Articles (RTI)

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Showing 1 - 20 out of 121 results

Equations of Motion of Mechanical Systems with Switchable Constraints
(2024) Kovanda, Jan; Hozman, Jiří
The article deals with a numerical and analytical approach to solvingthe equations of motion, which enables to treat the considered problems with thechange of system structure or number of degrees of freedom without interruptingthe numerical integration process. The described methodology allows effectivelyincorporate switchable constraints in the systems in accordance with their flexiblestructures. The crucial idea is based on the formulation of the resulting differential-algebraic equations into a saddle point system, where the switchable constraintsare represented by a sign matrix with variable rank. In connection with this prop-erty, a pseudoinversion is applied to eliminate algebraic variables and transform theproblem to the first order system of ordinary differential equations. Moreover, thetime independent case leads to linear autonomous systems with non-diagonalizablematrices, as is proved. The relevant numerical scheme is based on Runge-Kuttamethods, that correspond to the power series of the resulting matrix exponen-tial for time independent problems. The methodology presented is illustrated onthe idealized two-mass oscillator with a switchable constraint. The numerical ex-periments performed range from initial stages, through simple transient cases todamped intentional control. The advanced applications can be found in robotics,active and controlled systems, and in the simulations of complex systems in biologyand related areas. Moreover, the methodology can also be applied in the simula-tion of transport systems, especially in relation to vehicle technology, a quarter carsuspension system, a vibration control mechanism, a torsion system with a clutch,and machine balancing and storage should to be highlighted.
Fatigue evaluation of bus welded joints under realistic loading: a dual-criterion approach
(2025) Zanichelli, Andrea; Kepka, Miloslav; Kepka, Miloslav; Ronchei, Camilla; Scorza, Daniela; Vantadori, Sabrina
Fatigue failures in vehicles and their structural parts due to random loading represent a major concern in product development, particularly during the design phase. In this context, the aim of the present study is twofold. First, it seeks to optimise the fatigue life of a specific case study - namely, a welded joint in the thin-walled profiles of a bus bodywork - by evaluating three different geometric variants of the joint. This optimisation is carried out using a time-domain random fatigue criterion. The analysis begins with experimental service stress-time histories recorded at the critical location of the bus bodywork, corresponding to two distinct travelled road types and two loading conditions. These data are used in the time-domain fatigue analysis to identify the most suitable welded joint variant capable of meeting the required service fatigue life. Once the optimal joint configuration – identified as variant 1 - is selected, both time-domain and frequency-domain fatigue criteria are applied to predict the fatigue life. This second phase considers four additional service stress-time histories obtained from two specialtesting tracks, under both empty and fully bus loading conditions, in order to evaluate the consistency and reliability of the two fatigue assessment approaches.
On Occupant Identification and Related Crash Outcome in Out of Position Conditions
(2025) Vergnano, Alberto; Kovanda, Jan
The methodology for crash tests in vehicle development and homologation is based on dummies sitting in a standardized posture, defined by the H-point of the car body and design specifications. As a result, injury criteria are directly influenced by these precisely defined initial conditions. Out-of-Position scenarios are not included in passive safety tests but are usually analysed conventionally through specialized experiments. The combination of crash dynamics and improper airbag deployment can increase the forces exerted on the body. While airbags have saved numerous lives, statistics also report injuries and fatalities caused by improper contact with deploying airbags. This study examines strategies to make the Airbag Control Unit effectively adaptive to an occupant position. Pre-crash scenarios are identified using sensors in the vehicle seat and the corresponding outcomes are simulated. The research highlights the importance of a thorough examination of crash circumstances, process and outcomes to improve safety in intelligent vehicles.
