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Polymer-based composites find applications in several areas because of their exceptional properties. This article deals with Taguchi grey relational optimization method of abrasive parameters (load (L), grit size (G) and sliding distance (D)) and their influence on abrasive performance of reinforced polytetrafluoroethylene (PTFE) composites. A Taguchi L9 orthogonal array was designed, and nine experimental tests were conducted based on the Taguchi designed experiments. A pin-on-disc tribology machine was used for the experiments. The coefficient of friction (µ) and abrasive specific wear rate (Aw) were recorded for each experiment. An analysis of variance (ANOVA) was performed to establish the significance and percentage contribution of each parameter affecting the abrasive wear performance. Results from the Taguchi-grey-relational method showed that the optimal combination of parameters was achieved at load of 10 N, grit size of 1000 mesh, and sliding distance of 350 m (coded as L3G1D3). ANOVA findings revealed that a grit size with 67.69 % as the most influential on the abrasive performance of polymer-based composites. Validation tests performed using the optimal combination parameter showed an enhancement of 55.22 % in grey relational grade.

S povečevanjem uporabe polimernih kompozitov v letalski industriji se je povečalo tudi zanimanje za hibridne lepljene spoje, kjer se s pomočjo epoksidnih lepil spajajo kompoziti in aluminij. Spoji so lahko dodatno varovani, kar je bilo v tej raziskavi izvedeno z uporabo različnih kompozitnih sornikov. Prednost hibridnih spojev je predvsem v lahki in kompaktni konstrukciji, sloj lepila pa služi tudi kot izolator med različnima materialoma in preprečuje pojav galvanske korozije. V nalogi je bila ugotovljena višja trdnost adhezijskega spoja brez varovanja od spoja z varovanjem s sornikom, razlog za to je v zmanjšani površini lepljenja in nesočasnem prenosu sile adhezijskega in oblikovnega spoja. Višjo trdnost smo dosegali pri spojih varovanih s sornikom iz ogljikovih vlaken, saj ima manjši modul elastičnosti kot aramid, kjer je posledično prišlo do zamika prenosa sile. Laminati, izdelani z vakuumsko infuzijo, so po trdnosti primerljivi s spoji z industrijskim lepilom. Na prelomnih površinah je bila ugotovljena delaminacija plasti ogljikovih vlaken v epoksidni matrici in variiranje debeline sloja lepila, industrijsko lepilo je zdržalo vse predpisane obremenitve. With increased use of polymer composites in the aerospace industry, there has also been increased interest in development of hybrid adhesive joints, such as composites and aluminum, bonded with epoxy adhesives. Joints can be additionally protected against detachment, in this study we used different composite bolts. The main advantage of such joints is in lightweight construction, a layer of adhesive also serves as an insulation between different materials, which prevents galvanic corrosion. In this paper we prove better strength of adhesive joints without pin that secures joints from breaking, the main reason for that is in reduced gluing surface and uneven transmission of force. Higher value of strength was obtained from joints with carbon fiber pin, because of its lower elastic module, than the aramid fiber pin, where there was a delayed transmission of force. Laminates that were made with vacuum infusion, are from the mechanical point of view comparable with glued joints. On the breaking surfaces we noticed mostly delamination of carbon fibers and uneven thickness of glue, the industrial glue withstood all the specified loads.

Laminated composites have so far received little attention as a potential material for gear drive applications. In the presented study, the thermomechanical performance of a newly developed type of epoxy impregnated, autoclave-cured carbon fibre-reinforced polymer gear—running in pair with a steel pinion—was analysed, using a combination of experimental and numerical approaches. The employed methods enabled the identification of the composite’s mechanical, thermal, and tribological characteristics, as related to the studied gear pair application. A newly proposed, finite-element-analysis-based iterative procedure enabled an implicit evaluation of the analysed material pair’s coefficient of friction (COF), which is a key parameter in determining the gear pair’s thermomechanical characteristics. For the considered material pair, a value of 0.34 was identified for the coefficient in the quasi-steady region. As the coefficient is strongly correlated with frictional heat generation and significantly affects the surface shear stress, it can consequently have a meaningful influence on the composite’s wear rate. The developed COF identification procedure was validated using a reciprocating cylinder-on-flat tribological test method. The composite gear’s service life was additionally tested at various running loads, resulting in pitch contact pressures ranging between 400 and 540 MPa. Lifetime gear test results showed a markedly superior performance compared to the high-temperature thermoplastic polyether ether ketone, which is typically employed in the most demanding polymer gear applications. Several methods are additionally proposed that could further improve the developed composite gears’ performance.

V okviru zaključne naloge smo se seznanili s procesom vakuumske infuzije, ki ji sledi še obdelava v avtoklavu. Naš namen je bil določiti čim boljše izdelovalne parametre za doseganje dobrih mehanskih lastnosti kompozita. Glavni cilj naloge je bil določiti optimalno razmerje ogljikovih vlaken in epoksi smole ter opredeliti prispevek avtoklava na izboljšanje upogibne trdnosti tako izdelanega kompozitnega vzorca. Poleg tega smo z analizo mikroskopskih slik določili vpliv avtoklava na poroznost kompozita, tako na površini kot po preseku. Mehanske lastnosti smo preverjali s tritočkovnim upogibnim preizkusom. Z večanjem količine smole do določenega volumskega razmerja se po postopku vakuumske infuzije mehanske lastnosti kompozita izboljšujejo. Ob dodatni uporabi avtoklava pa je bila za doseg enakih mehanskih lastnosti kompozita potrebna manjša količina smole. Avtoklav je pozitivno vplival tudi na stopnjo poroznosti v kompozitu, saj jo je v primerjavi z vzorci, izdelanimi brez avtoklava, zmanjšal v vseh vzorcih. As part of the final task, we became acquainted with the process of vacuum infusion, followed by processing in autoclave. Our intention was to determine the best production parameters for the achievement of good mechanical properties of composite. The main objective of the task was to determine the optimal ratio of carbon fibre and epoxy resin and to define the contribution of the autoclave to improving the bending strength of the composite sample thus produced. In addition, microscopy was used to determine the impact of the autoclave on the porosity of composite, both on the surface and after the cross-section. Mechanical properties were checked by a three-point bending test. We found that by increasing the resin volume to a certain volume ratio after the vacuum infusion process, the mechanical properties of composite improved. However, when the autoclave was used, smaller amount of resin was required to achieve the same mechanical properties of the composite. Autoclave also had a positive effect on the porosity rate in the composite, as it decreased in all samples compared to samples manufactured without autoclave.

