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Effect of particle roundness and morphology on the shear failure mechanism of granular soil under strip footing
Babak Karimi Ghalehjough, Suat Akbulut, Semet Çelik, 2018, izvirni znanstveni članek

Opis: This study investigates the effect of particles roundness and morphology on the shear failure mechanism of soil. A strip footing was modeled under laboratory conditions. Calcareous soil was tested with three roundness classes: angular, rounded and well-rounded shapes with sizes of 0.30 mm to 4.75 mm. These were divided into six different groups at three relative densities of 30%, 50% and 70%. A series of photographs was taken during the tests and analyzed using the particle image velocimetry (PIV) method to understand the soil-deformation mechanism. The results showed that increasing the sample sizes increased the affected area of the soil. At the same time, increasing the relative density caused a punching failure mechanism that went towards the general failure. The shear failure mechanism of the soil changed from general toward punching shear failure with increasing particle roundness. This effect was larger with the smaller materials. Underneath the affected layers of soil, the angular samples were deeper than the rounded and well-rounded samples. The affected depth in the angular soil was approximately 1.5B in the smallest size group. This was more than 3B and near 4B in the largest size group. Both the sides and the underlying soil layers should be considered on angular soils. The area under the footing becomes more important than the side parts after increasing the roundness of the particles.
Ključne besede: particle roundness, morphology of particles, shear failure mechanism, strip footing, PIV method, ultimate bearing capacity
Objavljeno: 11.10.2018; Ogledov: 682; Prenosov: 280
.pdf Celotno besedilo (701,47 KB)
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A comparison of the channel geomorphic unit composition of regulated and unregulated reaches in the Soča river
Ian Maddock, Nataša Smolar, Graham Hill, 2007, izvirni znanstveni članek

Opis: This paper examines the effects of flow regulation on the size, spatial distribution and connectivity of channel geomorphic units (CGU) in the Soča River, Slovenia. A river channel survey was completed along three reaches, i.e. an unregulated reach (reach 1), and two regulated reaches with lower discharges, (reach 2 and 3). Results demonstrated significant differences in the CGU composition between the unregulated and regulated reaches. Flow regulation in the Soča River alters the dominant types of CGU's present, significantly reduces the size of CGU's, and affects the longitudinal distribution of types by reducing habitat connectivity and creating greater habitat fragmentation.
Ključne besede: Soča River, river regulation, habitat mapping, channel geomorphic unit, river hydraulics, river morphology
Objavljeno: 05.03.2018; Ogledov: 596; Prenosov: 71
.pdf Celotno besedilo (1,04 MB)
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Making paradigms of verbs and adjectives using a dialect corpus
Chitsuko Fukushima, 2010, izvirni znanstveni članek

Opis: The author has been involved in the making of a dialect dictionary of Tokunoshima, Amami, Japan, using a dialect corpus. The analysis of the dialect corpus and face-to-face interviews were combined to obtain the paradigms of verbs and adjectives to be included in the multimedia dialect dictionary. Sentences in the corpus were cut into phrases and verbs were identified and sorted into lists of verbs. The lists were examined to find patterns of verb conjugation. All conjugated forms were examined regarding succeeding forms, and, based on the distribution, a conjugated form was chosen as an entry. In Japanese, verbs and adjectives belong to the same syntactic category and adjectives change their forms as verbs do. Thus the same procedure was repeated concerning adjectives, and patterns and paradigms of adjective inflection were found.
Ključne besede: Japanese, dialect dictionaries, dialectology, morphology, linguistics
Objavljeno: 05.02.2018; Ogledov: 362; Prenosov: 261
.pdf Celotno besedilo (333,60 KB)
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Experimental testing of single APM spheres
Matej Vesenjak, Lovre Krstulović-Opara, 2010, objavljeni znanstveni prispevek na konferenci