Monitoring Occupant Posture Using a Standardized Sensor Interface with a Vehicle Seat
(2025) Vergnano, Alberto; Pelizzari, Alessandro; Giorgianni, Claudio; Kovanda, Jan; Zimmer, Alessandro; Lopes da Silva, Joed; Rezvanpour, Hamed; Leali, Francesco
Car safety can be enhanced by enabling the Airbag Control Unit (ACU) to adaptively deploy different charges based on the occupant’s position once the crash occurs. In this context, monitoring the occupant’s position using a sensorized seat integrated with an Inertial Measurement Unit (IMU) offers a practical and cost-effective solution. However, certain challenges still need to be addressed. The adoption of sensorized seats in research and vehicle set-up is still under consideration. This study investigates an interface device that can be reconfigured to suit almost any seat model. This reconfigurability makes it easily adaptable to new vehicles under development and applicable to any passenger seat in the vehicle. This paper details the device’s design, including its programming using calibration and monitoring features, which significantly improves its reliability compared to earlier prototypes. Extensive testing through real driving experiments with multiple participants demonstrated an accuracy range of 45–100%. The testing involved both drivers and passengers, showcasing the device’s ability to effectively monitor various in-car scenarios.
Extending the fatigue performance of new and repaired welded T-specimens using High Frequency Mechanical Impact
(2025) Kepka, Miloslav; Kepka, Miloslav
In this study, an experimental investigation was conducted to evaluate the benefit of high-frequency mechanical impact (HFMI) on both newly welded and repaired steel joints. Welded specimens in the as-welded condition, identical specimens treated with HFMI, and HFMI-treated repaired welds were subjected to constant-amplitude cyclic loading until failure. The testing involved structural steel joints representative of typical bridge and shipbuilding details. HFMI treatment was applied along the weld toes using a standard pneumatic impact tool, and all specimens were tested under controlled laboratory conditions to record S–N (stress–life) data. HFMI-treated specimens, including both new and repaired welds, exhibited significantly improved fatigue resistance compared to their as-welded counterparts. Specifically, the HFMI-treated welds endured 2–3 times longer life than as-welded joints under equivalent loading. Additionally, the application of HFMI to repaired welds further extended their fatigue life, demonstrating that HFMI is not only effective in new structures but also offers substantial benefits for welded-joint rehabilitation. The treated joints showed a notable increase in fatigue life and an improvement in the FAT class (allowable stress range at 2 × 10⁶ cycles)
Changes in Mechanical Properties of Medium Manganese Steel After Forming, Press Hardening, and Heat Treatment
(2025) Leták, Radek; Kučerová, Ludmila; Jirková, Hana; Jeníček, Štěpán; Votava, Filip
Medium manganese steels fall into the category of modern third-generation high-strength steels. Thanks to their alloying, they use a number of strengthening mechanisms, such as the TRIP and TWIP effects, to achieve their mechanical properties. The excellent combination of strength and ductility also makes them suitable for safety components in car shells, such as side reinforcements. Medium manganese steel with 0.2% C, 5% Mn, and 3% Al was used for the experimental program. Sheets with a thickness of 1.8 mm without surface treatment were formed in a press hardening tool. Side reinforcements require various mechanical properties in different parts. The change in mechanical properties was tested on the produced profiles. The changes in the tested regions were produced by local heating to an intercritical region. These results were compared with classically annealed specimens in a furnace. In the case of tool hardening, strength limits were over 1450 MPa with a ductility of about 15%.
Parametric Production of Prostheses Using the Additive Polymer Manufacturing Technology Multi Jet Fusion
(2024) Ráž, Karel; Chval, Zdeněk; Kemka, Vladislav
This study aims to develop a procedure for the production of 3D-printed forearm prostheses (especially hard outer sockets). The production procedure is designed in the form of a parametric workflow (CAD model), which significantly speeds up the designing process of the prosthesis. This procedure is not fixedly dependent on the software (SW) equipment and is fully transferable into another SW environment. The use of these prostheses will significantly increase the comfort of their patients' lives. It is possible to produce prostheses faster and in larger amounts and variants by the usage of additive technology. The input for the own production of the prosthesis is a model of the internal soft socket of the patient. This soft socket (soft bed) is made by a qualified prosthetist. A 3D-scanned CAD model is obtained afterward using the scanning method by an automatic laser projector. An editable, parametric external socket (modifiable in any CAD format) is generated from the obtained 3D scan using a special algorithmic model. This socket, after the necessary individual modifications, is transferred to 3D printing technology and produced using powder technology Multi Jet Fusion (HP MJF). The result of the designed and tested procedure is a quickly editable 3D-printed outer socket (main part of prosthesis), which is able to fully replace the current long-fiber composite solution. Production of current solutions is relatively time-consuming, and only one piece is produced in a given time. The newly designed technology eliminates this. This study summarized the possibilities of speeding up the production of forearm prostheses (but not only these) by creating a parametric CAD model that is applicable to different patients.