V zadnjem času kompozitni materiali dobivajo velik pomen, saj so postali nepogrešljivi v vesoljski, letalski in vojaški tehniki. Močno pa so se tudi že uveljavili v avtomobilski industriji ter pri izdelavi športnih rekvizitov. Zaradi vse večjega nadomeščanja klasičnih konstrukcijskih materialov s kompozitnimi ter nehomogenosti le teh se pojavljajo izzivi na področju določanja materialnih lastnosti. V zaključni nalogi je prikazan proces določanja efektivnega modula elastičnosti slojevite kompozitne sendvič strukture. V nalogi obravnavamo napetostno in deformacijsko stanje v prerezu kompozitnega nosilca. Izdelani so bili vzorci slojevite kompozitne sendvič strukture, na katerih smo izvedli 3-točkovni upogibni test. Opravljena je bila primerjalna analiza med rezultati analitičnega preračuna, ki smo ga naredili s pomočjo znanih mehanskih lastnosti posameznih komponent kompozita ter rezultati eksperimentalnega testa. Zaradi dobre primerljivosti rezultatov lahko trdimo, da je možno iz znanih mehanskih lastnosti komponent teoretično zelo dobro napovedati efektivni modul elastičnosti kompozitov. Composite materials are gaining more and more importance, as they have become indispensable in aerospace and military applications. But they have also become strongly established in the automotive industry and in the manufacture of sports equipment. Due to the increasing replacement of classical construction materials by composite materials and their inhomogeneity, challenges arise in the field of determining material properties. In this thesis the method for determining the effective modulus of elasticity of a layered composite sandwich structure is presented. The stress and strain state in the cross section of a composite beam is considered. Samples of a layered composite sandwich structure were fabricated and a 3-point bending test was performed on them. A comparative analysis was performed between the results of the analytical calculation, carried out with the known mechanical properties of each component of the composite, and the results of the experimental test. Due to the good comparability of the results, it can be argued that it is theoretically possible to predict the effective modulus of elasticity of composite materials very well from the known mechanical properties of the components.

Uvod: Ogljikova vlakna uporabljamo kot ojačitveni material v polimernih kompozitih. Pridobivamo jih na različne načine, zaradi svojih lastnosti pa so nepogrešljivi v letalski, ladijski, vesoljski, športni in strojni industriji, nenazadnje pa tudi v ortotiki in protetiki, predvsem z namenom zmanjševanja mase in večanja trdnosti ortotičnega oziroma protetičnega pripomočka. V primerjavi z ostalimi termoplastičnimi materiali so polimernimi kompoziti, ojačeni z ogljikovimi vlakni precej dražji. Namen: Namen diplomskega dela je pregled literature na področju polimernih kompozitov, ojačenih z ogljikovimi vlakni, ter določitev prednosti in slabosti le-teh v primerjavi s kompoziti, ojačenimi z drugimi vlakni pri uporabi v ortotiki in protetiki. Metode dela: Uporabljena je bila deskriptivna metoda dela s študijem domače in tuje literature. Uporabili smo različne podatkovne baze, kot so: Springer Link, Emerald Group Publishing Limited, Sage publication, Google Scholar in Cobiss. Rezultati: Za izbiro optimalnih materialov za ortoze in proteze upoštevamo njihove lastnosti, kot so gostota, trdnost, vzdržljivost, biokompatibilnost in druge. Razprava in zaključek: Z uporabo ogljikovih vlaken zagotovimo manjšo maso, manjšo debelino in večjo trdnost protetičnega ležišča v primerjavi z neojačenimi termoplastičnimi materiali. Pomembno je posvečanje pozornosti v raziskave na področju uporabe ogljikovih vlaken v ortotiki in protetiki, predvsem zaradi izboljšanja posameznega ortotičnega ali protetičnega pripomočka. Introduction: Carbon fibers are used as reinforcing material in polymer composites. They are obtained in various ways, and due to their properties they are indispensable in the aerospace, marine, space, sports, and engineering industries, as well as in orthotics and prosthetics, mainly with the aim of reducing the weight and increasing the rigidity of the orthotic or prosthetic device. Compared to other thermoplastic materials, carbon-reinforced polymer composites are much more expensive. Purpose: The purpose of this thesis is to review the literature in the field of polymer composites reinforced with carbon fibers, and to determine their advantages and disadvantages for use in orthotics and prosthetics compared to composites reinforced with other fibers. Methods: A descriptive methodology was used by studying national and international literature. Various databases were utilized such as: Springer Link, Emerald Group Publishing Limited, Sage publication, Google Scholar and Cobiss. Results: When selecting the optimal materials for orthoses and prostheses, their properties, such as density, strength, durability, biocompatibility and others must be taken into account. Discussion and conclusion: The use of carbon fibers in prosthetic sockets ensures lesser weight and thickness, and greater rigidity compared to non-reinforced thermoplastic materials. It is important to keep an eye on the research in the field of carbon fiber use in orthotics and prosthetics, with the aim of improving individual orthotic or prosthetic device.

V diplomskem delu smo naredili pregled literature o kompozitih, laminatih in lahkih sendvič panelih. Raziskali smo tri tehnološke postopke izdelave lahkih strukturnih sendvič plošč in njihov vpliv na kakovost izdelave. Ugotavljali smo vplive parametrov izdelave na upogibno trdnost in debelino sendvič kompozita. Testiranje je potekalo z dvema materialoma polnila, peno in satjem, obdana z enoslojno prepreg (pred-impregnirano) tkanino iz ogljikovih vlaken na vsaki strani. Iz posamezne serije plošč so bili izrezani standardni vzorci katere smo stehtali, premerili in stestirani s tri-točkovnim upogibnim preizkusom. Ugotovili smo, da se v območju med 0 in 5 barov delovnega tlaka v avtoklavu postopno zmanjšuje debelina sendvič plošče. Še posebej izrazito se je to pokazalo pri vzorcih iz pene, ki ima slabšo tlačno trdnost od satja. Po drugi strani pa smo ugotovili manjši padec debeline z naraščanjem tlaka pri vzorcih iz satja, v tem primeru je porušitev sledila šele pri najvišjih tlakih. Na upogibnem preizkusu se je najbolje obnesel vzorec iz satja pri tlaku 2 barov, najslabše pa sta se obnesla vzorca izdelana, sicer z zelo pogosto uporabljenim postopkom v industriji, naknadnim lepljenjem. Vzorci iz satja so dosegli tudi največje razmerje med maksimalno napetostjo in težo. Z mikroskopiranjem smo nato želeli rezultate dodatno ovrednotiti in ugotovili, da je je najbolj dominantna porušitev pri vzorcih, ki so lepljeni naknadno, delaminacija, pri ostalih pa kombinacija porušitve sredice in prekinitev vlaken pod točko obremenitve zaradi uklona na tlačni strani. In the thesis we have reviewed the literature on composites, laminates and light sandwich panels. We learned about three processes of making a very light structural sandwich panels, which we later used in the research with the desire to optimize the manufacturing process. With different parameters we wanted to observe the impact on bending strength and thickness. The testing was carried out with two core materials, foam and honeycomb, surrounded by a single-layer prepreg carbon fibre fabric on each side. Standard samples were cut out of each series of plates, which were weighed, measured and tested with a three-point bending test. We found that in the range of 0 to 5 bar working pressure in the autoclave gradually reduces the thickness of the sandwich plate. This was particularly pronounced in the samples of foam, which has a less compressive strength than a honeycomb. On the other hand, we found a slight decrease in thickness with an increase in pressure in honeycomb samples, in which case the failure was followed only at the highest pressures. The bending test results were the best of honeycomb at a pressure of 2 bar, and the worst was the panel produced, otherwise with a very commonly used industry process, subsequent gluing. Honeycomb samples also achieved the maximum ratio of bend strength compared to weight. With microscopy, we then wanted to further evaluate the results and found that the most dominant failure in samples glued afterwards is delamination, while in others the combination of core failure and the break of the fibres below the load point.