Opis: Advanced pore morphology (APM) foam, consisting of sphere-like metallic foam elements, proves to have advantageous mechanical properties and unique application adjustability. Since the APM foam manufacturing procedure has been developed recently, the mechanical characterization of these materials is still very limited. Therefore, the purpose of this research was to determine the behaviour of APM spheres and its composites when subjected to quasi-staticand dynamic compressive loading. The results of the performed research have shown valuable mechanical properties of the composite APM foam structures, offering new possibilities for their use in general engineering applications.
Ključne besede: advanced pore morphology, foam, composite APM foam structures
Objavljeno: 26.07.2017; Ogledov: 691; Prenosov: 282
.pdf Celotno besedilo (1,61 MB)
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The influence of the morphology of iron powder particles on their compaction in an automatic die
Borivoj Šuštaršič, Matjaž Godec, Črtomir Donik, Irena Paulin, Srečko Glodež, Marko Šori, Milan Ratej, Nada Javornik, 2015, strokovni članek

Opis: Fe- and steel-based powder metallurgy (P/M) products, such as steel gears, spurs, locking mechanisms, porous filters, sliding bearings and bushes, as well as other machine parts and structural elements, are mainly produced with the so-called conventional sintering technology. It is the most efficient technology for the mass production of small, complex, functional and structural parts. Therefore, it is the most convenient and popular among all of the P/M technologies. The most important end-user of sintered parts is the automotive industry. However, small, complex, sintered parts can also be frequently used in the furniture and household industries, precise mechanics, articles for recreation and sports. A fine, iron-based powder mixture or prealloyed powder is first automatically uniaxial-die compacted (ADC) into the final shape of the product with a mechanical or hydraulic press and then sintered in a protective atmosphere at approximately 1100 °C. The metal powder mixture must have the appropriate engineering properties given by the chemistry and particle morphology, enabling a fast and reliable die-compaction process. The most important are a high tap density, a good powder flowability and a low compressibility. All this gives the green compacts an appropriate final shape with a smooth surface, a relatively high and uniform green density, as well as a green strength without internal flaws and cracks. In the case of very small two-or-more-heights products, for example, spur gears with a low module, it is very difficult to obtain a uniform green density at acceptable compaction pressures. Often small cracks are formed at height crossings and big differences in the green density appear in smaller or thinner regions. In the frame of our investigation we analysed the influence of the selected prealloyed commercial iron powder’s morphology and its technological properties on automatic die compaction, as well as the sintering process in the case of small two-level sintered gear dimensions of 5/40–7/10×7mm with module m = 0.5. The original iron powder was sieved and the finest powder particle fraction (< 45 µm) was compared with the original powder mixture considering ADC and sintering process. It was found that the selection of the finer powder mixture could not contribute to the improvement in the overall ADC process, as well as a better green compact. In the present paper the results of our investigations are presented and the reasons why a finer powder mixture cannot contribute much to an improvement of the conventional sintering process.
Ključne besede: Fe-based alloy powders, particles, morphology, microstructure, automatic die compaction, sintering
Objavljeno: 27.03.2017; Ogledov: 635; Prenosov: 275
.pdf Celotno besedilo (1,18 MB)
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Morphological and microstructural features of Al-based alloyed powders for powder-metallurgy applications
Borivoj Šuštaršič, Irena Paulin, Matjaž Godec, Srečko Glodež, Marko Šori, Jože Flašker, Albert Korošec, Stanislav Kores, Goran Abramović, 2014, strokovni članek

