31. Parametarska studija kolničke konstrukcije ojačane geoćelijamaSamo Peter Medved, Bojan Žlender, Stanislav Lenart, 2018, original scientific article Abstract: U radu je prikazano parametarsko ispitivanje kolničke konstrukcije ojačane geoćelijama. Analiza temeljena na metodi konačnih elemenata uključuje model neojačane kolničke konstrukcije te model kolničke konstrukcije ojačane geoćelijama, pri čemu se analiziraju razni položaji, debljine i čvrstoća geoćelija. U okviru modela određen je i očekivani vijek trajanja kolničke konstrukcije. Rezultati parametarskog proučavanja u skladu su s rezultatima analitičkih rješenja, laboratorijskih i terenskih ispitivanja. Dobiveni rezultati upućuju na bitno poboljšanje nosivosti, smanjenje debljine asfaltnih slojeva i povećanje trajnosti kolničke konstrukcije kada je ona ojačana geoćelijama.
Published in DiRROS: 12.12.2023; Views: 177; Downloads: 120
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32. Klinične in histološke značilnosti ploščatoceličnega karcinoma kožePeter H. Soyer, Borut Žgavec, Bojan Popovič, 1999, review article Abstract: Ploščatocelični karcinom je druga najpogostejša maligna novotvorba kože. Najpomembnejši etiološki dejavnik je kronična izpostavljenost UV žarkom. Klinična slika je zelo raznovrstna, kar povzroča težave pri ločevanju teh tumorjev od drugih bolezni, predvsem pa bazalioma. Dokončno diagnozo postavimos histološko, v dvomljivih primerih pa uporabimo še imunohistokemičnopreiskavo.
Published in DiRROS: 28.11.2023; Views: 243; Downloads: 63
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34. Elucidating nucleation stages of transgranular stress corrosion cracking in austenitic stainless steel by in situ electrochemical and optical methodsSarmiento Klapper Helmuth, Bojan Zajec, Andreas Heyn, Andraž Legat, 2019, original scientific article Abstract: The pitting and environmentally assisted cracking resistance of austenitic stainless steels (SS) is challenged in several industrial applications particularly those involving hot chloride-concentrated streams. Directional drilling used in the oil and gas exploration is one of these applications. Indeed, high strength CrMn-SS commonly used in drilling technology have a high tendency to fail by stress corrosion cracking (SCC) preceded by localized corrosion once subjected to highly chloride-concentrated drilling fluids at elevated temperatures. A comprehensive understanding regarding the mechanisms governing the transition from pitting into SCCis not currently available, though. Therefore, mechanistic aspects such as the effect of loading conditions on pit nucleation and repassivation as well as the synergistic effect between pit stabilization and the nucleation of a stress corrosion crack are of great practical significance. To investigate this an electrochemical-, optical- and mechanical- monitored SCC test was conducted on a CrMn-SS in an alkaline brine at elevated temperature. The transition from metastable to stable pitting and subsequently to SCC in this system was documented in-situ for the first time. Results supported H.S. Isaacs postulates regarding the interpretation of electrochemical signals and demonstrated that loading conditions affect pit nucleation and repassivation leading to a higher susceptibility of the material to pitting, which preceded SCC.
Keywords: pitting corrosion, stress corrosion cracking, monitoring, elektrochemical noise, austenitic stainless steel
Published in DiRROS: 23.11.2023; Views: 221; Downloads: 178
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35. Activation and repassivation of stainless steels in artificial brines as a function of pHEmir Mujanović, Bojan Zajec, Tadeja Kosec, Andraž Legat, Stefan Hönig, Gerald Zehethofer, Gregor Mori, 2019, original scientific article Abstract: When planning oil wells with stainless steel components, two possible reasons for depassivation have to be considered-chemical depassivation caused by acidizing jobs and mechanical depassivation caused by various tools and hard particles. The study explores conditions causing chemical activation of investigated steels and circumstances under which repassivation occurs after activation. The main focus of the study is to determine, how quickly various steels can repassivate under different conditions and to find pH values where repassivation will occur after depassivation. The investigated steels were ferritic (martensitic or bainitic) in the cases of 13Cr, 13Cr6Ni2Mo, and 17Cr4Ni2Mo, austenitic in the case of 17Cr12Ni2Mo, and duplex (austenitic and ferritic) in the case of 22Cr5Ni3Mo. Potentiodynamic experiments were employed to obtain electrochemical properties of investigated steels, followed by immersion tests to find ultimate conditions, where the steels still retain their passivity. After obtaining this information, scratch tests were performed to study the repassivation kinetics. It was found that repassivation times are similar for nearly all investigated steels independent of their chemical composition and microstructure.
