by optical digitization. Machined uprights were mounted on the pneumobile and tested directly on the vehicle. No limit states were observed during testing and subsequent races, so they proved to be fully functional. Weight of the left upright was reduced from 1 609 g to 758 g, the right one was lightened to 741 g.
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Numerical model of lattice structure under dynamic loading made by Selective Laser Melting technology
Červinek, Ondřej ; Maňas, Pavel (referee) ; Vrána, Radek (advisor)
For the purpose of mechanical impact energy absorption in the transport industry are mainly used special profile absorbers. For highly specialized applications is required to use components that are designed for specific kind of deformation. Example of these parts are industrial-made metal foams or micro-lattice structures produced by SLM technology. This paper focuses on low-velocity dynamic loading prediction of BCC micro-lattice structure made of aluminum alloy AlSi10Mg by SLM technology (SLM 280HL). For this purpose dynamic FEM simulaton of the micro-lattice structure was developed, supplemented by model of BCC structure material obtained from mechanical testing. Real geometry of tested samples obtained from optical measurement (Atos Triple Scan III) was further implemented in the numerical model. Dynamic BCC structure load experiment was performed on a drop-weight tester. Behavior of structured material in drop-weight test was described by the course of deformation and reaction forces over time. Comparable results were obtained for flat loading of dynamic FEM simulation and experiment. Inclusion of production phenomena in simulation led to increased accuracy and compliance with experiment. Tool for testing the effect of geometry change on mechanical properties was created. To achieve more accurate results with puncture load, it is necessary to modify the material model with real material deformation at test sample failure.
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