Stiffness Analysis of Formula Student Frame

Bakalářská práce se zabývá analýzou torzní tuhosti rámu studentské formule Vector 04 týmu Formula TU Ostrava. V úvodu práce je představen projekt Formula SAE, poté následuje popis technických požadavků na vozy a jejich rámy dle pravidel Formula SAE. Práce pokračuje popisem stavby modelu pro simulaci torzní tuhosti, který je založen na tzv. metodě se dvěma nosníky, kdy rám je uchycen ke 2 nosníkům. Aplikací síly na jeden z nich je generováno zatížení rámu. Jsou popsána zjednodušení modelu a aplikovány okrajové podmínky, tak aby výsledky bylo možné porovnat s výsledky experimentu, který byl proveden ve stejném duchu pro verifikaci a nalazení simulace. Výsledky simulací a experimentu jsou porovnány mezi sebou, a také se zkrutnou tuhostí náprav. Z porovnání vyplývá, že analýza je přijatelně nalazena vzhledem k experimentu a torzní tuhost rámu vzhledem ke zkrutné tuhosti náprav je dostatečná. Nakonec jsou diskutovány možnosti optimalizace rámu z pohledu zvýšení tuhosti (popř. snížení hmotnosti) a je zde uveden příklad takové optimalizace.Bachelor thesis is dealing with analysis of torsion stiffness of the frame of Formula TU Ostrava team vehicle Vector 04. Firstly, the project Formula SAE is introduced followed by a description of technical requirements for Formula SAE vehicles and for frames of such vehicles. The thesis continues with description of simulation model for torsion stiffness analysis based on so called two-beams method. The method is based on attachment of the frame to two beams. Application of a force on one of beams causes torsion loading of the frame. Simplifications of the model are discussed and boundary conditions are applied in such manner to allow comparison of result with the experiment which is also carried out for verification and tuning of the simulation. The results from simulations and from experiment are compared together and with roll stiffness of suspension. From comparisons follows that the simulation is acceptably tuned with respect to experiment and the frame is sufficiently stiff with respect to roll stiffness of the suspension. The thesis is concluded by possibilities of optimization of the frame to increase torsion stiffness (and possibly reduce mass of the frame) and one example of such an optimization is introduced.330 - Katedra aplikované mechanikyvýborn

Stiffness Analysis of Formula Student Frame

Bakalářská práce se zabývá analýzou torzní tuhosti rámu studentské formule Vector 04 týmu Formula TU Ostrava. V úvodu práce je představen projekt Formula SAE, poté následuje popis technických požadavků na vozy a jejich rámy dle pravidel Formula SAE. Práce pokračuje popisem stavby modelu pro simulaci torzní tuhosti, který je založen na tzv. metodě se dvěma nosníky, kdy rám je uchycen ke 2 nosníkům. Aplikací síly na jeden z nich je generováno zatížení rámu. Jsou popsána zjednodušení modelu a aplikovány okrajové podmínky, tak aby výsledky bylo možné porovnat s výsledky experimentu, který byl proveden ve stejném duchu pro verifikaci a nalazení simulace. Výsledky simulací a experimentu jsou porovnány mezi sebou, a také se zkrutnou tuhostí náprav. Z porovnání vyplývá, že analýza je přijatelně nalazena vzhledem k experimentu a torzní tuhost rámu vzhledem ke zkrutné tuhosti náprav je dostatečná. Nakonec jsou diskutovány možnosti optimalizace rámu z pohledu zvýšení tuhosti (popř. snížení hmotnosti) a je zde uveden příklad takové optimalizace.Bachelor thesis is dealing with analysis of torsion stiffness of the frame of Formula TU Ostrava team vehicle Vector 04. Firstly, the project Formula SAE is introduced followed by a description of technical requirements for Formula SAE vehicles and for frames of such vehicles. The thesis continues with description of simulation model for torsion stiffness analysis based on so called two-beams method. The method is based on attachment of the frame to two beams. Application of a force on one of beams causes torsion loading of the frame. Simplifications of the model are discussed and boundary conditions are applied in such manner to allow comparison of result with the experiment which is also carried out for verification and tuning of the simulation. The results from simulations and from experiment are compared together and with roll stiffness of suspension. From comparisons follows that the simulation is acceptably tuned with respect to experiment and the frame is sufficiently stiff with respect to roll stiffness of the suspension. The thesis is concluded by possibilities of optimization of the frame to increase torsion stiffness (and possibly reduce mass of the frame) and one example of such an optimization is introduced.330 - Katedra aplikované mechanikyvýborn

