Scopus Publications
- Process robustness in reduced-time vacuum carburizing of automotive gear steels
Martin Klimeš, Jindřich Viliš, David Dobrocký, Jiří Procházka
International Journal of Advanced Manufacturing Technology, 2026
This study evaluated the influence of vacuum carburizing parameters on the microstructure, microhardness profile, and case hardening depth (CHD550) of TL 4227 and TL 4521 steels used in highly loaded gear components. Experiments were performed on industrial gear components using an ALD ModulTherm system at 960, 980, and 1,000 °C, followed by gas quenching and tempering. The work focused on industrial validation of VW TL gear steels and shortened carburizing cycles based on previous temperature-focused results. Metallographic examination and microhardness profiling were performed to establish correlations between process parameters and case properties. CHD550 increased from approximately 0.65 mm to 0.9 mm with increasing carburizing temperature, while surface hardness remained around 740 HV1. A reduction of the total carburizing cycle time by approximately 15–20% resulted in a limited decrease in CHD550 (9–12%), while surface hardness, martensitic microstructural homogeneity, and surface integrity were preserved. The carburizing regime at 980 °C provided the most balanced combination of case depth, hardness, and structural homogeneity. Moderate adjustment of carburizing temperature and cycle duration shortened the process while maintaining compliance with VW 50019:2011-05 under the studied industrial conditions and component geometries. - Comprehensive Evaluation of Layered Composite Protection Performance for Light Armored Vehicles
Jindřich Viliš, Krzysztof Kosiuczenko, Marek Nowakowski, Mirosław Tupaj, Andrzej Trytek, et al.
Journal of Materials Engineering and Performance, 2025
This study addresses the critical need for lightweight and effective ballistic protection in military applications, focusing on layered composite systems designed to meet NATO STANAG 4569 Level I standard. The layered ballistic protection combines Hardox 450 wear-resistant steel with Twaron CT 747 para-aramid fabric and Endumax Shield XF33 Ultra-High-Molecular-Weight polyethylene (UHMWPE). Three configurations of ballistic protection were evaluated, each differing in steel thickness and areal weight. Configurations 1 and 2, with 6-mm and 4-mm Hardox 450 steel, and areal weights of 84.3 kg/m2 and 68.6 kg/m2, respectively, successfully resisted 7.62-mm NATO FMJ M80 projectile impacts while maintaining structural integrity. Configuration 3, comprising 2-mm Hardox 450 steel (52.9 kg/m2), was not penetrated by the projectile but detached from the frame due to localized impact near the edge. Microscopic analysis identified delamination and cracking of the reinforcing fibers and matrix as dominant failure mechanisms. Combining experimental testing with numerical simulations confirms that these layered protection systems offer high ballistic resistance while maintaining low weight, offering significant advancements in the design of military vehicle protection systems. - Effects of Printing Angle, Infill Density and Cryogenic Pre-Treatment on the Tensile and Flexural Properties of FFF-Printed PLA
Jozef Jaroslav Fekiač, Lucia Kakošová, Michal Krbata, Marcel Kohutiar, Zbynek Studeny, et al.
Journal of Manufacturing and Materials Processing, 2025
Additive manufacturing of polymer materials, also known as 3D printing, is becoming a key technology for the production of functional parts with the ability to customize the structure and properties according to the application requirements. Polylactide (PLA) is one of the most commonly used materials in this field due to its biodegradability, ease of processing, and adequate strength for lightweight functional components. An important factor that affects the resulting properties of parts is not only the filler structure and density but also the angle at which the material is deposited during the printing process. This article focuses on investigating the influence of the printing angle (0°, 30°, 60° and 90°) and the bulk density of the filler (20%, 40%, 60% and 80%) on the mechanical properties of PLA samples. Two series of samples were prepared—the first was subjected to direct mechanical tests, and the second series was first exposed to freezing conditions and then tested to evaluate the effect of freezing on the material behavior. The samples were tested for tensile strength according to ASTM D638 and for bending strength according to ASTM D790. The results showed that the highest values were achieved in tensile strength in the 60°/80% configuration with a strength of 39.27 MPa, which represents more than a twofold improvement over the weakest configuration (0°/20%–19.58 MPa). In the bending test, the best results were achieved by the 90°/80% sample with a strength of 58.89 MPa, approximately 18% higher than 0°/20%. Cryogenic treatment caused a deterioration of all monitored parameters, especially at low infill densities and at an angle of 0°, where the decrease in strength reached up to 10–13%. These results confirm that the combination of a higher printing angle and a higher infill density is key to optimizing the mechanical properties of PLA parts, while cryogenic treatment has a negative impact on their behavior. - An Analytical Model for Ballistic Performance of Fiber-Reinforced Plastic Laminates
Bui Thanh Phan, Roman Vítek, Jindřich Viliš, Vladimír Horák
Applied Composite Materials, 2025
An analytical model is developed to predict the ballistic performance of fiber-reinforced plastic (FRP) laminates under normal impact of rigid penetrators with various nose shapes. The model formulation is based on the localized interaction model incorporated with the spherical cavity-expansion model. Experimental validation of the analytical model is performed on experimental data obtained by own ballistic tests on Twaron/epoxy laminates and previous studies on ballistic performance of other FRP laminates. The model predictions for the ballistic limits and residual velocities are in good agreement with the experimental data, with discrepancies remaining within 10%, demonstrating the robustness and reliability of the present model. - DEGRADATION EFFECTS OF SOLAR RADIATION ON THE MECHANICAL PROPERTIES OF COMPOSITE MATERIALS: AN EXPERIMENTAL INVESTIGATION
JINDRICH VILIS, PAVEL SAFL, BUI THANH PHAN, JAN ZOUHAR, ZDENEK POKORNY, et al.