Ogljikova vlakna so snovi, zgrajena iz ogljikovih atomov in imajo izjemne lastnosti, predvsem, ko sestavljajo kompozit. Njihova izdelava je zahtevna, toda končni produkt je kakovosten in zaradi tega dosega tudi visoke cene na trgu. Ogljikova vlakna so kar petkrat močnejša od železa, imajo visoko trdnost in so korozijsko odporna. So odlično električno prevodna, imajo visoko natezno trdnost in nizek koeficient toplotnega raztezka. Niso škodljiva za človeka in kar je skoraj najboljša lastnost, so nevnetljiva. Čeprav so ogljikova vlakna nevnetljiva, je vnetljivost še vedno velik problem, ko ogljikova vlakna združujemo v polimerne kompozite. Poznamo tri najpogostejše polimerne osnove, ki se uporabljajo v kompozitih. To so epoksi, vinilester in poliesterska smola (poliesterska smola je le redko uporabljena z ogljikovimi vlakni). Vsak kompozit ima polimerno osnovo, ki je vnetljiva, zato se za visoko stopnjo nevnetljivosti, kompozitom dodajajo snovi, ki vnetljivost zavirajo. Pravimo jim zaviralci gorenja. Zaviralce gorenja lahko nanašamo v kompozit na različne načine. Lahko jih vmešamo v polimer med procesom izdelave, lahko jih kemijsko vgradimo v glavno polimerno verigo. Uporabimo lahko tudi zaviralce gorenja, ki se nanašajo kot zaščitna plast ali pa sami od sebe tvorijo zaščitno last, ko pridejo v stik z dovolj visokimi temperaturami. Zaviralce gorenja v splošnem delimo na fosforjeve, dušikove, halogenske, intumescenčne ter anorganske. Halogenski zaviralci gorenja temeljijo na dveh elementih, kloru in bromu, anorganski pa na aluminiju in magneziju. Anorganski zaviralci gorenja večinoma dodajamo le kot katalizatorje, da pospešijo delovanje drugih zaviralcev gorenja, ki so dodani kompozitu. Intumescenčni zaviralci gorenja ob povišanih temperaturah tvorijo zaščitno plast, ki varuje kompozit pred vžigom in razpadom. Za polimerne kompozite z ogljikovimi vlakni se večinoma uporabljajo halogenski in fosforjevi zaviralci gorenja. Prav fosforjevi zaviralci gorenja so začeli nadomeščati halogenske predvsem zato, ker so halogenski zaviralci gorenja škodljivi za človeka in okolje. Učinkovitost zaviralcev gorenja lahko določamo z različnimi tehnikami. Navadno merimo mejno vrednost kisika, to je koncentracija kisika, pri kateri snov še gori, lahko izvedemo skupino testov UL-94 ali pa s kalorimetrijo izmerimo sproščanje toplote in z rentgensko fotoelektronsko spektroskopijo spremljamo sestavo kompozita. Z dodajanjem zaviralcev gorenja kompozitnim materialom, se soočamo tudi z nevšečnostmi. Če pride do vžiga materiala in zaviralec ni učinkovit, lahko pride do učinka svečnega stenja, kjer gori polimer na ogljikovih vlaknih, vse dokler gorenje ni umetno prekinjeno oz. zmanjka goriva. Problem nastane tudi v polarnosti zaviralcev, kajti bolj polaren zaviralec gorenja kot polimerna osnova oslabi strukturo kompozita in privede do slabših mehanskih lastnosti. Danes se v kompozitih z ogljikovimi vlakni uporablja epoksi smola. Ker so materiali, zgrajeni iz epoksi smole lahki, lahko nadomestijo druge, prej težje materiale, kar je uporabno predvsem v letalski in avtomobilski industriji. Sprva so se takšnim kompozitom dodajali halogeni zaviralci gorenja, danes pa se zaradi nevarnosti vedno bolj uporabljajo fosforjevi. Potrebno je dobro poznati tako lastnosti zaviralcev gorenja kot tudi kompozita, da lahko dosežemo dobro odpornost proti vnetljivosti in tako še izboljšamo lastnosti polimernim kompozitom z ogljikovimi vlakni. Carbon fibres mainly consist of carbon atoms and they have some outstanding properties, especially when it is integrated in a composite. Although the production of carbon fibres is complex, the final product has great quality, which is why carbon fiber materials are expensive in the market. Carbon fibres are five times stronger than iron as well as rigid and corrosion resistant. Electric conductivity of carbon fibres and their tensile strength are high and thermal expansion coefficient is low. They are not poisonous for people in addition to not being flammable, which is one of their best features. Flammability, however is still a very big problem, when carbon fibres are put into polymer composites. There are three main polymer matrices, which can be used in polymer composites: epoxy resin, vinylester resin and polyester resin , which is rarely used with carbon fibres. Since almost every polymer has a polymer matrix which is flammable, special materials are added to the composites in order to make them non-flammable. They are called flame retardants and they can be integrated into composites in different ways. They can either be added to polymer matrix during the production process or they can be integrated in the main polymer chain. Flame retardants, which are added as protective coating or which form protective coatings during the exposure to high temperatures can also be used. In general, flame retardants can be divided to phosphorous, nitrogen, halogen, intumescent and inorganic flame retardants. Halogen flame retardants mainly contain one of two elements (chlorine or bromine) and inorganic flame retardants are generally made of aluminium or magnesium. Inorganic flame retardants are mostly used as catalysts, so they speed up the effect of other flame retardants added to the composite. Intumescent flame retardants create a protective layer at high temperatures, which protects composite from ignition and degradation. Mainly halogen and phosphorus flame retardants are used for polymer composites with carbon fibres. Since halogen retardants appear to be harmful to people and to the environment, phospohorous flame retardants started to be used as a substitute. Effectiveness of flame retardants can be determined by using various techniques. Most commonly the limiting oxygen index, and shows the percentage, where material still burns. In addition group of UL-94 tests can be performed or determine heat release with calorimetry or we can watch a chemical composition of product with x-ray photoelectron spectroscopy. Because of the addition of flame retardants to composite materials, several problems emerge. If the ignition of material happens and the flame retardants are not effective, a candlewick effect could happen. This means that the polymer is burning on carbon fibres until fire is turned down artificially or the fuel runs out. Another problem occurs in the polarity of flame retardants if flame retardant is more polar than polymer matrix, structure of composite becomes weak, which leads to bad mechanical properties. Nowadays, epoxy resin is mostly used in polymer composites with carbon fibres. Materials from such substances can replace other, heavier materials, which is very useful in aviation and automobile industry. Firstly, halogen flame retardants were added to such composites, and because halogen flame retardants are toxic, more and more phosphorus flame retardants are used. Properties of flame retardants and composites have to be well researched, so that good flame retardancy can be reached and that is how polymer composites with carbon fibres properties are even improved.