Modeling of Tests on Notched Specimens Made of Stainless Steel 316L Produced by SLM Technology

Diplomová práce se zabývá modelováním zkoušek vrubovaných vzorků z nerezové oceli 316L vyrobených technologií SLM. Nejprve je uveden popis technologie SLM a teorie plasticity. Čtyři varianty vrubovaných vzorků jsou podrobeny monotónním zkouškám, a to sice tahem, krutem a kombinací tahu a krutu s využitím metody Digitální korelace obrazu. Dále je provedena výpočtová studie vrubovaných vzorků se čtyřmi materiálovými modely s pravidly zpevnění dle Chaboche a Voce a podmínkami plasticity dle von Misese a Hilla. Numerické simulace monotónních zkoušek jsou připraveny ve formě maker s parametrizovanou tvorbou geometrie. Výsledky zkoušek a numerických simulací jsou porovnány a zhodnoceny z hlediska odezvy jednotlivých materiálových modelů při víceosém stavu napjatosti. V příloze práce je uvedena rešerše tepelného zpracování a kalibrace creepových modelů, jakožto doplňující podklady pro pokračující výzkum nerezové oceli 316L vyrobené technologií SLM.Master thesis is dealing with a modeling of tests on notched specimens made of stainless steel 316L produced by SLM technology. Initially, the description of SLM technology and theory of plasticity is given. Four variants of notched specimens are put to the monotonic tests under tension, torsion, and combination of tension and torsion utilizing Digital Image Correlation system. Further, a numerical study featuring four material models considering Chaboche and Voce hardening rules and von Mises and Hill yield condition is performed. Numerical simulations are prepared in the form of macros with parametric geometry generation. The results from experiments and numerical simulations are compared and evaluated regarding the individual material model response under multiaxial stress state. Appendix of the master thesis includes a search of heat treatment and creep model calibration as additional data for further research of stainless steel 316L produced by SLM technology.330 - Katedra aplikované mechanikyvýborn

Comprehensive view on racing car upright design and manufacturing

This paper deals with the design of an upright using a topological optimization. This type of optimization is a relatively young and rapidly evolving area of computational mechanics that seeks to make multiple material savings that cannot be achieved by conventional methods. The optimized upright was utilized in a fully functional prototype of the student formula within the Formula Student competition. The main objective of the optimization was to meet the requirements of the physical properties, weight, stiffness, and strength of the upright. The initial model of the upright was iteratively optimized using topological optimization and a finite element static analysis to obtain the final model. Using the finite element analysis, its behavior in operation within individual load cases was predicted. Symmetry was used to mirror the finished model to obtain the opposite upright of the other side of the car. Finally, the topologically optimized upright was compared with an upright made by conventional methods.Web of Science126art. no. 102

On modelling of simulation model for racing car frame torsional stiffness analysis

This paper concerns the modelling of the simulation structure for the torsional stiffness evaluation of a Formula SAE vehicle frame and presents some insights into the modelling of the problem using a beam-like model together with geometrical simplifications. The insights consist of presenting utilized simplifications and assessing their influence on torsional stiffness. The simulation model, consisting of the vehicle frame, suspension and testing fixture of complex shapes, requires certain simplifications to achieve a sustainable modelling and computational time while getting reasonable results. The influence of simplifications such as a linear isotropic material model for carbon-fibre and geometrical simplifications of the suspension, frame and testing fixture are discussed. The simulation model was developed in such a way to allow the easy change of cross-sections and geometry during the vehicle design process. The simulation model was also experimentally validated. A comparison of the results from the simulation and testing showed an acceptable difference (up to 10%), thus a small influence of the material and geometrical simplifications on the results of torsional stiffness is considered.Web of Science5965133512

