Pusiau standžių mazgų iš medienos ir metalo elgsenos tyrimas ir modeliavimas

Disertaciniame darbe analizuojamas inovatyvios konstrukcijos pusiau standus mazgas, pagamintas iš klijuotosios medienos ir metalo, skirtas sijinių elementų tarpusavio jungčiai. Pagrindinis darbo tikslas – tai komponentų metodo pritaikymas analizuojamo pusiau standaus mazgo lenkiamosios galios ir sukamojo standžio skaičiavimuose. Pristatomas komponentų metodas yra išvestas remiantis plieninių konstrukcijų jungtims pateikiama metodika. Atskirų mazgo komponentų stiprio ir standžio išraiškos gaunamos modeliuojant jungtį tūriniais baigtiniais elementais bei atliekant konstrukcinių matmenų jungties eksperimentinius tyrimus. Disertaciją sudaro įvadas, keturi skyriai, bendrosios išvados, literatūros sąrašas, autoriaus publikacijų sąrašas disertacijos tema ir santrauka anglų kalba. Įvade aptariama tiriamoji problema, darbo aktualumas, tyrimo objektas. Suformuojami darbo tikslai bei uždaviniai, pateikiama tyrimų metodika, aptariamas darbo mokslinis naujumas ir pasiektų rezultatų praktinė reikšmė, pristatomi ginamieji teiginiai. Įvado pabaigoje pristatomos autoriaus paskelbtos mokslinės publikacijos, pranešimai konferencijose ir pateikiama disertacijos struktūra. Pirmame skyriuje pateikiama kitų autorių mokslinės literatūros analizė tiriamu klausimu bei pristatomas tiriamas pusiau standus mazgas, pagamintas iš klijuotosios sluoksninės medienos ir metalo. Antrame skyriuje pristatomi atlikti konstrukcinių matmenų analizuojamos jungties eksperimentiniai tyrimai. Aptariami galimi eksperimentiniai irties pobūdžiai, pateikiamos eksperimentinės lenkiamosios galios bei sukamieji standžiai. Trečiame skyriuje pateikiama mazgo skaitinė analizė naudojant baigtinių elementų metodą. Pateikiamas detalus jungties skaitinio modelio aprašymas ir atliekama parametrinė mazgo analizė, nustatanti atskirų parametrų poveikį bendrai mazgo lenkiamajai galiai ir sukamajam standžiui. Ketvirtame skyriuje pateikiamas komponentų metodo pritaikymas pusiau standaus mazgo, pagaminto iš medienos ir metalo, lenkiamosios galios ir sukamojo standžio skaičiavimuose. Pateikiamos kai kurių naujai siūlomų komponentų laikomosios galios ir standžio koeficientų išraiškos. Pristatomi parametrinės analizės rezultatai, gauti keičiant analizuojamo mazgo matmenis. Disertacijos tema paskelbti 8 moksliniai straipsniai, iš kurių du ISI Web of Science leidiniuose, turinčiuose citavimo indeksą; vienas ISI proceedings tarptautinės konferencijos medžiagoje; vienas recenzuojamoje užsienio tarptautinės konferencijos medžiagoje; trys straipsniai kitų tarptautinių duomenų bazių leidiniuose bei vienas straipsnis recenzuojamoje Lietuvos jaunųjų mokslininkų konferencijos medžiagoje

Rotational stiffness determination of the semi-rigid timber-steel connection

In this research, the component method implementation for determination of the rotational stiffness of timber-steel connection is shown. Component method is one of the most commonly used methods for determination of the bending moment-rotation relation which later may be used in the practical analysis of the connection. The component method is not widely used for the analysis of the semi-rigid timber connections. There are only several investigations previously done on the component method implementation for the timber connections and most of them are based on only one basic component, i.e. timber compression or glued-in steel rod in tension. This article presents a new investigation of rotational stiffness determination algorithm of the semi-rigid timber-steel connection, which is based on the component method. The component method’s mechanical model of the connection combines all components which have influence on the rotational stiffness of the connection. The analysed timber-steel connection is subjected to pure bending. Stiffness coefficients of the steel part components are determined according to the Eurocode 3: design of steel structures Part 1-8: Design of joints. The timber part components are derived from the full-scale laboratory experiments and finite element modelling results, presented in the previous publications of the authors. The presented rotational stiffness determination results are well in line with the experimental and finite element modelling results, published in the previous publications

In situ formation and photo patterning of emissive quantum dots in small organic molecules

