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Peter Fajs, 2019, master's thesis

Abstract: The objective of the master thesis is to determine the filling properties of injection moulding process for newly created material, and to understand how the variation of processing parameters affects the flow possibilities. In thesis two materials were analysed, i.e. neat PLA material, which was used as a benchmark material and newly created composite CitrusPLA that is based on biodegradable PLA matrix and reinforced with citrus fibres. To fulfil the aim, the virtual and experimental design of experiment with the Taguchi methodology was conducted with use of spiral flow test, where the flow length of material through mould cavity was observed. The experimental results were the basis for the accuracy validation of numerical results and also to determine the optimum process parameters for injection moulding products with best flow conditions through statistical evaluation. It has been concluded that the newly created composite has lower viscosity compared to benchmark virgin PLA which results in better flow conditions in spiral flow test analysis. Both materials have the same optimal conditions in terms of flow conditions. The contribution of mould temperature is in both cases negligible. However, other two variated parameters i.e. melt temperature and injection speed have higher influence on filling characteristics for both materials.
Keywords: injection moulding optimization, material characterization, Moldflow, injection moulding simulations, Taguchi DOE, bio-composites, citrus waste fibres, PLA
Published in DKUM: 07.06.2019; Views: 1082; Downloads: 9
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Microstructure analysis of internally oxidized Cu-C composite
Rebeka Rudolf, Ladislav Kosec, Alojz Križman, Ivan Anžel, 2006, original scientific article

Abstract: On the basis of experimentally obtained data, it was established that submicron-size bubbles are formed by the internal oxidation of Cu-C composite with fine dispersed graphite particles. They are homogeneously distributed in the Cu-matrix. This process starts with the dissolution of oxygen into the metal at the free surfaces, and continues with the diffusion of oxygen atoms into the volume of copper crystal lattice where they react with the graphite particles. The reactions of dissolved oxygen with carbon yield the gas products (CO2, CO), which cannot be dissolved in the crystal lattice of the matrix. The gas molecules, which are enclosed in the space previously occupied by the graphite, have a greater specific volume than the solid graphite. Consequently, compressive stresses arise in the copper matrix around the bubbles. The interaction of these stress fields with gliding dislocations during loading could improve the mechanical properties of the copper. The internal oxidation kinetic in Cu-C composite depends on the diffusion of oxygen in the copper matrix, and the penetration depth of the internal oxidation front indicates the parabolic nature of the process.
Keywords: metallurgy, Cu-C composites, internal oxidation, bubbles
Published in DKUM: 03.07.2017; Views: 669; Downloads: 85
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Analysis of interface at explosive welded plates from low-carbon steel and titanium
Borut Kosec, Ladislav Kosec, Gabrijela Čevnik, Peter Fajfar, Mirko Gojić, Ivan Anžel, 2004, original scientific article

Abstract: On the basis of experimentally obtained data, it was established that a very thin layer of a melt is generated at the explosive welding of two metals at the bond interface within which impurities flow at the bond during melting. Rapid cooling after the collision generates an alloy of different structure and very small grains of an average thickness app. 1 to 2 micro m. The generation of such an amorphous layer in the bond area has been noticed with various metal combinations and represents a fundamental mechanism of explosive welding of metals. Using the metallographic analysis, the development of the vortices which were formed by the explosive welding of low-carbon steel and titanium plates is described in the paper.
Keywords: metallurgy, explosion welding, plates, composites, low-carbon steel, titanium, melt, vortex
Published in DKUM: 03.07.2017; Views: 917; Downloads: 70
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Metal oxide blended ZSM-5 nanocomposites as ethanol sensors
Madhuri Lakhane, Rajendra S. Khairnar, Megha Mahabole, 2016, original scientific article

Abstract: Nano-ZSM-5 is synthesized without organic template via microwave-assisted hydrothermal technique. The synthesized nano-ZSM-5 zeolite is blended with metal oxides (ZnO and TiO2) to have novel composites as ethanol sensors. The composites are characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) techniques. A study on ethanol sensing behaviour of metal oxide blended composite screen-printed thick films is carried out and the effect of metal oxide concentration on various ethanol sensing features, specifically operating temperature, response/recovery time and active region of the sensor, are investigated. XRD and FTIR confirm the blending of metal oxides in ZSM-5 matrix. Both, ZnO and TiO2 blended, composite films are sensitive to ethanol. It can be concluded that metal oxide blending improves the preformance of sensor for ethanol detection. The response/recovery time and active sensing regions depend upon the concentration of metal oxide in host zeolite. The ZnO/ZSM-5 and TiO2/ZSM-5 composite films are the excellent ethanol sensors.
Keywords: ZSM-5 zeolite, composites, XRD, FTIR, ethanol sensing
Published in DKUM: 26.06.2017; Views: 1137; Downloads: 352
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Monolithic magneto-optical nanocomposites of barium hexaferrite platelets in PMMA
Gregor Ferk, Peter Krajnc, Anton Hamler, Alenka Mertelj, Federico Cebollada, Mihael Drofenik, Darja Lisjak, 2015, original scientific article

