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Povzetek: Experimental tests of Cross Laminated Timber (CLT) under in-plane beam loading conditions are presented. The influence of the element layup, the individual lamination width, and the beam overhang at the supports on the shear force capacity was investigated. All the CLT beams had the same gross cross section, and a 4-point-bending test setup was used. The experimentally determined load-bearing capacities are compared with the load-bearing capacities resulting from analytical methods proposed for structural design, focusing on shear failure in the crossing areas of flatwise bonded laminations (shear failure mode III). The test results indicate no or very small influence of the element layup and the lamination width on the shear force capacity. These results partly contradict the predictions of the proposed design methods. Of the three studied beam geometry parameters, the beam overhang at the support had the greatest influence on the load-bearing capacity.
Ključne besede: cross laminated timber, CLT, beam, shear testing, shear capacity, design methods
Objavljeno v DiRROS: 15.04.2024; Ogledov: 64; Prenosov: 30
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Povzetek: The study reports the successful deposition of 15–5 precipitation-hardened (PH) martensitic steel on SAF 2507 duplex stainless steel (and vice versa) to form functionally graded materials (FGMs) using powder-based, directed-energy-deposition (DED) technology. The evolution of the microstructure and the mechanical properties of the 15–5 PH/SAF 2507 functionally graded material in the as-built state were investigated systematically. The results proved that the microstructural transition zone (MTZ) is formed above the fusion line due to the dilution effect of both steels. The phase composition of the MTZ consists of ferrite and, in comparison to the base materials, an increased amount of austenite. The interface has the lowest hardness owing to the formation of a significant proportion of the austenitic phase. However, the tensile mechanical properties were not affected by the interface as failure occurred in both SAF 2507 and at the interface regions. The research presents a promising application of FGMs in a horizontal configuration to form a high - quality, metallurgical joint between heterogeneous materials. This study introduces a novel approach by additive manufacturing (AM) of heterogeneous multi-materials, merging the favorable properties of duplex SAF 2507 and martensitic 15-5 PH stainless steels through superior metallurgical bonding. The combination of SAF 2507 and 15-5 PH in a functionally graded material has not been previously explored, as the existing studies deal with the duplex stainless steels SAF 2507 and either martensitic stainless-steel 15-5 PH deposited separately by laser powder-bed-fusion (L-PBF) or DED methods. This research pioneers the investigation of these materials in tandem, paving the way for the development of novel FGMs with optimized properties for specific applications. The resulting FGM exhibits exceptional corrosion resistance and high strength, making it highly versatile for applications in diverse industries such as offshore oil and gas production, aerospace, aviation, and chemical processing equipment.
Ključne besede: directed energy deposition, functionally graded materials, miniaturized specimen testing methods, SAF 2507, 15-5 PH
Objavljeno v DiRROS: 04.04.2024; Ogledov: 54; Prenosov: 18
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Povzetek: In vitro testing is the first important step in the development of new biomaterials. The human fetal osteoblast cell line hFOB 1.19 is a very promising cell model; however, there are vast discrepancies in cultivation protocols, especially in the cultivation temperature and the presence of the selection reagent, geneticin (G418). We intended to use hFOB 1.19 for the testing of Zn-based degradable metallic materials. However, the sensitivity of hFOB 1.19 to zinc ions has not yet been studied. Therefore, we compared the toxicity of zinc towards hFOB 1.19 under different conditions and compared it with that of the L929 mouse fibroblast cell line. We also tested the cytotoxicity of three types of Zn-based biomaterials in two types of media. The presence of G418 used as a selection reagent decreased the sensitivity of hFOB 1.19 to Zn2+. hFOB 1.19 cell line was more sensitive to Zn2+ at elevated (restrictive) temperatures. hFOB 1.19 cell line was less sensitive to Zn2+ than L929 cell line (both as ZnCl2 and extracts of alloys). Therefore, the appropriate cultivation conditions of hFOB 1.19 during biomaterial testing should be chosen with caution.
Ključne besede: zinc degradable materials, in vitro cytotoxicity testing, hFOB 1.19 osteoblasts
Objavljeno v DiRROS: 28.02.2024; Ogledov: 116; Prenosov: 48
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Povzetek: Immersion tests with different stainless steels have been performed, while the pH was stepwise decreased and then increased again. During 8.5-day exposure, the depassivation and repassivation pH values as a function of pitting resistance equivalent number were determined. There is always a gap between both pH values (depassivation and repassivation), indicating that for every steel, there are conditions where an existing passive layer can be maintained but cannot be rebuilt after depassivation. In such environments, the passive layer is thicker, consisting mainly of molybdenum and iron rich oxides, while chromium is dissolved. Usually, depending on conditions, the passive layer is more chromium-rich, especially the inner layer. This is relevant, for example, for acidizing jobs in oil and gas industry, proving that repassivation after acidizing will happen promptly, when the pH is increased again.
Ključne besede: stress corrosion cracking, surface finish impact, tapered tensile specimen, autoclave, accelerated testing, light water nuclear reactor, critical threshold stress
Objavljeno v DiRROS: 30.08.2023; Ogledov: 294; Prenosov: 149
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Povzetek: Non-native forest tree species have been introduced in Europe since the 16th century, but only in the second half of the 20th century the significance of the seed source origin for their economic use was recognized, resulting in the establishment of numerous provenance trials at a national, regional, European and International level, as those led by IUFRO. Breeding programs have also been launched in the continent for the most economically important species. Aim of this work is the formulation of provenance recommendations for planting of five non-native tree species in Europe (Douglas fir, grand fir, Sitka spruce, lodgepole pine and black locust), based on the information obtained from twenty countries, in the frame of the EU FP-1403 NNEXT Cost Action. The survey revealed that official and non-official national recommendations, based on provenance research results, have been elaborated and followed at a different level and extend for the above five species, but only for Douglas fir recommendations exist in almost all the participating to the survey countries. The compilation of provenance recommendations across Europe for each species is presented in the current work. Besides the recommended introduced seed sources, European seed sources are also preferred for planting, due to ease of access and high availability of forest reproductive material. European breeding programs yielding genetic material of high productivity and quality constitute currently the seed source of choice for several species and countries. Consolidation of trial data obtained across countries will allow the joint analysis that is urgently needed to draw solid conclusions, and will facilitate the development of ‘Universal-Response-Functions’ for the species of interest, rendering possible the identification of the genetic material suitable for global change. New provenance trial series that will test seed sources from the entire climatic range of the species, established in sites falling within and outside the environmental envelopes of their natural ranges, are urgently needed to pinpoint and understand the species-specific climate constraints, as well as to correlate functional traits to the seed origin and the environmental conditions of the test sites, so that the selection of suitable forest reproductive material of non-native tree species in the face of climate change can be feasible.
Ključne besede: provenance recommendations, provenance testing, breeding programs, adaptation, exotic tree species, Douglas fir, Sitka spruce, grand fir, lodgepole pine, black locust
Objavljeno v DiRROS: 09.02.2022; Ogledov: 811; Prenosov: 640
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