Opis: Besides advanced nano steels, polymers and ceramics, recently also light metals, i.e., Al, Mg and Ti based materials, have been recognized as future materials for different kinds of advanced applications. Al and its alloys have an acceptable price, excellent corrosive resistance, good mechanical and other physical properties. Therefore, they are also used in the powder-metallurgy (P/M) field. The P/M technology of Al materials is very demanding and has its own specifics compared to the sintering technology of iron and steel. A relatively large quantity of Al-based alloy powder is formed during the sand blasting of slugs and discs in the Talum Al factory, Kidričevo, Slovenia. Therefore, we analysed and investigated its practical usability for a production of advanced products using P/M technology. The formed Al-based powder was compared with the commercially available Al-based powders that are generally used for conventional sintering technology. In the first part of this paper we explain which types of Al-based powders are used for the production of sintered parts, what the required parameters are and why we considered them. Then, the results of theoretical thermodynamic analyses and investigations of the morphological and microstructural characteristics of the selected commercial Al-based powders are given, as well as their comparison with the Al powder formed during the sand blasting and its potential for P/M applications.
Ključne besede: Al-based alloy powders, morphology, microstructure, LM characterisation, SEM/EDS characterisation
Objavljeno: 17.03.2017; Ogledov: 794; Prenosov: 87
.pdf Celotno besedilo (4,85 MB)
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Computer Modelling of Porous Composite Structures with Advanced Pore Morphology
Aljaž Kovačič, 2016, doktorska disertacija

Opis: Advanced pore morphology (APM) structures are composite metal foams, which are assembled from a large number of small spherical elements with cellular structure, and are bonded into a composite with polymeric adhesive. The result of such composition is a wide spectrum of achievable mechanical behaviour in APM structures. To explore their full potential, efficient computational models are needed, which allow for simple parameter variation. Unfortunately, the current computer models do not allow for efficient simulations of porous composite structures with advanced pore morphology, as they employ complex discretisation approaches. A new approach to simulation is presented in this work, based on the discrete particle method (DPM), where every element of APM structure is discretised with a single node. This enables more efficient simulations of APM structures, while still allowing for simple variation of structural parameters. The DPM method was augmented with constitutive models of normal and tangential contact behaviour of APM elements and bonds between them, which were formulated based on an extensive experimental study of APM structure's geometry and mechanical behaviour. Consequently, the models enable simulations of large APM structure's behaviour by modelling the contact behaviour of individual elements. The implementation of new models was verified on a set of analytically solvable examples, and the accuracy of the models was validated with very good correspondence between computational and experimental results. Moreover, the models were validated on a wide set of examples, also taking into account the various strain rates and the absence of the bonds. The applicability of new models was demonstrated in a comprehensive parametrical study, where the influential structural parameters and properties were identified for low and high strain rate deformations. The study also demonstrated the possibility of customising the mechanical behaviour with property gradation, and with introduction of regular, as well as geometrically complex APM element assemblies. The possibility of coupled discrete particle method and finite element method simulations was also addressed. The newly developed models represent a breakthrough in the field of computational investigation of APM structures, and provide for simpler and more efficient investigations of APM structures in the future.
Ključne besede: Metal foams, advanced pore morphology, composite materials, mechanical properties, contact modelling, discrete particle methods, computer simulations
Objavljeno: 11.03.2016; Ogledov: 1561; Prenosov: 129
.pdf Celotno besedilo (44,29 MB)

Raziskave interakcij med celicami in biopolimernimi materiali z naprednimi eksperimentalnimi metodami kot osnova za študij biokompatibilnosti polimerov
Rok Podlipec, 2015, doktorska disertacija