V okviru diplomskega dela smo zajeli vso literaturo na podlagi kompozitov njihovih lastnosti ter postopki izdelave, podrobneje smo se spoznali z dvema tehnološkima postopkoma izdelave kompozitnih materialov, s ciljem ugotavljanja vpliva tehnologije izdelave na strižno trdnost. Testiranje strižne trdnosti je potekalo na izrezanih vzorcih iz dveh plošč, izdelanih iz ogljikove tkanine ter epoksidne smole, z enakimi ploskovnimi dimenzijami, enako postavitvijo vlaken, enakimi materiali ter z dvema različnima postopkoma izdelave. Vzorce smo testirali na strižno trdnost s pomočjo tri-točkovnega strižnega preizkusa po standardu ASTM D 2344. Pri tem smo ugotovili, da so vzorci izdelani po vakuumski infuziji in dodatnim stiskanjem v autoclavu zdržali večjo strižno trdnost v primerjavi z mokro ročno laminacijo. Z mikroskopiranjem smo nato analizirali površinsko poroznost in mikrostrukturo vzorcev, kjer smo ugotovili, da kompozit, izdelan z vakuumsko infuzijo, zdrži večjo strižno trdnost predvsem zaradi manjše poroznosti in manj napak, katere vnesemo s postopkom mokre ročne laminacije. As part of the final work, we covered the literature based on composites their properties and manufacturing procedures, we got acquainted in detail with two technological procedures fort the production of composite materials with aim of determining the impact of manufacturing technology on shear strength. Shear strength testing was performed on cut-out samples from two plates, made of carbon fabric and epoxy resin, with the same surface dimensions, the same fiber placement, the same materials, and with two different manufacturing processes. The samples were tested for shear strength, using a tree-point shear test, according to standard ASTM D 2344. We found out that the samples, made with vacuum infusion with additional compression in an autoclave withstand higher shear strength, compared to wet/hand lay-up. The surface porosity and microstructure of the samples were then analysed with microscope, where it was found that the composite made by vacuum infusion withstands higher shear strength because of minor porosity and less flaws, which are entered by process of wet/hand lay-up lamination.

Grafen je enoslojna oblika grafita povezana z sp2 hibridiziranimi ogljikovimi atomi v heksagonalno kristalno strukturo. Grafenski nanotrakovi so trakovi grafena, ki imajo visoko razmerje med dolžino in širino in so sestavljeni iz ene ali več plasti grafena. Imajo kvazi 1D strukturo ter zanimive lastnosti – drugačne od grafena. Kljub debelini največ nekaj atomov, je eden izmed najtrših materialov, ki je hkrati odličen toplotni in električni prevodnik. Zaradi teh unikatnih lastnosti potekajo številne raziskave na področju izboljšanja mehanskih, toplotnih in električnih lastnosti materialov. Ena od možnih aplikacij grafenskih nanotrakov je izboljšanje mehanskih lastnosti kompozitnih materialov. Problem pri uporabi se pojavlja pri dispergiranju grafenskih nanotrakov v epoksi smolo, ki predstavlja ključen korak pri izdelavi kompozitnih materialov. S postopkom funkcionalizacije lahko modificiramo grafenske nanotrakove tako, da bo dispergiranje veliko učinkovitejše. S tem namenom sem v svojem magistrskem delu sintetiziral nefunkcionalizirane grafenske nanotrakove ter z epiklorohidrinom funkcionalizirane grafenske nanotrakove. Sledilo je dispergiranje pripravljenih nanotrakov v epoksi smolo ter izdelava kompozitnih materialov. S pomočjo karakterizacijskih metod sem ugotavljal uspešnost sinteze in funkcionalizacije, z mehanskimi meritvami pa ugotavljal, ali dodajanje grafenskih nanotrakov izboljša mehanske lastnosti kompozitnih materialov. Graphene in a single-layer form of graphite with sp2 hybridized carbon atoms bonded in hexagonal crystalline structure. Graphene nanoribbons are strips with high aspect ratio and may consist of one or more layers of graphene. They have a quasi 1D structure and possess additional interesting properties compared to graphene. Despite its thickness of just a few atoms, it is one of the most durable materials with excellent thermal and electrical properties. Because of these unique properties, many studies are underway to improve the mechanical, thermal and electrical properties of materials. One of the possible applications of graphene nanoribbons is the improvement the mechanical properties of composite materials. However, dispersibility of graphene nanoribbons into epoxy resin, which is a key step in the manufacture of composite materials, represents a barrier in application. Through the functionalization process graphene nanoribbons can be modified to enhance dispersibility. Herein, I synthesized non-functionalized graphene nanoribbons and graphene nanoribbons functionalized with epichlorohydrin. This was followed by the dispersion of the prepared nanoribbons into epoxy resin and the production of composite materials. The characterization methods were used to determine the yield of synthesis and degree of functionalization. Further, the mechanical measurements were done to determine mechanical properties of graphene based nanocomposite materials.

Zaradi dobrih mehanskih lastnosti, dobre korozijske odpornosti ter nizke mase je uporaba kompozitov v ladjedelništvu zelo razširjena. Namen te diplomske naloge je bil izdelati cenovno ugoden kompozitni material, z ustreznimi mehanskimi lastnostmi za strehe jadrnic. V ta namen smo izdelali kompozitne plošče iz različnih kombinacij materialov po dveh različnih postopkih izdelave in sicer po postopku infuzije in polaganja v mokrem. Na kompozitnih materialih smo izvedli upogibni preizkus, analizirali mikrostrukturne sestavine ter naredili cenovno analizo. Pri mikrostrukturni analizi smo ugotovili, da so vlakna bolj narazen pri kompozitih narejenih po načinu polaganja v mokrem in da so posamezne plasti bolj narazen pri kompozitih z matico iz epoksi smole. Vsi vzorci so uspešno prestali upogibni preizkus. Vseeno smo ugotovili, da je v kompozitih narejenih z načinom mokrega polaganja nastalo manj napak kot pri kompozitih narejenih z infuzijo. Enako velja za kompozite z armaturo iz ogljikovih vlaken in kompozite z matico iz epoksi smole. Pri cenovni analizi smo ugotovili, da je najcenejša kombinacija materialov kombinacija vinilesterske smole utrjene s steklenimi vlakni. Na podlagi dobljenih rezultatov je bilo določeno, da je od preiskovanih kompozitnih materialov za strehe jadrnic najbolj primeren kompozit z matico iz vinilesterske smole uterjene s steklenimi vlakni, ki je narejen po postopku polaganja v mokrem. Because of their good mechanical properties, good corrosion resistance and their low density the use of composites in boatbuilding is widespread. The purpose of this diploma work was to fabricate a composite material with appropriate mechanical properties for a sailboat hardtop at a satisfactory price. Therefore, the composite plates with different combinations of materials were made, following two different processing routes: infusion and wet lay-up. The samples were subjected to a bend test, their microstructures were analyzed and a cost analysis was made. Microstructural analysis showed that the fibers are more apart in the composites by wet lay-up processing route, and that individual layers are more apart in the composites with epoxy resin as a matrix. None of the samples failed during bend test. Nevertheless, it was seen that the composites made by wet lay-up had less flaws than the composites made by infusion. The same goes for the composites with carbon fibers (reinforcement) and the composites with epoxy resin (matrix). The cost analysis showed that the cheapest combination of materials was a combination of vinylester resin as a matrix and glass fiber as reinforced material. On the basis of the obtained results, it was concluded that the most appropriate composite material for the sailboat hardtop would be the one with vinylester resin matrix reinforced with glass fibers and made by wet lay-up process.

V diplomski nalogi je predstavljeno načrtovanje laminatnega materiala in določevanje materialnih lastnosti. Temo sem si izbral zato, da prikažem del postopka razvijanja šasije pri Formuli Študent. Osrednji področji naloge sta določitev laminacije materiala s pomočjo numerične analize in primerjava med numeričnim in realnim preizkusom na preizkuševalnim stroju. V prvih poglavjih so predstavljeni in opisani pojmi, s katerimi se srečamo v nalogi. Drugi del pa se posveti simulaciji in preizkusom. In my diploma thesis I presented the planning of laminate material and gathering material properties. The theme was chosen to show part of the process of developing chassis at Formula Student. The two main subjects are determination of lamination of the material with the help of numerical analysis and a comparism between the numerical and real test. In the first chapter are represented and described concepts, which we encounter in the assignment. The second part focuses on simulation and test.

