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- ItemEffect of different strain rates on mechanical behavior and structure of Inconel 718 produced by powder bed fusion(Springer Nature, 2024-07-27) Kolomý, Štěpán; Benč, Marek; Harant, Martin; Sedlák, Josef; Jopek, MiroslavThe paper aims to examine the effect of different strain rates on a mechanical behavior and structure of additively manufactured Inconel 718. The material was prepared by the powder bed fusion method, which is commonly employed for high-performance components subjected to both high static and dynamic loading. To analyze the material's behavior at various strain rates, a conventional hydraulic testing machine and a split hopkinson pressure bar apparatus were utilized. Additionally, the effect of these conditions on mechanical properties and microstructure was investigated. Results of compressive tests revealed a positive strain rate sensitivity of the material. Furthermore, the microhardness exhibited an increase by 33.9% in the horizontal direction after deformation caused by 210-2 strain rate and 35.8% in the vertical direction, respectively. Additionally, the average grain size decreased by 43.3%, and the high-angle grain boundaries decreased by 5.4% in the horizontal direction after the excessive plastic deformation at the strain rate of 1.8103 s-1. Scanning electron microscopy images showed that the as-built structure predominantly consisted of Laves phases in a long strip shape, while the structure after dynamic testing featured a granular shape. Transmission electron microscopy analysis of a sample tested at strain rate of 0.002 s-1 revealed finely developed grains within the structure, many of which contained a dislocation substructure. This study's novelty and robustness lie in its significant contribution to practical industrial energy applications, in which parts are exposed to dynamic load such as gas turbines.
- ItemResidual Stress Distribution in Dievar Tool Steel Bars Produced by Conventional Additive Manufacturing and Rotary Swaging Processes(MDPI, 2024-11-22) Izák, Josef; Strunz, Pavel; Levytska, Olena; Németh, Gergely; Šaroun, Jan; Kocich, Radim; Pagáč, Marek; Tuharin, KostyantynThe impact of manufacturing strategies on the development of residual stresses in Dievar steel is presented. Two fabrication methods were investigated: conventional ingot casting and selective laser melting as an additive manufacturing process. Subsequently, plastic deformation in the form of hot rotary swaging at 900 degrees C was applied. Residual stresses were measured using neutron diffraction. Microstructural and phase analysis, precipitate characterization, and hardness measurement-carried out to complement the investigation-showed the microstructure improvement by rotary swaging. The study reveals that the manufacturing method has a significant effect on the distribution of residual stresses in the bars. The results showed that conventional ingot casting resulted in low levels of residual stresses (up to +/- 200 MPa), with an increase in hardness after rotary swaging from 172 HV1 to 613 HV1. SLM-manufactured bars developed tensile hoop and axial residual stresses in the vicinity of the surface and large compressive axial stresses (-600 MPa) in the core due to rapid cooling. The subsequent thermomechanical treatment via rotary swaging effectively reduced both the surface tensile (to approximately +200 MPa) and the core compressive residual stresses (to -300 MPa). Moreover, it resulted in a predominantly hydrostatic stress character and a reduction in von Mises stresses, offering relatively favorable residual stress characteristics and, therefore, a reduction in the risk of material failure. In addition to the significantly improved stress profile, rotary swaging contributed to a fine grain (3-5 mu m instead of 10-15 mu m for the conventional sample) and increased the hardness of the SLM samples from 560 HV1 to 606 HV1. These insights confirm the utility of rotary swaging as a post-processing technique that not only reduces residual stresses but also improves the microstructural and mechanical properties of additively manufactured components.
- ItemDevelopment of a test specimen carrier for the Taylor anvil test using 3D additive printing technology(Elsevier, 2024-10-01) Jopek, Miroslav; Müller, Samuel; Řiháček, JanDynamic material testing is increasingly crucial for establishing a comprehensive description of material models. One of the primary testing methods is the Taylor Anvil Test (TAT). In this test, strain rates of up to 10 5 s -1 can be achieved at impact speeds of 250 m/s. Proper evaluation of a specific material specimen in this test relies on delivering the test specimen to the impact point both centrally and perpendicularly, as well as at the moment of reaching the maximum impact speed. This Article addresses the development of a new carrier for round test specimens manufactured using additive 3D printing technology from a polyactide polymer adapted for the TAT device with a calibre of 17 mm. The Article closely examines the influence of geometric parameters of the carrier itself, optimized using the Ansys Fluid Flow software, with a focus on internal ballistics, particularly to achieve perpendicular impact and maximum impact speed without causing the destruction of the carrier. A new type of test carrier was designed and subsequently tested for round test specimens made of the aluminium alloy Al 2024T3, evaluating both the impact speeds of the carrier under identical initiation pressure parameters in the filling chamber and the impact speed parameters of the specimen, respectively, the strain rate of the test specimen.
- ItemCharacterization of randomly oriented strand boards manufactured from juvenile wood of underutilized wood species(Springer, 2024-04-27) Pipíška, Tomáš; Nociar, Marek; Král, Pavel; Ráheľ, Jozef; Bekhta, Pavlo; Réh, Roman; Krišťák, Ľuboš; Jopek, Miroslav; Pijáková, Barbora; Wimmer, Rupert; Šernek, MilanThe wood-based panel industry in Europe, which is dominated by the use of Norway spruce, will face new challenges due to environmental changes and the bark-beetle calamity, which started a new era of forestry. To explore the possibility of replacing spruce with other wood species, juvenile wood of nine underutilized wood species (Scots pine, European larch, poplar, willow, alder, birch, European beech, English oak and hornbeam) were used to make randomly oriented strand boards (OSBs). Single-layer OSBs were produced with 3% pMDI resin and 0.5% wax. Standard physical and mechanical properties were measured. The bending strength (MOR) values showed that there was no statistically significant difference between the values for, on the one hand, spruce (34.6 MPa) and, on the other, larch (25.9 MPa), poplar (25.2 MPa), willow (27.8 MPa), alder (34.3 MPa) or birch (27.1 MPa). A similar trend was found for the boards modulus of elasticity (MOE). The highest MOE values of 5,185 MPa and 4,472 MPa were found for spruce and alder, respectively. There was no significant difference between spruce and other wood species in internal bond strength. Boards made from high-density wood species showed better physical performance, whereas those made from low-density wood species (except pine) gave better mechanical properties. Strand-generalized characteristics, such as the slenderness ratio and specific surface, were analyzed for all investigated physical and mechanical properties. European larch, poplar, willow, and alder are potential wood species for manufacturing OSBs in future without mixing species, as they can replace spruce in the wood-based panel industry.
- ItemThe Effect of Additive Manufacturing on the Utility Properties of the Reducing Valve Rezistor(Jan Evangelista Purkyne University in Usti nad Labem, 2024-07-01) Řiháček, Jan; Císařová, Michaela; Peterková, EvaThe article is focused on the analysis of the additive technology (3D printing) applicability by using DMLS in the production of the reducing valve part, i.e. atmospheric resistor. Currently, the men-tioned part is produced by EDM in combination with soldering from the Inconel 718 steel. The use of additive technologies brings the assumption of greater flexibility and economy of production, which is verified by a set of analyzes focused on the accuracy of production and the utility properties of the mentioned part. In addition to technological aspects, such as individual production processes, economic aspects are also compared. Individual comparisons are the basis for assessing whether replacing the conventional production approach with 3D printing is advantageous in this case. The results of this assessment can subsequently be used for future applications of the considered additive manufacturing approaches in the case of similar components.