Nanostructured composites of inorganic and organic materials are attracting extensive interest for electronic and optoelectronic device applications. Here we report a novel method for the fabrication and patterning of metal selenide nanoparticles in organic semiconductor films that is compatible with solution processable large area device manufacturing. Our approach is based upon the controlled in situ decomposition of a cadmium selenide precursor complex in a film of the electron transporting material 1,3,5-tris(N-phenyl-benzimidazol-2-yl)-benzene (TPBI) by thermal and optical methods. In particular, we show that the photoluminescence quantum yield (PLQY) of the thermally converted CdSe quantum dots (QDs) in the TPBI film is up to 15%. We also show that laser illumination can form the QDs from the precursor. This is an important result as it enables direct laser patterning (DLP) of the QDs. DLP was performed on these nanocomposites using a picosecond laser. Confocal microscopy shows the formation of emissive QDs after laser irradiation. The optical and structural properties of the QDs were also analysed by means of UV-Vis, PL spectroscopy and transmission electron microscopy (TEM). The results show that the QDs are well distributed across the film and their emission can be tuned over a wide range by varying the temperature or irradiated laser power on the blend films. Our findings provide a route to the low cost patterning of hybrid electroluminescent devices

Behaviour of vertical cylindrical tank with local wall imperfections

Design of modern thin-walled metal structures is widely used around the world. In recent decades, more comprehensive research is carried out to investigate the behaviour of various thin-walled structures. Generally, the structure with regular geometry is investigated. In various countries such as USA, Russia, and the European Union issued the standards on regulation of the construction, design and maintenance of thin-walled structures. The actually used period of tanks usually is longer than recommendatory period. Recommendatory maintenance period of metal tanks is 15–20 years. Therefore, for such structures one of the most considerable questions is the residual load bearing capacity beyond the end of the maintenance period. This phase of using of structures is associated with complex investigation and numerical analysis of thin-walled structures. In this paper the load bearing capacity of the steel wall of the existing over-ground vertical cylindrical tank in volume of 5,000 m3 with a single defect and with a few contiguous local defects of the shape is analyzed. Calculations carried out are taking into account all the imperfections of the wall geometry. A major goal of the research – developing a realistic numerical model of the object analyzed, taking into account all the imperfections, determining the wall stress and strain state, exploring the places of extreme points, calculating the residual load bearing capacity of the tank and scrutinizing possible strengthening schemes for defective areas

Laser-induced spatially-selective tailoring of high-index dielectric metasurfaces

Optically resonant high-index dielectric metasurfaces featuring Mie-type electric and magnetic resonances are usually fabricated by means of planar technologies, which limit the degrees of freedom in tunability and scalability of the fabricated systems. Therefore, we propose a complimentary post-processing technique based on ultrashort (= 10 ps) laser pulses. The process involves thermal effects: crystallization and reshaping, while the heat is localized by a high-precision positioning of the focused laser beam. Moreover, for the first time, the resonant behavior of dielectric metasurface elements is exploited to engineer a specific absorption profile, which leads to a spatially-selective heating and a customized modification. Such technique has the potential to reduce the complexity in the fabrication of non-uniform metasurface-based optical elements. Two distinct cases, a spatial pixelation of a large-scale metasurface and a height modification of metasurface elements, are explicitly demonstrated. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

CIGS thin-film solar module processing: case of high-speed laser scribing

In this paper, we investigate the laser processing of the CIGS thin-film solar cells in the case of the high-speed regime. The modern ultra-short pulsed laser was used exhibiting the pulse repetition rate of 1 MHz. Two main P3 scribing approaches were investigated – ablation of the full layer stack to expose the molybdenum back-contact, and removal of the front-contact only. The scribe quality was evaluated by SEM together with EDS spectrometer followed by electrical measurements. We also modelled the electrical behavior of a device at the mini-module scale taking into account the laser-induced damage. We demonstrated, that high-speed process at high laser pulse repetition rate induced thermal damage to the cell. However, the top-contact layer lift-off processing enabled us to reach 1.7 m/s scribing speed with a minimal device degradation. Also, we demonstrated the P3 processing in the ultra-high speed regime, where the scribing speed of 50 m/s was obtained. Finally, selected laser processes were tested in the case of mini-module scribing. Overall, we conclude, that the top-contact layer lift-off processing is the only reliable solution for high-speed P3 laser scribing, which can be implemented in the future terawatt-scale photovoltaic production facilities