V letalski industriji se čedalje bolj uporabljo polimeri, ojačani z ogljikovimi vlakni(CFRP). CFRP kompoziti omogočajo izdelavo kompleksnih oblik, kar bistveno zmanjša število komponent in skupno težo, obenem pa omogočajo večjo trdnost izdelkov v primerjavi s konvencionalnimi materiali. Velika trdnost in heterogenost materiala predstavljata težave pri kontaktnem odrezovanju. Do težav pa prihaja tudi pri brezkontaktnem laserskem preoblikovanju. Epoksidna smola služi kot vezivo karbonskim vlaknom in je delno prosojna tako v vidnem kot v infrardečem spektru, kar povzroča slabo absortivnost laserske svetlobe. Preučili smo osnovne mehanizme laserske ablacije in preizkusili tezo o vmešavanju barvil epoksidni smoli za namene povečanja absorcije laserske svetlobe. S pomočjo podobne literature ter s sistemskim pristopom preizkušanja smo proučili tezo. Uporabili smo večino komercialno dostopnih barvil različnih panog ter tudi nekaj namensko razvitih pigmentov, namenjenih izključno laserskemu označevanju. Ugotovili smo, da barvila nekoliko izboljšajo rezalne lastnosti same epoksidne smole. Na obdelavo CFRP-jev je bistveno bolj kot obarvana epoksidna smola vplivala strategija rezov. Najučinkovitejše je odrezovanje z graviranjem, ki je sestavljeno iz kratkih prehodov rezanja pod kotom +-45◦. Ugotovili smo tudi pomembnost parametra ”prehod vrst”, ki narekuje zaporedje prehajanja vzorca graviranja. Rezultati potrjujejo tezo o povečanju absortivnosti obarvane epoksidne smole. Najpomembnejša ugotovitev je načrtno vodenje laserskega snopa za izboljšane rezalnih lastnosti CFRP materialov. In the aeronautical industry, carbon fibre reinforced polymers (CFRP) are increasingly used. CFRP composites enable the production of complex shapes, which leads to reduced number of required components, lower total weight and enables higher stength of the products comparing to the conventional materials. Great strength and the heterogeneity of the material present problems in contact machining. Problems also occur in non-contact laser processing. The epoxy resin serves as a binder for carbon fibers and is partially transparent in both the visible and the infrared spectrum, causing causing low absorption of laser light. We examined the basic mechanisms of laser ablation and tested the thesis about the dyeing of epoxy resins for the purpose of increasing the absorption of laser light. With the help of existing literature and by a systemativ experimental approach to the experiment, we examined the thesis. We used most of the commercially available dyes of various industries, as well as a few purpose-developed pigments exclusively dedicated to laser marking. We found that the dye slightly improve the cutting characteristics of the epoxy resin itself. Rather dyeing is significantly more important cutting patern. The most effective is engraving cuts, which consists of short cutting crossings at an angle of +- 45◦. We have found the importance of the parameter ''skip line'', which dictates the sequence of transitions of the sample engraving. The results confirm the thesis of increasing the absortiveness of the colored epoxy resin. The most important finding is the systematic management of the laser beam for improved cutting properties of CFRP materials.

Anizotropno trenje ima ključno vlogo pri procesu preoblikovanja polizdelkov iz ogljikovih vlaken. Ta kompleksni pojav otežuje načrtovanje preoblikovalnih orodij in določanje procesnih parametrov. Pri tem si lahko pomagamo s pomočjo numeričnih simulacij na osnovi metode končnih elementov. Da bi natančno napovedali proces preoblikovanja je v simulacijo kontakta med posameznimi plastmi ogljikovih vlaken potrebno vključiti model anizotopnega trenja. V magistrskem delu sta predstavljena dva postopka simuliranja anizotropnega trenja z metodo končnih elementov v programskem okolju Abaqus. Prvi od modelov (M1) je standardno vključen v Abaqus okolje in ponuja eliptično razporeditev tornih sil glede na smer gibanja in usmeritev ploskev. Drugi model (M2) je del uporabniškega podprograma, ki je bil razvit v sodelovanju z razvijalci programa Abaqus in uporablja eksperimentalno določene vrednosti koeficientov trenja, ki jih uporabnik določi v obliki diskretnih vrednosti relativnih usmerjenosti ploskev v kontaktu. Da bi zagotovili pravilno delovanje simulacij je potrebno validirati osnovne modele, ki v simulacijah popisujejo kontakt dveh teles. V ta namen so simulacije v okviru magistrskega dela izvedene na preprostih geometrijah togih teles v obliki ravnih ploskev, ki ne vključujejo materialnih lastnosti. Na ta način zagotovimo opazovanje le kontaktnih modelov brez učinkov mehanskih modelov materiala. Prve simulacije vključujejo le obremenitve v smeri normal ploskev, brez relativnih premikov med ploskvama. Pri teh simulacijah smo opazili napačno razporeditev kontaktnega tlaka, ki se pojavlja pri določenih nastavitvah kontaktnega algoritma. Ker so torne sile neposredno povezane s tlakom na kontaktni površini smo v naslednjem svežnju simulacij ocenjevali vpliv napačne tlačne porazdelitve na ravnovesje sil in momentov v telesih. Opazili smo, da pri določenih nastavitvah prihaja do pojava vrtilnih momentov, ki niso v skladu s teorijo anizotropije trenja ter eksperimentalnimi rezultati. Na podlagi prvih simulacij smo izluščili najbolj primerne nastavitve za simulacijo trenja med dvema ploskvama. Z nadaljnimi simulacijami smo testirali delovanje modela M1 in ocenili zmožnost da popiše anizotropne lastnosti polizdelkov iz ogljikovih vlaken. V ta nemen smo rezultate iz numeričnih simulacij smo primerjali z rezulati eksperimentov trenja med posameznimi plastmi ogljikovih vlaken. Ugotovili smo, da standardni model M1, ki predvideva eliptično porazdelitev tornih sil ne zadošča za modeliranje omenjenih lastnosti zaradi monotonosti eliptične funkcije. Vzporedno smo predstavili zasnovo uporabniškega podprograma (M2) in testirali njegove osnovne funkcije. Ugotovili smo, da v trenutni obliki uporabniški podprogram omogoča natančno simuliranje tornih sil za kombinacije usmeritev materiala in smeri gibanja za katere lahko neposredno določimo koeficiente trenja. Za simuliranje celotnega spektra kombinacij, kjer je potrebna interpolacija med posameznimi vrednostmi koeficientov, pa so potrebna nadaljna testiranja in razvoj algoritma. Rezultat magistrske naloge je uporabniški podprogram, ki predstavlja osnovo za nadaljni razvoj ter omogoča razširitev modela anizotropnega trenja z drugimi parametri v postopku preoblikovanja ogljikovih vlaken kot so na primer temperaturna odvisnost, viskozne in kohezivne lastnosti veziva in hitrost preoblikovanja. Za validiranje takšnega modela so potrebne nove eksperimentalne študije ter razvoj in obsežno testiranje kontaktnega algoritma. Forming of complex carbon fibre preforms predominantely depends on the effects of anisotropic friction. Simulation of the forming process using finite elements method enables succesfull definition of manufacturing proces parameters. Two simulation approaches of anisotropic friction in Abaqus software are presented in the thesis including testing of basic contact interaction models. An existing anisotropic model does not suffice for carbon fibre preforming simulations. Outline and functioning of a user subroutine for anisotropic friction modellling are presented and developed to include basic functionalities.