Opis: The last two decades have been determined by the development in the field of tissue engineering. Beside the constant progress in new biomaterials and scaffold fabrication methods, currently the main focus is to understand scaffolds biocompatibility. In our thesis, physical aspects of scaffold biocompatibility were studied by correlating molecular to macro scale physical properties of scaffolds with cell attachment and cell growth. In order to focus on scaffold physical properties, scaffolds were prepared by the same chemical composition of natural polymer gelatin excluding biochemical effects on the cell response. Scaffold with different physical properties were obtained by changing the temperature, pH and crosslinker degree during the cryogelation and populated by the fibroblast cells. Advanced experimental biophysical methods were applied to determine the polymer mobility via electron paramagnetic resonance (EPR) with spin labelling, the scaffold mechanical properties via rheometry, dynamic mechanical analysis (DMA) and nanoindentation using atomic force microscope (AFM) and the scaffold porosity via confocal fluorescence microscopy (CFM). The anisotropy of the molecular mobility of the side chains of polymers in the crosslinked gelatin structure was found to correlate with the initial cell growth (throughout the first week) the best of all the physical properties measured. About five times less efficient cell growth was measured on the scaffolds with highly mobile, spatially nonrestricted dynamics of the polymer side chains, in comparison with cell growth on the scaffolds with the restricted rotational motion of polymers. The result indicates that cells identify and respond to the degree of polymer mobility, where partially immobile phase is necessary for efficient cell attachment and efficient cell growth. So far, the molecular mobility of polymers constituting tissue engineering materials has never been studied thoroughly with respect to its influence on cell response, and therefore may represent a new experimental approach in understanding biocompatibility. To further understand cell-scaffold interaction, the study focused also on the first events during cell attachment - bond formation between the cell surface proteins and the specific binding sites on the material. In our thesis, cell adhesion dynamics was investigated in real-time on the surfaces of gelatin scaffolds with different physical properties using spatially-controlled cell manipulation by the optical tweezers and the confocal fluorescence microscopy detection. Our goal was to elucidate, if the adhesion dynamics can be correlated with cell growth and if it can be dependent on the scaffold polymer molecular mobility. Quantitative characterization of the optical tweezers force applied during cell-scaffold adhesion analysis was done by viscous drag force calibration and dynamic cell sequential trapping of individual cells. The maximal force on a trapped cell not causing the thermal damage was measured up to 200 pN, with nearly linearly increasing force profile across the cell towards the plasma membrane. By submicron spatial resolution of cell manipulation, we managed to quantify probability of cell adhesion, cell adhesion strength and mechanism of cell attachment, including the formation of the membrane tethers, which slow down the adhesion process. Adhesion strength was classified according to the displacement of the attached cell under the force of optical tweezers measured in the direction of the scaffold surface.Cell adhesion was shown to significantly correlate with cell growth in the first days of culture, while the adhesion itself seems to be dependent on the molecular mobility of surface polymers. The result indicates that the interactions during the first seconds may markedly direct further cell response. The developed methodology for cell adhesion analysis on the surfaces of 3D scaffolds serves as a good tool to forecast scaffold biocompatibility.
Ključne besede: polymer molecular mobility, mechanical response, morphology, scaffold biocompatibility, cell growth, single cell manipulation, cell adhesion dynamics, optical tweezers, electron paramagnetic resonance, dynamical mechanical analysis, nanoindentation, fluorescence microscopy and microspectroscopy
Objavljeno: 06.10.2015; Ogledov: 1446; Prenosov: 96
.pdf Celotno besedilo (5,95 MB)

The influence of thermoplastic elastomers on morphological and mechanical properties of PP/talc composites
Matjaž Denac, Vojko Musil, 1999, izvirni znanstveni članek

Opis: 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.
Ključne besede: organic chemistry, polymers, thermoplastics, composites, characterization, chemistry, plastics, elastomers, morphology, mechanical properties
Objavljeno: 10.07.2015; Ogledov: 1295; Prenosov: 56
.pdf Celotno besedilo (367,27 KB)
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Microvoid system in fibres
Majda Sfiligoj-Smole, Diana Gregor-Svetec, 2002, izvirni znanstveni članek

Opis: The macrovoid system of poly(ethylene terephthalate) (PET) and poly(propylene) (PP) fibres was studied by small-angle x-ray scattering (SAXS). Commercial PET textile fibres were treated in different media and the influence on fibre homogeneity was followd by SAXS. PP technical fibres were manufactured on a laboratory spin-drawing device and subsequently drawn at different drawing conditions on a laboratory drawing device. The influence of drawing on the pore system was followed.
Ključne besede: textile industry, textile fibres, morphology, structure, investigations, SAXS, poly(ethylene terephtalate), PET, poly(propylene), PP, voids, microvoids
Objavljeno: 10.07.2015; Ogledov: 727; Prenosov: 67
.pdf Celotno besedilo (284,24 KB)
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