Effects of Heat Treatment on Additively Manufactured 316L Stainless Steel
(2022) Burdová, Karolína; Jirková, Hana; Kučerová, Ludmila; Zetková, Ivana; Mach, Josef
The microstructure and mechanical properties of selectively laser melting (SLM)-manufactured 316L stainlesssteele were evaluated by scanning electron microscopy, tensile testing at ambient temperature andCharpy impact test. These samples were compared with as-built samples. Following heat treatment conditionswere used: 500 °C for 2/4 hours, 650 °C for 2 hours and 900 °C for 1 hour. Cooling took place infurnace and in furnace with opened valve. Compared to as built samples the heat treatment at lowertemperature negatively influenced elongation but increased the amount of energy absorbed by materialduring fracture.
A case study on fatigue life assessment of an electric bus bodywork
(2024) Kepka, Miloslav; Kepka, Miloslav; Minich, Radovan
Bus bodywork requires a thorough assessment of strength and fatigue life. The rise of battery-powered electric buses in the market brings new challenges due to the weight of the battery containers affecting the dynamic characteristics of the vehicle and the stress on its bodywork and chassis frame. When a manufacturer decides to develop a conceptually new vehicle, it does not initially have the precise input information necessary to assess the strength and fatigue life of the vehicle body. In particular, information about the future operating loads must be more or less estimated at the design stage of the structure and refinement is possible only after measurements with a vehicle prototype. This paper focuses on the fatigue life evaluation of the bodywork of a new articulated electric (battery) bus. The results are confronted with previous experience from the development and testing of the bodyworks of diesel buses and trolleybuses. Experimentally determined and statistically evaluated S-N curves of structural nodes welded from thin-walled profiles and measured stress spectra were used to estimate the fatigue life using the hypotheses of accumulation of fatigue damage. The findings resulted in recommendations to improve the operational reliability of a particular vehicle and provided challenges for future research. However, it should be noted that some of the findings and conclusions presented in this paper relate exclusively to the bodyworks of urban public transport vehicles and not to long-distance passenger transport vehicles
Influence of Higher Stabilization Temperatures on the Microstructure and Mechanical Properties of Austenitic Stainless Steel 08Ch18N10T
(2023) Janda, Tomáš; Jeníček, Štěpán; Kučerová, Ludmila; Leták, Radek; Jandová, Dagmar; Jirková, Hana
Precipitation strengthening in titanium-stabilized austenitic stainless steels can improve the hot yield strength, as requested, e.g., for nuclear industry applications. The resulting properties depend mainly on the parameters of the heat treatment and previous forming. The influence of the heat treatment parameters on the development of the microstructure and mechanical properties was determined for steel 08Ch18N10T (GOST). Solution annealing and stabilization with different temperatures and holds were performed on the steel, which was, in delivered condition, stabilized at 720 °C. Heat-treated samples were subjected to static tensile testing at room temperature and at 350 °C, microstructural analysis using light, scanning electron and transmission electron microscopy focused on precipitates, and HV10 hardness testing. The strengthening mechanism and its dependence on the stabilization parameters are described. The results of the experiment show the influence of the state of the input material on the final effect of heat treatment—repeated heat treatment achieved lower-strength characteristics than the initial state, while almost all modes showed above-limit values for the mechanical properties. Stabilization temperatures of 720 to 800 °C were found to be optimal in terms of the achieved hot yield strength. At higher temperatures, slightly lower strengths were achieved, but at significantly shorter dwell times.