V okviru projekta Formula Študent smo izdelali šasijo iz kompozitov. Moj cilj je bil, da izdelam smernice za načrtovanje proizvodnje in jih uporabim na mojem primeru. Z lastnimi meritvami sem poiskal koeficiente in bližnjice, ki se lahko uporabijo za lažje načrtovanje. Z zapisanimi enačbami lahko z malo vhodnimi podatki izvemo količine potrebnih materialov in čase izdelave. Z večjo in bolj raznoliko vzorčno skupino bi lahko bile smernice natančneje določene in bi bile univerzalno uporabne v industriji kompozitov. Within the Formula Student project, we created a chassis made of composites. My goal was to make guidelines for production planning and use them on my case. Using my own measurements, I've found coefficients and shortcuts that can be used to make production planning fast and easy. With the equations written, we can find out the quantities of materials and the time of production with a little input data. With a larger and more diversified modeling group, guidelines could be more precise and universally applicable in the composite industry.

Polimerni kompozitni materiali so eni izmed najbolj razširjenih materialov v industriji in v splošni uporabi. V sklopu zaključne naloge bomo merili vpliv različnih tehnoloških postopkov izdelave in orientacije vlaken na splošne mehanske lastnosti materiala ter njihov vpliv na viskoelastične lastnosti smole. Šest različnih polimernih kompozitnih vzorcev ojačanih z ogljikovimi vlakni bomo preizkušali na štiri-točkovnem upogibnem testu. Trije vzorci so bili izdelani po postopku ročne mokre lamincaije z vakuumeranjem ter z [0°]8, [(45°/0°)2]s in [±45°]8 orientacijo vlaken. Drugi trije vzorci pa so bili izdelani po postopku avtoklave s pred-impregniranimi vlakni z isto orientacijo vlaken. Rezultati, pridobljeni z eksperimentalnimi meritvami kažejo, da imata tehnološki postopek izdelave in orientacija vlaken vpliv na mehanske in viskoelastične lastnosti materiala. Polymer composites are one of the most common materials in the use of industry and in everyday use. We measured influence of the orientation of the reinforcement in the composite made by two different technological methods of fabrication. In addition, how this effects viscoelastic behaviour of the material. Six different polymer composite samples reinforced by carbon fibres were studied in the four-point bend test. Three of the samples were made by the process of hand lay-up with vacuum bagging and the [0°]8, [(45°/0°)2]s and [±45°]8 orientation of the fibres. The other three samples were made by the autoclave method with pre-impregnated fibre with the same orientation of the fibres. The results have showed us that the technological methods of fabrication and the orientation of reinforcement have influenced on the mechanical properties of material as well as on viscoelastic behaviour of material.

Onesnaženost pitne vode s pesticidom atrazinom predstavlja kljub prepovedi njegove uporabe v Sloveniji leta 2003, velik problem. Povišane koncentracije atrazina so še vedno zabeležene predvsem v severovzhodnem delu Slovenije, kar je posledica intenzivnega poljedelstva. Namen magistrskega dela je bil preučiti uspešnost adsorpcije atrazina iz pitne vode na vlakna iz 100 % aktivnega oglja. Preučevali smo vpliv temperature in časa na učinkovitost adsorpcije atrazina na vlakna. Preveriti smo želeli, ali z modifikacijo vlaken dosežemo boljšo adsorpcijo. V raziskavi smo meritve višjih koncentracij atrazina (2,5 mg/L) v modelni vodi in pitni vodi določali spektrofotometrično. Nizke koncentracije atrazina (z začetno koncentracijo 1 μg/L) smo določali s plinsko kromatografijo. Učinkovitost adsorpcije atrazina smo interpretirali s pomočjo adsorpcijske kinetike in termodinamike. Rezultati raziskave so pokazali, da se koncentracija atrazina zniža od začetne koncentracije 2,5 mg/L na 0,8 mg/L pri sobni temperaturi in času 60 min. Z naraščanjem temperature se adsorpcija izboljša. Pri 30 °C se koncentracija atrazina zniža na 0,6 mg/L že po 40 min in pri 50 °C po 20 min, kar pomeni da se na vlakna adsorbira 76 % atrazina. Vrednosti ΔG0 so bile negativne, kar pomeni, da je reakcija potekla spontano. Negativne vrednosti ΔS0 dokazujejo, da je vpliv matriksa na vezavo atrazina zanemarljiv. Pri začetni koncentraciji atrazina 1,0 μg/L smo dosegli višje učinkovitosti, kot pri višjih koncentracijah . Na vlakna se je pri 22 °C po 20 min vezalo 90 % atrazina, po 60 min 95 %, in po 300 min 97 %. Adsorpcijo na vlakna iz aktivnega oglja lahko opišemo s kinetičnim modelom pseudo-drugega-reda. Pollution of drinking water with pesticide atrazine represents a large problem, despite the ban on its use in Slovenia since 2003. Elevated concentrations of atrazine are still being monitored, mainly in the north-eastern part of Slovenia as a consequence of intensive farming. The purpose of the master's thesis was to study the efficiency of atrazine adsorption from drinking water using cloth from 100 % activated carbon Zorflex® ACC FM30K. We studied the influence of temperature and time on the efficiency of atrazine adsorption on cloth. The aim was to study the influence of cloth modification on atrazine adsorption. In the research the measurements of atrazine concentrations in model and drinking water were defined spectrophotometrically. Low concentrations of atrazine (with the initial concentration of 1,0 μg/L) were defined with gas chromatography. The efficiency of atrazine adsorption was interpreted by menas of adsorption kinetics and thermodynamics. The results showed that at room temperature the atrazine concentration decreased from the initial concentration of 2,5 mg/L to 0,8 mg/L in 60 min. With increasing the temperature, the adsorption improved. The atrazine concentration decreased to 0,6 mg/L already after 40 min at 30 °C, and to the same concentration after 20 min at 50 °C, thus 76 % of atrazine was adsorbed on the cloth. The values of ΔG0 were negative, which meant that the reaction ran spontaneously. The negative values of ΔS0 proved that the matrix influence on the atrazine binding is negligible. At the initial concentration of 1,0 μg/L higher levels of efficiency were achieved than at higher atrazine concentrations. 90 % of atrazine was bound to the cloth after 20 min at 22 °C, after 60 min 95 %, and after 300 min 97 %. Atrazine adsorption was described by the pseudo-second-order kinetic model.

V diplomskem delu obravnavamo problematiko vpetja ogljikovih vlaken v cementni matrici. Podajamo teoretično ozadje problema ter lastnosti materialov, ki smo jih uporabili v eksperimentalnem delu. Prav tako so navedeni splošni principi izboljšanja vpetja vlaken v cementni matrici. V hipotezi smo predpostavili, da lahko vpetje izboljšamo na dva načina, in sicer z impregniranjem vlaken s cementnim mlekom ter povečanjem trenja na mejni površini z mikro delci mlete odpadne avtomobilske gume. Impregnacija se je pokazala kot dobra rešitev, z mleto gumo pa nismo dosegli pričakovanih rezultatov. In the thesis we address the problem of carbon-fiber yarn bonding into cement matrix. We are presenting theoretical background of the problem and properties of materials we used in experiments. Also, we showed general approaches of bonding improvements in cement matrix. The hypothesis was, there were two ways to improve bonding first one was to impregnate carbon-fiber yarn with cement milk and the second one was friction improvement with microparticles made of waste tyres. Fiber impregnation was a good solution, but samples with rubber particles did not reach expected results.