Abstract: The incorporation of magnetic barium hexaferrite nanoparticles in a transparent polymer matrix of poly(methyl methacrylate) (PMMA) is reported for the first time. The barium hexaferrite nanoplatelets doped with Sc3+, i.e., BaSc0.5Fe11.5O12 (BaHF), having diameters in the range 20 to 130 nm and thicknesses of approximately 5 nm, are synthesized hydrothermally and stabilized in 1-butanol with dodecylbenzenesulfonic acid. This method enables the preparation of monolithic nanocomposites by admixing the BaHF suspension into a liquid monomer, followed by in-situ, bulk free-radical polymerization. The PMMA retains its transparency for loadings of BaHF nanoparticles up to 0.27 wt.%, meaning that magnetically and optically anisotropic, monolithic nanocomposites can be synthesized when the polymerization is carried out in a magnetic field. The excellent dispersion of the magnetic nanoparticles, coupled with a reasonable control over the magnetic properties achieved in this investigation, is encouraging for the magneto-optical applications of these materials.
Keywords: polymer composites, nanoparticles, polymethyl methacrylate, PMMA
Published in DKUM: 23.06.2017; Views: 980; Downloads: 409
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The influence of thermoplastic elastomers on morphological and mechanical properties of PP/talc composites
Matjaž Denac, Vojko Musil, 1999, original scientific article

Abstract: Recent investigations have shown that modification of polymer matrix with filler and elastomers significantly affects composite's mechanical properties. Isotactic PP modified with either untreated or treated talc and either SEBS or SEBS-gMA were used in these investigations. Samples were prepared by melt-mixing in a Brabender kneading chamber and were compression molded into plates on a laboratory press. The composites were characterised by measuring mechanical properties (Young's modulus, yield stress, notched impact strength) and by defining morphology. Binary sistems PP/talc and PP/elastomer containing up to 16 vol.% of talc and up to 10 vol.% of elastomer, as well as ternary PP/talc/elastomer composites with 12 vol.% talc were investigated. Ternary composite's yield stress was also calculated by semiempirical equations. We have found out, that the use of treated modifiers (talc or elastomer) improves adhesion with matrix, which reflects on mechanical properties as better stress transfer.
Keywords: organic chemistry, polymers, thermoplastics, composites, characterization, chemistry, plastics, elastomers, morphology, mechanical properties
Published in DKUM: 10.07.2015; Views: 1735; Downloads: 64
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The adhesion phenomena in polypropylene/wollastonite composites
Iztok Švab, Vojko Musil, Mirela Leskovac, 2005, original scientific article

Abstract: Modification of polypropylene (PP) with wollastonite fillers was investigated in this paper. Three types of different silane pretreated wollastonite mineral filler were used for preparation of binary PP/wollastonite composites. The composite samples were homogenized in a Brabender Plasti-Corder kneading chamber and compression moulded into plates on a laboratory press. The adhesion between the wollastonite fillers used in this study and the PP matrix was predicted on the basis of the calculated adhesion parameters (work of adhesion, interfacial free energy and spreading coefficient) obtained by the surface free energy of pure materials. The contact angle method was used to determine surface free energy of components. The obtained values of adhesion parameters at the interface in the composites were correlated with mechanical properties as well as morphology observations of corresponding composites and were proved to be in relatively good agreement with the mechanical property measurements. Stronger adhesion in investigated composites has reflected in higher yield stress and tensile strength at break but in lower elongation at break and impact resistance.
Keywords: polypropylene composites, wollastonite, surface energy, adhesion, morphology, mechanical properties
Published in DKUM: 10.07.2015; Views: 1284; Downloads: 92
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Experimental investigation of the stability of particulate dispersoid suspensions in aluminium and magnesium melts
Varužan Kevorkijan, 2000, original scientific article

Abstract: The rejection of Si3N4,Mg3N2, AlN and Si particles from different slurries consisting of molten aluminum and magnesium alloy with 10% of silicon or pure molten metals was experimentally investigated by measuring changes in the electrical resistance of the slurries before and after rejection occurred. In stirring experiments, only individual powder fractions which passed through a 45 µm sieve screen and remained on a 30 µm screenwere applied. The experiments showed that the rejection of Si3N4 particles from Al-10%Si and Mg-10%Si melts occurs when more than 17-18 vol.% of the ceramic phase is dispersed into the melt, while in pure Al and Mg molten metals spontaneous rejection occurs at 7-8 vol.% of the introduced ceramic phase. A similar tendency of rejection (at 16-18 vol.% of particulate in slurry) was also observed during the introduction of silicon particles into Al-10%Si and Mg-10%Si melts.
Keywords: metal matrix composites, particle reinforcement, interface, chemically activated wetting
Published in DKUM: 01.06.2012; Views: 1441; Downloads: 67
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Bond improvement in cementitious mortars reinforced with continuous carbon filaments
Andrej Ivanič, Samo Lubej, Milan Radosavljević, 2009, published scientific conference contribution

Abstract: Among various parameters that influence the properties of the composite, the bond between the cementitious matrix and the fibres is the most important one. This paper investigates the influence of admixtures - silica fume, superplasticizer and air entraining agent - on the improvement of the bond between bundled carbon filaments and cementitious mortars. An overall microstructural analysis has shown that the addition of silica fume strengthen the interfacial transition zone by both the reduction of its porosity and the consumption of CH crystals. The addition of a superplasticizer increased the workability of fresh mortars, but the bond improvement was insignificant. The application of the air entraining agent caused the formation of air bubbles inside the mortar matrix. Air bubbles formed in the vicinity of the multifilament yarn were found to provide mechanical anchoring for fibres leading to a significant increase in interface friction. Fibre-bundle pullout tests were carried out to confirm the effectiveness of the admixtures to improve the interface bonding. Based on the resulting load-displacement curves, air entraining agent was found to be most effective in enhancing the bonding characteristics of the cementitious composite.
Keywords: carbon fibers, cementitious composites, bond properties
Published in DKUM: 31.05.2012; Views: 1218; Downloads: 37
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