Analysis of Static and Cyclic Properties of 316L and AlSi10Mg in Conventional Casting and Additive Manufacturing
(2024) Chmelko, Vladimír; Margetin, Matúš; Zetková, Ivana; Norek, Martin; Likavčan, Filip
The paper presents the original results of cyclic testing of materials that are identical in chemical composition but produced by two different technologies: conventional metallurgy and additive manufacturing. For the aluminium alloy AlSi10Mg and the austenitic steel 316L, tensile curves, tension–compression and torsion alternating fatigue curves are experimentally obtained and presented. The experimental results are compared for two fabrication technologies—conventional metallurgy and additive DLMS technology. The results indicate a significant effect of anisotropy on the fatigue performance of the AM materials and a different slope of the fatigue life curves in the cyclic torsion versus cyclic tension–compression. The static and, in particular, the fatigue properties of both materials are discussed in relation to the microstructure of the materials after conventional production and after additive manufacturing. This comparison allowed us to explain both the causes of the anisotropy of the AM materials and the different slope of the curves for normal and shear stresses under cyclic loading. Using the example of the strength assessment of bicycle frames, the possibility of progressively wider use of additive manufacturing for load-bearing structures is presented.
Determination of Mechanical Properties of Blind Rivet Joints Using Numerical Simulations and Experimental Testing
(2025) Beber, Martin; Stejskal, Martin; Sedláček, František
This study explores the tensile performance of blind rivet joints in galvanized steel sheets, focusing on their behavior under shear and normal load conditions. Blind rivets are frequently used in structural applications due to their ease of installation and ability to be applied from one side, making them highly effective in industries like aerospace and automotive. Two types of DIN 7337—4.8 × 8 blind rivets—galvanized steel St/St and stainless steel A2/A2—paired with galvanized steel sheets DX51D + Z275, were experimentally tested to assess how their material properties affect their joint strength, deformation patterns, and failure modes. Single-lap shear, double-lap shear, and pure normal load tests were conducted in multiple configurations to evaluate joint performance under varying loading conditions, simulating real-world stresses. Using custom-built equipment, controlled forces were applied perpendicular to the rivet joints to replicate practical loading conditions. The results revealed distinct differences in the load-bearing capacities of the two materials, offering valuable insights for applications where corrosion resistance and structural integrity are critical. Finite element analysis (FEA) was then used to simulate the behavior of the joints, with the results validated against experimental data. To enhance the reliability of numerical simulations in optimizing the design of rivet joints, a methodology was proposed to calibrate non-linear FEA models to experimental results, and a substantial agreement of 92.53% was achieved via optimization in ANSYS OptiSLang. This research contributes to our broader understanding of riveted connections, providing practical recommendations for assessing the performance of such joints in various engineering fields.
Low-temperature precipitation strengthening of maraging steel 1.2709 produced by powder bed fusion
(2024) Kučerová, Ludmila; Benediktová, Anna; Burdová, Karolína; Jandová, Dagmar
Research into precipitation hardening in additively manufactured (AM) maraging steel is mainly conducted on the material after several hours of holding at the peak hardening temperatures of 450-500 °C. Lower temperatures are expected to have little to no effect on mechanical properties even after very long holds at these temperatures. This article, however, demonstrates that new precipitates grow and cause a noticeable hardening effect in solution-annealed AM maraging steel after only a 6-hour hold at a temperature of 350 °C. High-resolution scanning and transmission electron microscopy (HRSEM, HRTEM) was used to identify the new precipitates. Very fine coherent microdomains containing mainly nickel and molybdenum layers were found. Particles of a new phase, Al0.5CNi3Ti0.5, were also detected. Additionally, various precipitates were also found in both the as-built and the AM solution-annealed maraging steel samples. Precipitates such as Ni3Ti, Al0.3Ni0.35Ti0.35 and Al2O5Ti, were also observed in the as-built condition. After subsequent solution annealing at 820 °C additional Ni3Mo particles and another type of Ti-rich particles, Ni4Ti3, were further found in the AM steel microstructure. The additional new phases which precipitated during the final hardening at 350 °C caused an 18% (200 MPa) increase in strength.