Mm Science Journal, 2025
This study investigates the degradation of the mechanical properties of composite materials based on para-aramid fiber Twaron CT 747 due to prolonged exposure to sunlight. Composite samples were fabricated using three manufacturing technologies: vacuum-assisted resin transfer molding (VARTM), autoclave curing, and hot-pressing. The mechanical properties were characterized through uniaxial tensile testing and flexural tests. The testing included reference samples (unexposed) and samples exposed to sunlight for 31 days and 122 days. The reference samples exhibited tensile strengths of 586.4 MPa (VARTM), 492.8 MPa (autoclave), and 399.6 MPa (hot pressing). After 122 days of sunlight exposure, tensile strength decreased by 29.6% (VARTM), 35.2% (autoclave), and 45.7% (hot-pressing), with the most significant decline in tensile modulus observed in the hot-pressed samples. Sunlight exposure also led to a reduction in flexural characteristics. Fractography analysis via scanning electron microscopy revealed layer delamination and the formation of microcracks, confirming the adverse effects of sunlight on material integrity. The findings of this study highlight the significant impact of prolonged solar exposure on the mechanical integrity of composite materials intended for outdoor applications. - The effect of changing the temperature of the vacuum carburizing process on the layer properties of steels used in the automotive industry
Jindřich Viliš, David Dobrocký, Zdeněk Joska, Jiří Procházka, Martin Klimeš
International Journal of Advanced Manufacturing Technology, 2025
This study examines the effects of vacuum carburizing temperatures ranging from 960 to 1000 °C on the properties of 16MnCr5 and 20NiMoCr6-5 steels, which are frequently employed in automotive manufacturing. Utilizing ALD ModulTherm equipment, controlled chemical heat treatment was conducted, achieving carbon saturation depths of 0.5 to 0.8 mm. The investigation focuses on critical parameters such as grain size, microstructure, and microhardness profiles to elucidate how these properties are influenced by temperature variations. The results demonstrate that carburizing temperature significantly alters the mechanical properties of the steels, particularly affecting microhardness and grain structure. Higher carburizing temperatures enhance microhardness but may also lead to undesirable coarsening effects in the austenitic grain structure. These findings highlight the importance of optimizing carburizing temperatures to improve the durability and overall functionality of automotive components. - UNMANNED VEHICLE MOBILITY IMPROVEMENT AGAINST BALLISTIC THREATS DURING SPECIAL MISSIONS: A SIMULATION STUDY
Marek Nowakowski, Krzysztof Kosiuczenko, Jindřich VILIŠ
Transport Problems, 2025
Implementing unmanned solutions in combat operations transforms battlefield dynamics by minimizing human risks. This study focuses on improving the ballistic protection of key elements in unmanned vehicles to enhance their mobility in hazardous areas. Advancements in unmanned ground vehicle technologies are described. The benefits of developing optionally unmanned vehicles for special purposes are indicated. The high-mobility manned-unmanned TAERO vehicle is introduced, and its structure and parameters are described. Operational limitations arising from potential threats during military missions are identified. Critical components requiring ballistic protection are selected, and the necessary protection levels are defined. Available materials for additional ballistic protection are described in relation to the NATO STANAG 4569 standard, which applies to logistic and light armored vehicles. Numerical analysis was conducted to evaluate the protection of key vehicle components using the lightest composite armors. This study is crucial for validating the effectiveness of the selected composite material and ensuring that its implementation meets the required standards for providing the desired level of ballistic protection for unmanned vehicles. The results confirm that the proposed solution improves the TAERO mobility in dangerous zones. - CHANGE IN MECHANICAL PROPERTIES OF BALLISTIC MATERIALS AFTER EXPOSURE TO EXTREME ENVIRONMENTS
Ondrej LINKA, Jindrich VILIS, Zbynek STUDENY
Metal International Conference on Metallurgy and Materials Conference Proceedings, 2025 - Manufacturing and Strength Evaluation of Composite Threads
Jan Zouhar, Radim Kupcak, Martin Vecerka, Jindřich Viliš
Solid State Phenomena, 2025