On aluminum honeycomb impact attenuator designs for Formula Student competitions

The use of impact attenuators (IA) is important for vehicles as they absorb the kinetic energy exerted from the car crashes to protect the drivers from any possible injuries. Under the framework of the Formula Student (FS) competition, we investigate various designs of IA made of aluminum honeycomb material. Specifically, the crushing behavior of the honeycomb structure is investigated from the theoretical point of view and later verified with numerical simulations. To achieve the desired crushing behavior of the aluminum honeycomb structure, apart from the so-called pre-crushing method, another way to pre-process the aluminum honeycomb is proposed. Modification on the aluminum honeycomb is done in a symmetric manner to ensure the same uniform crushing behavior on the two sides of the mirror plane of the car. Different variations presented in this paper shed a light on future aluminum honeycomb IA designs in the context of FS competitions.Web of Science1210art. no. 164

Monotonic tension-torsion experiments and FE modeling on notched specimens produced by SLM technology from SS316L

The aim of this work was to monitor the mechanical behavior of 316L stainless steel produced by 3D printing in the vertical direction. The material was tested in the "as printed" state. Digital Image Correlation measurements were used for 4 types of notched specimens. The behavior of these specimens under monotonic loading was investigated in two loading paths: tension and torsion. Based on the experimental data, two yield criteria were used in the finite element analyses. Von Mises criterion and Hill criterion were applied, together with the nonlinear isotropic hardening rule of Voce. Subsequently, the load-deformation responses of simulations and experiments were compared. Results of the Hill criterion show better correlation with experimental data. The numerical study shows that taking into account the difference in yield stress in the horizontal direction of printing plays a crucial role for modeling of notched geometries loaded in the vertical direction of printing. Ductility of 3D printed specimens in the "as printed" state is also compared with 3D printed machined specimens and specimens produced by conventional methods. "As printed" specimens have 2/3 lower ductility than specimens produced by a conventional production method. Machining of "as printed" specimens does not affect the yield stress, but a significant reduction of ductility was observed due to microcracks arising from the pores as a microscopic surface study showed.Web of Science141art. no. 3

3D printed hollow off-axis profiles based on carbon fiber-reinforced polymers: Mechanical testing and finite element method analysis

The aim of the paper is to design, manufacture, and test an off-axis composite profile of circular cross-section. Composite profile based on continuous carbon fibers reinforcing the onyx matrix, i.e., a matrix that consists of nylon and micro carbon fibers, was produced by fused deposition modeling (FDM) method. A buckling test of the six printed composite specimens was performed on a tensile test machine. The values of the experiment were compared with the values of the computational simulation using the Finite Element Method (FEM) analysis. The mean value of the experimentally determined critical force at which the composite profile failed was 3102 N, while the value of the critical force by FEM analysis was calculated to be 2879 N. Thus, reliability of the simulation to determine the critical force differed from the experimental procedure by only 7%. FEM analysis revealed that the primary failure of 3D printed composite parts was not due to loss of stability, but due to material failure. With great accuracy, the results of the comparison show that it is possible to predict the mechanical properties of 3D printed composite laminates on the basis of a theoretical model.Web of Science1317art. no. 294

Failure of thymic deletion and instability of autoreactive Tregs drive autoimmunity in immune-privileged liver

The liver is an immune-privileged organ that can deactivate autoreactive T cells. Yet in autoimmune hepatitis (AIH), autoreactive T cells can defy hepatic control and attack the liver. To elucidate how tolerance to self-antigens is lost during AIH pathogenesis, we generated a spontaneous mouse model of AIH, based on recognition of an MHC class II–restricted model peptide in hepatocytes by autoreactive CD4+ T cells. We found that the hepatic peptide was not expressed in the thymus, leading to deficient thymic deletion and resulting in peripheral abundance of autoreactive CD4+ T cells. In the liver, autoreactive CD4+ effector T cells accumulated within portal ectopic lymphoid structures and maturated toward pathogenic IFN-γ and TNF coproducing cells. Expansion and pathogenic maturation of autoreactive effector T cells was enabled by a selective increase of plasticity and instability of autoantigen-specific Tregs but not of nonspecific Tregs. Indeed, antigen-specific Tregs were reduced in frequency and manifested increased IL-17 production, reduced epigenetic demethylation, and reduced expression of Foxp3. As a consequence, autoantigen-specific Tregs had a reduced suppressive capacity, as compared with that of nonspecific Tregs. In conclusion, loss of tolerance and the pathogenesis of AIH were enabled by combined failure of thymic deletion and peripheral regulation