Minimizing Deformations during HP MJF 3D Printing
(2023) Ráž, Karel; Chval, Zdeněk; Thomann, Sacha
(1) Background: The purpose of this study is to investigate deformations that occur during additive manufacturing by the HP (Hewlett-Packard) Multi Jet Fusion (MJF) process. These deformations are affecting final properties of 3D printed parts and proper compensating technology has to be developed in order to minimize these deformations.; (2) Methods: Parts were printed with powder composed of nylon plastic infused with glass beads (PA12GB). The technology HP MJF was used during investigation. All parts (specimens) were measured at different points over an extended period to follow the deformations at each point. Different finite element simulations were performed to compare them with real results and assess the viability of using simulations to save time. Various modules for the DIGIMAT software such as Additive Manufacturing (AM), Material-Focused (MF), Finite Element (FE), and Computer- Aided Engineering (CAE) were used to run the simulations.; (3) Results: It is shown that the printing position of the part in the printer has an impact on deformations. When the part is simulated in the tilted position but alone (deformation 7.19 mm), the value of the deformation is 1.49 mm greater than when the other parts (two comparable parts) are simulated at the same time (deformation 5.7 mm). The difference between the simulation with the three parts together (deformation 5.7 mm) and reality (deformation 3.44 mm) is 2.26 mm. Finally, the difference between the simulated single part (deformation 7.19 mm) and the real part (deformation 3.44) is 3.75 mm.; (4) Conclusions: The results of this study will contribute to a better understanding of deformation mechanisms and will suggest solutions for improving the quality of printed parts. 3D printing is a rapidly growing technology that offers numerous possibilities across various fields. However, one commonly encountered issue is the deformation of printed parts. In this report, we study methods for minimizing deformations during the 3D printing process when using HP MJF technology. Various factors contributing to deformation´s prediction were investigated and different techniques for reducing them were explored.
Injection Moulding into 3D-Printed Plastic Inserts Produced Using the Multi Jet Fusion Method
(MDPI, 2023) Habrman, Martin; Chval, Zdeněk; Ráž, Karel; Kučerová, Ludmila; Hůla, František
Většina vstřikovaných plastů je vstřikována do forem vyrobených z konvenčních materiálů, jako je ocel nebo hliník. Pro úsporu nákladů lze použít 3D tisk z plastu pro vstřikovací formy. Tento článek se zabývá vstřikováním do 3D tištěné plastové formy. Vstřikovací vložka byla vyrobena na 3D tiskárně HP Multi Jet Fusion 4200. Druhá část formy byla vyrobena z hliníku. Pro výzkum byla navržena zakázková vstřikovací forma. V článku je řešeno porovnání vstřikování do plastových a hliníkových vložek. Rozdíl při vstřikování do plastové vložky je vysvětlen pomocí rozdílných technologických podmínek.
Improved extrapolation method for the fatigue damage of bus structural steel under service loading
(Korean Society of Mechanical Engineers, 2021) Dewa, Rando Tungga; Kepka, Miloslav
Various Approaches to Reduce Consequences of Pedestrian-Tram Front End Collision
(University of Zagreb, Faculty of Transport and Traffic Sciences, 2023) Ježdík, Roman; Kemka, Vladislav; Kovanda, Jan; Lopot, František; Purš, Hynek; Hájková, Barbora
Bezpečnost kolejových vozidel je důležitou součástí udržitelné veřejné dopravy. Důkazem této snahy jsou nová doporučení a předpisy odborné komise (WG2 Technické komise CEN / TC 256) týkající se tramvají a lehkých kolejových vozidel se zaměřením na zranitelné účastníky dopravy. Další požadavky na bezpečnost tramvají si může vyžádat provozovatel vozidla a/nebo město. Opatření pro bezpečnost chodců mohou být převzata z oblasti automobilů využitím principů z předpisů EU č. 78/2009, EHK/OSN a testů EuroNCAP. Cílem publikace je představit zjednodušenou zkušební metodiku pro čelo tramvaje s ohledem na bezpečnost chodců, kde byla přijata metoda testování pomocí impatorů. Oblasti nárazu byly definovány obvodovými vzdálenostmi na svislém řezu karosérie. Matematický model byl vytvořen pro porovnání výsledků testů s figurínou, standardními a zjednodušenými hliníkovými impaktory. Uvedená metodika umožňuje testovat přední část tramvaje alternativní metodikou založenou na jednoduchém impaktoru a poskytuje účinný nástroj, který může výrobce a provozovatele tramvají inspirovat ke zvýšení bezpečnosti zranitelných účastníků dopravy.