This study evaluates the direct machining of internal threads in glass fiber-reinforced (GFRP) and carbon fiber-reinforced (CFRP) composite materials, comparing the performance of cutting taps, conventional thread milling, and orbital thread milling. GFRP and CFRP samples were prepared and drilled under optimized conditions to minimize delamination, followed by thread production using the three different technologies. Visual and microscopic inspections revealed that orbital thread milling consistently produced the highest thread quality with minimal fiber damage, while cutting taps resulted in the most defects. Tensile testing showed that, in GFRP, orbital thread milling achieved the highest maximum load (18.05 kN), only slightly exceeding other methods. In CFRP, thread strength was similar across all technologies for 4 mm thick samples (around 4 kN), but increasing the thickness to 8 mm nearly doubled the strength, regardless of the threading method. The results demonstrate that orbital thread milling is optimal for thread quality, but in CFRP, material thickness is the dominant factor influencing joint strength. Direct threading in composites is feasible when appropriate machining parameters and technologies are applied. - Use of Integral Characteristics in the Evaluation of Surface Texture of Components after Plasma Nitriding
David Dobrocký, Zbynek Studeny, Jiří Procházka, Zdeněk Pokorný, Jindřich Viliš
Key Engineering Materials, 2025
The paper presents the use of integral methods of surface texture evaluation of structural steel samples used in armaments production for the analysis of the functional behaviour of gear surfaces. The aim of the paper is to evaluate the relationship between the quality of the ground surface and the surface after the plasma nitriding process and the functional properties of the surface using unconventional characteristics. These characteristics include Amplitude Distribution and Material Ratio, Autocorrelation Function (ACF), Frequency Spectrum (FS) and Power Spectral Density (PSD). These characteristics can, for example, reveal small changes in surface texture caused by both the cutting tool and surface treatments, such as diffusion nitriding technology, which show only slight changes in standard parameters. Thus, these characteristics can be used as a suitable diagnostic tool for evaluating changes in the functional properties of surfaces. These changes can usually be characterized by wavelength profile inequalities and statistical and spectral properties. In this paper, the surfaces of C45, 15NiCr13, 18CrNiMo7-6 and 16MnCr5 steels after the finishing operation of grinding and further after plasma nitriding are evaluated. Measurement of the standard parameter, i.e. the arithmetic mean height Ra, of ground and nitrided surfaces resulted in the same or slightly higher values after diffusion technology. Using integral characteristics, changes in surface texture were found to be directly related to the functional behaviour of surfaces in interaction and can predict, for example, noise levels, wear and lubrication properties. - Comparative Analysis of Metal Components Manufactured by WAAM Technology for the Strike Face Layer of Ballistic Protection
Jindřich Viliš, Zdeněk Pokorný, Jan Zouhar, Roman Vítek, Tomáš Fornůsek
Materials Science Forum, 2025 - INFLUENCE OF WATER ABSORPTION ON TENSILE AND FLEXURAL PROPERTIES OF COMPOSITE SAMPLES
Jindřich VILIŠ, David KUSMIČ, Bui Thanh PHAN, Jan ZOUHAR, Zdeněk POKORNÝ, et al.
Metal International Conference on Metallurgy and Materials Conference Proceedings, 2024 - Precision and Dimensional Stability of Bonded Joints of Carbon-Fibre-Reinforced Polymers Parts
Radim Kupčák, Jan Zouhar, Jindřich Viliš, Lukáš Gregor, Denisa Hrušecká
Applied Sciences Switzerland, 2023 - Analysis of Ballistic Impact of 7.62 mm FMJ M80 Rifle Projectile into Twaron/UHMWPE Composite Armor
Jindřich Viliš, Vlastimil Neumann, Roman Vítek, Jan Zouhar, Zdeněk Pokorný, et al.
Journal of Composites Science, 2023 - Experimental Investigation of Armour (Armox-Aramid-UHMWPE)
Jindřich Viliš, Roman Vítek, Jan Zouhar, Michal Stejskal, Vlastimil Neumann
Manufacturing Technology, 2023 - Ballistic Resistance of Composite Materials Tested by Taylor Anvil Test
Jindřich Viliš, Zdeněk Pokorný, Jan Zouhar, Miroslav Jopek
Manufacturing Technology, 2022 - TESTING THE BALLISTIC RESISTANCE OF COMPOSITE MATERIALS
Jindřich VILIŠ, Zdeněk POKORNÝ, Jan ZOUHAR
31st International Conference on Metallurgy and Materials Metal 2022, 2022 - Modification of Diffusion Layers by Laser Shock Peening
Jiri Prochazka, Jindrich Vilis, David Dobrocky, Petr Sperka
Manufacturing Technology, 2022 - Overview of tribological properties of UHMW polyethylene under rotation
Z. Studeny, D. Dobrocky, J. Viliš, J. Adam
Journal of Physics Conference Series, 2022 - Evaluation of ballistic resistance of thermoplastic and thermoset composite panels
J Viliš, Z Pokorný, J Zouhar, R Vítek, J Procházka
Journal of Physics Conference Series, 2022 - The Corrosion Resistance of Hard Anodised en AW 7075 T6 Alloy
David Kusmič, Lenka Klakurková, Martin Julis, Pavel Gejdoš, Jindrich Vilis, et al.
Ecs Transactions, 2021