Magistrsko delo predstavlja konstruiranje samonosne karoserije za dirkalnik Formula Student GPE14. V magistrskem delu so predstavljene omejitve, ki izhajajo iz pravilnika FSAE, položaja preostalih komponent in izbire materiala. Na kratko je predstavljeno modeliranje samonosne karoserije in numerične simulacije, ki smo jih izvedli. Predstavljena sta mehanska preizkusa, ki ju je zaradi pravilnika potrebno izvesti. Prikazano je kako rezultate mehanskih testov uporabimo za prilagoditev numeričnih modelov, da na tak način dobimo iz numeričnih simulacij rezultate, ki so primerljivi z rezultati dejanskih testov. V zadnjem delu magistrskega dela pa je predstavljena izdelava samonosne karoserije. The master’s thesis presents the design of monocoque for Formula Student racing car GPE14. In the master’s thesis the restrictions of the FSAE rules, positions of other racing car components and chosen materials are presented. Briefly the modelling of monocoque and numerical simulations that we preformed is presented. The mechanical tests that were preformed according to the FSAE rules are described as well. It is also shown how we used the results from mechanical tests to adjust the numerical model, so the results of the numerical simulation were closer to the results of the mechanical experiments. In the last part of the master’s thesis the fabrication of the monocoque is shown.

V tem diplomskem delu smo podali ugotovitve eksperimentalne analize obnašanja tlačno obremenjenih betonskih elementov, ki so bili ojačani s CFRP kompoziti. Podani so rezultati tlačnih testov izvedenih na štirih cilindričnih betonskih vzorcih premera 100 mm in višine 150 mm. Predstavljene so mehanske in fizikalne lastnosti FRP materialov, procesi njihove proizvodnje in področja ter zgodovina njihove uporabe v gradbeništvu. In this thesis, we provide findings based on the experimental analysis of the behaviour of concrete elements reinforced with CFRP composites. The results of compressive load tests performed on four cylindrical concrete samples measuring 100 mm in diameter and 150 mm in height are presented. We describe mechanical and physical properties of FRP materials, their manufacturing processes as well as various fields and history of their application in civil engineering.

Uporaba sodobnih materialov in tehnologij gradnje omogoča nov pristop k načrtovanju in oblikovanju objektov. S tem arhitekturo prilagaja sodobnim prostorskim zahtevam in potrebam družbe. Beton, ojačen z ogljikovimi vlakni, je material prihodnosti, ki je ekološko sprejemljiv, trajnosten in arhitektom omogoča svobodo oblikovanja. Magistrsko delo je sinteza reševanja prostorskih problemov z uporabo sodobnih materialov. Ukvarja se s problematiko Maribora in s programsko zasnovo omogoča ekonomsko, gospodarsko in kulturno rast ter razvoj mesta. Maribor je vozlišče in povezovalno središče sosednjih držav. Programska zasnova postavlja mesto v središče regionalnih dogodkov in prireditev. Contemporary materials and building technologies usage, opens a new approach when planning and designing. Architecture is adapted to contemporary spatial requirements and society. Carbon reinforced concrete is material of the future due to sustainability, environmental friendliness and as it gives architects designing freedom. Master thesis synthesizes solving spatial problems with usage of contemporary materials. It is dealing with problems of the city Maribor and with its proposed programme, allows economic and cultural growth and development of the city. Maribor is located in the center of region and is of a great importance in connecting nearby countries. According to the programme, city becomes event center of this region.

V diplomski nalogi je predstavljen problem konstruiranja polosi iz ogljikovih vlaken ter rešitve in prednosti takšne polosi v primerjavi z drugimi materiali. Predstavljene so splošne informacije o ogljikovih vlaknih, različnih razporeditvah vlaken in epoksidni smoli. Prav tako so predstavljeni pomembni napotki, ki jih moramo upoštevati pri konstruiranju polosi za dirkalnik razreda Formule S. V diplomskem delu najdemo tudi informacije o titanovih zlitinah in zlepnih spojih, ki so glavna vez med ogljikovimi vlakni in titanovimi zlitinami. S pomočjo numeričnih analiz, rezultatov že opravljenih raziskav in eksperimentov je prikazan trdnostni preizkus ter življenjska doba polosi. Predstavljena sta tudi preračun ležajev na homokinetičnem zglobu in lastna frekvenca. In this diploma is presented problem of designing carbon fiber axle shaft as well as solution and advantages this kind of axle shaft in comparison with other materials. General informations about carbon fiber-epoxy composite are given. Crucial things while designing axle shaft for Formula Student competition are also presented. In diploma participate also informations about titanium alloys and adhesive joints which are main joints between carbon fiber and titanium alloys. With help of numerical analysis, results of known researches and experiments, strength of axle shaft and fatigue are introduced. Calculations about bearings and natural frequency are also included.

V diplomskem delu smo predstavili lastnosti in karakteristike nekaterih ojačitvenih materialov s poudarkom na ogljikovih vlaknih in CFRP kompozitih ter možnosti njihove uporabe v lesenih konstrukcijah. V eksperimentalnem delu smo opravili natezne in upogibne preizkuse na ojačanih in neojačanih vzorcih različnih dimenzij. Na podlagi rezultatov smo ugotovili, da so vzorci ojačani z ogljikovimi vlakni in CFRP lamelami dosegli večje natezne in upogibne trdnosti ter module elastičnosti v primerjavi z neojačanimi vzorci. Pri ekonomski raziskavi smo s pomočjo vrednostne analize ugotavljali smotrnost uporabe ogljikovih vlaken za ojačitev lesenih konstrukcijskih elementov. Izkazalo se je, da je ojačitev z ogljikovimi vlakni in s CFRP lamelami dosegla nižji rang v primerjavi s povečanim prerezom lesenega elementa, predvsem zaradi relativno visoke cene ogljikovih vlaken. In the thesis we presented the properties and characteristics of some strengthening materials with the focus on carbon fibres and CFRP composites and their possible application in timber structures. In the experimental part, we carried out tension and bending tests on samples of different dimensions with and without strengthening. Based on the experimental results we found that the samples strengthened with carbon fibres and CFRP plates showed greater tension and bending strenghts as well as a greater modulus of elasticity compared to samples without strengthening. We did the economic research with the help of the value analysis on the feasibility of using carbon fibres for strengthening of timber structural elements. The results have shown that strengthening with carbon fibres and CFRP plates achieved a lower rank than enlarging the sectional area of the timber element, manly because of the relatively high cost of carbon fibres.

V diplomskem delu smo obravnavali in primerjali različne metode ojačitve tankih betonskih elementov z ogljikovimi vlakni. V teoretičnem delu smo predstavili lastnosti uporabljenih materialov in opisali različne načine ojačitve betonskih elementov. V eksperimentalnem delu smo opisali postopek priprave vzorcev in izvedbo štiri točkovnega upogibnega preizkusa. Primerjavo rezultatov smo nato izdelali med tremi različnimi načini ojačitve na vzorcih enakih dimenzij in ojačanih z enako količino ogljikovih vlaken. Rezultati preizkusov so pokazali, da zunanje ojačani vzorci dosegajo višje upogibne trdnosti kot vzorci ojačani v sredini prereza. In the diploma thesis, we discuss and compare different methods of thin concrete members reinforcement with carbon fiber. In the theoretical part we present the properties of the materials used and describe the different ways of reinforcing concrete members. In the experimental part we describe the process of preparing samples and implementation of four-point bending test. Comparison of the results was then made between three different models of reinforcement on the samples of the same dimensions and reinforced with the same amount of carbon fiber. The test results showed that the external bonded reinforced members have higher flexural strength than the samples reinforced in the middle of the cross-section.