Effect of Forming and Heat Treatment Parameters on the Mechanical Properties of Medium Manganese Steel with 5% Mn
(MDPI, 2023) Leták, Radek; Jirková, Hana; Kučerová, Ludmila; Jeníček, Štěpán; Volák, Josef
Středně manganové oceli patří do kategorie moderních vysoko-pevných ocelí třetí generace. Díky svému legování využívají k dosažení svých mechanických vlastností řadu zpevňujících mechanismů. Tyto mechanismy jsou efekty TRIP a TWIP. Díky vynikající kombinaci pevnosti a tažnosti jsou vhodné i pro bezpečnostní součásti karoserií automobilů, jako jsou boční výztuhy. Pro experimentální program byla použita střední manganová ocel s 0,2 % C, 5 % Mn a 3 % Al. Plechy o tloušťce 1,8 mm bez povrchové úpravy byly tvarovány v lisovacím kalicím nástroji. Boční výztuhy vyžadují v různých částech různé mechanické vlastnosti. Na vyrobených profilech byla testována změna mechanických vlastností. Změny ve zkoušených oblastech byly vyvolány lokálním ohřevem do mezikritické oblasti. Tyto výsledky byly porovnány s klasicky žíhanými vzorky v peci. V případě nástrojového kalení byly mezní hodnoty pevnosti vyšší než 1450 MPa s tažností přibližně 15 %.
Effect of Temperature and Deformation on the Stability of Retained Austenite in Closed-die Forgings from High-strength Martensitic Manganese-silicon Steels
(Jan-Evangelista-Purkyne-University, 2023) Bublíková, Dagmar; Jirková, Hana; Stehlík, Adam; Jeníček, Štěpán
Zbytkový austenit je u moderních vysokopevných ocelí důležitou fází ve výsledné mikrostruktuře, která způsobuje kombinaci dobré pevnosti a tažnosti. Jedním z moderních postupů, kterým lze této kombinace dosáhnout, je Q-P proces (Quenching and Partitioning). Tímto postupem je možné dosáhnout pevnosti kolem 2000 MPa a tažnosti 10-15 %. Stabilitu zbytkového austenitu v martenzitické matrici ovlivňuje zejména chemické složení oceli, jeho morfologie, velikost a rozložení ve struktuře. Zápustkový výkovek byl vykován z experimetnální oceli s 0,42 % C, 2,45 % Mn, 2,09 % Si, 1,34 % Cr, 0,56 % Ni, který byl poté zpracován Q-P procesem. Na základě předchozích dat získaných z reálného procesu, byly na termomechanickém simulá-toru odzkoušeny dva modely tepelného zpracování, které se lišily rychlostí ochlazování. Po tepelném zpra-cování byla získána martenzitická struktura s obsahem zbytkového austenitu 13-17 %. Mez pevnosti se pohybovala v rozmezí 2100-2200 MPa s tažnostmi A5mm 8-15 %. Stabilita získaného austenitu byla testována při různých teplotních expozicích (200, 300, 400, -18, -196 °C) a po tváření za studena s různou rychlostí deformace (10-3, 10-1, 10 s-1). Podíl uhlíku v austenitu byl vypočítán na základě mřížkových parametrů zjištěných pomocí RTG difrakce.
General Reference and Design S-N Curves Obtained for 1.2709 Tool Steel
(MDPI, 2023) Böhm, Michal; Niesłony, Adam; Derda, Szymon; Owsiński, Robert; Kepka, Miloslav; Zetková, Ivana; Zetek, Miroslav; Houdková, Šárka; Prażmowski, Mariusz

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