Keywords: stainless steels, activation, repassivation
Published in DiRROS: 21.11.2023; Views: 252; Downloads: 122
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36. Monitoring the galvanic corrosion of copper–steel coupling in bentonite slurry during the early oxic phase using coupled multielectrode arraysTadeja Kosec, Miha Hren, Klara Prijatelj, Bojan Zajec, Nina Gartner, Andraž Legat, 2023, original scientific article Abstract: In the case of a two-part container for spent nuclear fuel, consisting of an iron-based inner structure with a copper coating, the potential perforation of copper through minor damage may result in intensive galvanic corrosion between copper and steel. The present work focuses on the corrosion of steel galvanically coupled to copper and exposed to a slightly saline environment under oxic conditions. The electrochemical processes on individual electrodes were monitored by coupled multielectrode arrays (CMEAs). The CMEAs were either in contact with groundwater saturated with bentonite or immersed in groundwater only. Very high galvanic corrosion currents were detected between carbon steel and pure copper in the early oxic phase. Additionally, the use of CMEAs further made it possible to monitor the distribution of cathodic currents around the steel electrode, which behaved anodically. Various microscopy and spectroscopy techniques were applied to identify the modes of corrosion and the type of corrosion products present at the end of the period of exposure.
Keywords: copper, steel, bentonite, Aspö groundwater, coupled multi electrode array, electrochemical properties, Raman analysis, corrosion
Published in DiRROS: 16.11.2023; Views: 344; Downloads: 56
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37. Hierarchical learning of robotic contact policiesMihael Simonič, Aleš Ude, Bojan Nemec, 2023, original scientific article Abstract: The paper addresses the issue of learning tasks where a robot maintains permanent contact with the environment. We propose a new methodology based on a hierarchical learning scheme coupled with task representation through directed graphs. These graphs are constituted of nodes and branches that correspond to the states and robotic actions, respectively. The upper level of the hierarchy essentially operates as a decision-making algorithm. It leverages reinforcement learning (RL) techniques to facilitate optimal decision-making. The actions are generated by a constraint-space following (CSF) controller that autonomously identifies feasible directions for motion. The controller generates robot motion by adjusting its stiffness in the direction defined by the Frenet–Serret frame, which is aligned with the robot path. The proposed framework was experimentally verified through a series of challenging robotic tasks such as maze learning, door opening, learning to shift the manual car gear, and learning car license plate light assembly by disassembly.
Keywords: autonomous robot learning, learning, experience, compliance and impedance contro
Published in DiRROS: 21.09.2023; Views: 403; Downloads: 202
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39. Depassivation and repassivation of stainless steels by stepwise pH changeEmir Mujanović, Bojan Zajec, Andraž Legat, Tadeja Kosec, Janez Kovač, Gregor Mori, Stefan Hönig, Gerald Zehethofer, 2020, original scientific article Abstract: 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.
Keywords: stress corrosion cracking, surface finish impact, tapered tensile specimen, autoclave, accelerated testing, light water nuclear reactor, critical threshold stress
Published in DiRROS: 30.08.2023; Views: 300; Downloads: 155
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40. Stress corrosion crack initiation testing with tapered specimens in high-temperature water - results of a collaborative research projectRik-Wouter Bosch, Stefan Ritter, Matthias Herbst, Renate Kilian, Grace Burke, Jonathan Duff, Fabio Scenini, Yuchen Gu, Alice Dinu, Ulla Ehrnsten, Aki Toivonen, Radek Novotny, Oliver Martin, Francisco Javier Perosanz, Andraž Legat, Bojan Zajec, 2020, original scientific article Abstract: The applicability of an accelerated test technique using tapered tensile specimens for investigating the stress corrosion crack (SCC) initiation behaviour of structural materials in high-temperature water was assessed in the framework of a European collaborative research project (MICRIN – MItigation of CRack INitiation). The main advantage of using a tapered geometry is, that in a single test a stress gradient is obtained through the gauge length, and therefore a stress threshold for SCC initiation can be determined in a reasonable timeframe. This method was used to investigate two different materials that were known to be susceptible to SCC in light water reactor environment: a high-Si stainless steel and a Ni-base weld metal (Alloy 182). The results of the international test programme confirmed that the tapered specimen test methodology could be used to identify a SCC initiation stress threshold, albeit that significant scatter was present in the data.
Keywords: stress corrosion cracking, surface finish impact, tapered tensile specimen, autoclave, accelerated testing, light water nuclear reactor, critical threshold stress
Published in DiRROS: 28.08.2023; Views: 275; Downloads: 148
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