V diplomski nalogi je predstavljen začetni razvoj kolesa izdelanega iz kompozitnega materiala, ogljikovih vlaken prepojenih z epoksidno smolo, za dirkalnik razreda Formula Student. Predstavljene so splošne informacije o kompozitih z urejenimi kontinuiranimi vlakni v polimerni matrici. V namen numerične simulacije so izdelani linearno elastični materialni modeli treh vrst kompozita iz različnih tkanin ogljikovih vlaken z nateznimi preizkusi. Z numerično analizo je določena razporeditev in orientacija plasti kompozita po kolesu, s kriterijem togosti kolesa. Deloma je določena trdnost kolesa, po kriteriju porušitve plasti Tsa-Hill. Predstavljene so možnosti za nadaljevanje razvoja, do končnega izdelka. In this diploma thesis an initial development phase of Formula Student race car wheel, made out of carbon fiber-epoxy composite is presented. General information on fiber reinforced plastic composites is given. For the purpose of numerical simulations, three linear elastic material models of different carbon fabrics with the same matrix were made with tensile tests. With the numerical analysis the ply layup on the wheel was determined with the use of wheel stiffness requirements. Strength is partially determined with the use of Tsai-Hill ply failure criterion. Possibilities on further development to the final product are presented.

V doktorski disertaciji je obravnavan vpliv dodatkov betonu – mikrosilike, superplastifikatorja in aeranta – na povečanje trdnosti vpetja med cementno malto in pletenico kontinuiranih ogljikovih vlaken. Za preiskavo lastnosti vpetja med pletenico ogljikovih vlaken in različnimi cementnimi maltami so bili uporabljeni rezultati izvlečnih preizkusov, ki smo jih primerjali z rezultati analize mikrostrukture mejnih površin. Eksperimentalni rezultati so potrdili, da je uporaba vseh uporabljenih dodatkov betonu izboljšala kvaliteto vpetja. Najbolj je kvaliteto vpetja med pletenico ogljikovih vlaken in eksperimentalno cementno malto povečala uporaba aeranta. Na podlagi analize rezultatov je bilo ugotovljeno, da lahko zračni mehurčki, ki so posledica delovanja aeranta in so locirani v neposredni bližini zunanjih filamentov pletenice, predstavljajo mehansko oviro, zaradi katere se pri izvleku vlaken občutno poveča trenje na mejni površini. Posledično se povečajo trdnost, togost in žilavost vpetja pletenice ogljikovih vlaken v aerirani malti. V nadaljevanju je v disertaciji prikazana tudi aplikacija novega načina vpetja pletenice ogljikovih vlaken v betonski konstrukciji v primerjavi s klasično rebrasto jekleno armaturo. Po izvedenih upogibnih preizkusih se je izkazalo, da ima vlaknasta armatura številne prednosti pred konvencionalnimi armaturnimi materiali: bistveno stanjšanje prereza (celo do pet krat), majhno maso, možnost poljubnega oblikovanja konstrukcijskih elementov zaradi fleksibilnosti vlaken ter povečano duktilnost in žilavost kompozita. This paper deals with the influence of admixtures – silica fume, superplasticizer and air entraining agent – on the improvement of the bond strength between bundled carbon filaments and cement mortars. Pull-out tests were carried out to examine the bond between carbon-fibre yarn and various cement matrices. An overall microstructural analysis was conducted and correlated with pull-out data. Experimental results showed that all the applied admixtures contributed to improved bonding. The air entraining agent was found to be the most effective in improving the bond strength of the studied carbon-fibre reinforced cement mortar. Air bubbles formed inside the mortar mix as a result of added air entraining agent and the ones formed in the vicinity of the outer filaments of the yarn may provide a mechanical barrier at the interface, leading to a significant increase in interface friction. Additionaly we showed the possibility of using fibrous reinforcement of thin sections compared to a conventional reinforcement with a steel rebars. After carried out bending tests it was proved that the fibrous reinforcement had several advantages over conventional reinforcement materials. The advantages of fiber-reinforced concrete composites are primarily essential thiness of the section (up to five time), low mass, the possibility to arbitrary create elements because of the fiber flexibility and increased ductility and toughness.

V diplomskem delu smo predstavili lastnosti, vrste in tehnologijo proizvodnje aeriranega betona, lastnosti in tehnologijo proizvodnje ogljikovih vlaken, lastnosti in vrste polimernih matric, vpliv mikrovlaken na mehanske lastnosti betonske matrice ter preučili vpliv mikrovalovne energije na betonske mešanice, ogljikova vlakna in polimerne matrice. V okviru eksperimentalnega dela smo predstavili rezultate tlačnih testov ter 4 točkovnega upogiba iz prve faze testiranj. In diploma thesis we presented properties, types, production technology of aerated concrete, production technology of carbon fibers, properties and types of polymer matrices, fiber influence on concrete matrix properties and review the effects of microwave energy on concrete mixtures, carbon fibers and polymer matrices. In the experimental work, we presented results of the compressive strength test and four point deflection test from first phase of testings.

V diplomskem delu je predstavljen vpliv induciranih tlačnih napetosti v cementni matrici na jakost vpetja vlaken, na prenos obremenitve iz matrice na vlakna in na mehanske lastnosti vlaknastega cementnega kompozita med obremenitvijo. Tlačno napetost zaradi krčenja betona smo izmerili s posebej za ta namen razvitim merilcem. Študije smo opravili na vzorcih s cementno malto, v katero smo dodali dodatek aeranta. Med procesom mešanja malte so se kot posledica delovanja aeranta v matrici formirali zračni mehurčki, ki so zaradi povečane poroznosti povzročili precejšnje krčenje cementne matrice in s tem pritiske pravokotno na vlakna. S tem se je povečalo tudi trenje na mejni površini. S pomočjo izvlečnih testov smo na eksperimentalnih preizkušancih v časovnih intervalih izmerili izvlečno silo in opisali vpliv zaradi krčenja povzročenih bočnih pritiskov. Tendenca izmerjenih rezultatov notranjih deformacij se giblje v skladu z navedbami literature. The purpose of present diploma thesis was to describe the impact of induced normal stresses inside the cement matrix on interfacial bond strength, load transfer between fibres and matrix and mechanical properties of fibrous cement composites during loading. Internal compressive stresses due to shrinkage of concrete were measured with the measuring device developed for this purpose. Studies were performed on samples of cement mortar with addition of an air entraining agent. Air bubbles formed inside the mortar mix as a result of added air entraining agent increased porosity and caused substantial shrinkage of cement matrix and subsequent pressure perpendicular to the fibers. This also increased the interfacial friction. Composite bond characteristics were evaluated with conventional pull-out tests. The results of the fibre pull-out tests were then combined with measured and calculated values of shrinkage induced lateral pressure. The results of measurements performed in this study are in accordance with findings of the literature.