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The analysis of permanent deformations of repeatedly loaded gravels from the Mura region
Gregor Ficko, Bojan Žlender, 2005, original scientific article

Abstract: This contribution presents the results of the analysis of permanent deformations of gravel in the Mura region under repeated loading. The purpose of the analysis is to forecast the development of permanent normalised axial deformations ▫$/epsilon_1^{p*}$▫ regarding the number of loading cycles N and appurtenant stress states during cycling loading. The analysis used the results of tests performed by ZAG Ljubljana and Faculty of Civil Engineering and Geodesy (FGG) of the University of Ljubljana [1]. The analysis considers five types of stonematerials of different quantity of crushed grains in the mixture and of different water contents. Four types of stone materials are mixtures of different portions of crushed grains larger than 2 mm (Dcr = 87.7 %, 58.9 %, 32.6 % in 0 %), and of the water content around w = wopt - 2%. The stone material with portions of crushed grains larger than 2 mm Dcr= 58.9 % is analysed also for water content w = wopt + 0.7 %. The results of the analysis are deformations expressed as a function of the number of loading cycles N, and a spherical component of the repeated loading p and a distortional component of the repeated loading q. The results can be presentedas deformation surfaces in the ▫$/epsilon_1^{p*}$▫ - p - q space for an arbitrary number of cycles N. The relation between the spherical stress component p and the distortional stress component q, at arbitrary values of axial permanent deformations ▫$/epsilon_1^{p*}$▫, gives a failure envelope, and the so called deformation envelopes in the p - q space. The failure envelopes and deformation envelopes are given separately for five types of stone material. The deformation envelopes are low at small values of the axial permanent deformation ▫$/epsilon_1^{p*}$▫ When permanent axial deformations grow, the permanent deformation approaches the failure envelopes. The failure envelopes for individual types of stone material agree with research results performed by [1]. The analysis of permanent deformations also shows their dependence on the portion of crushed material Dcr in the mixture of crushed and uncrushed stone material. The deformation envelope for uncrushed stone material is situated in the lowest position, regarding the portion of crushed material in the mixture. With an increased portion of crushed material in the mixture of crushed and uncrushed stone material, the deformation envelope is also higher, similarly to the lawfulness of failure envelopes. The relation of failure and deformation envelopes is mathematically established as a function of the portion of crushed grains larger than 2 mm. The comparison of stone material results for different water contents shows that a minimal increase of water content above the optimal one essentially increases deformation.
Keywords: building materials, Mura river gravel, cyclic triaxial tests, granular base material, permanent deformation, normalized axial permanent deformation
Published: 01.06.2012; Views: 983; Downloads: 23
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Crack tip shielding or anti-shielding due to smooth and discontinuous material inhomogeneities
N.K. Simha, Franz Dieter Fischer, Otmar Kolednik, Jožef Predan, G.X. Shan, 2005, original scientific article

Abstract: This paper describes a theoretical model and related computational methods forexamining the influence of inhomogeneous material properties on the crack driving force in elastic and elastic-plastic materials. Following the configurational forces approach, the crack tip shielding or anti-shielding dueto smooth (e.g. graded layer) and discontinuous (e.g. bimaterial interface)distributions in material properties are derived. Computational post-processing methods are described to evaluate these inhomogeneity effects.The utility of the theoretical model and computational methods is demonstrated by examining a bimaterial interface perpendicular to a crack in elastic and elastic-plastic compact tension specimens.
Keywords: fracture mechanics, fracture toughness, composite materials, layered material, inhomogeneity, cracks, finite element method, elastic bimaterials
Published: 01.06.2012; Views: 1079; Downloads: 45
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Phenols, proanthocyanidins, flavones and flavonols in some plant materials and their antioxidant activities
Mojca Škerget, Petra Kotnik, Majda Hadolin Kolar, Andreja Rižner Hraš, Marjana Simonič, Željko Knez, 2005, original scientific article

Abstract: Methanol extracts prepared from five plant materials native to the Mediterranean area, namely olive tree (Olea europaea) leaf, St. John's wort (Hypericum perforatum), hawthorn (Crataegus laevigata), oregano (Origanum vulgare) and laurel leaf (Lauris nobilis), were examined for their phenolic components. Total phenolic content was determined by the Folin-Ciocalteu method. The content of proanthocyanidins in acid-hydrolysed extracts was determined spectrophotometrically. The contents of free flavones (apigenin andluteolin) and flavonols (kaempferol, myricetin and quercetin) were determined by HPLC analysis. The time of hydrolysis of flavones, flavonols andproanthocyanidins was optimised. Antioxidant activities of apigenin, luteolin, kaempferol, myricetin, quercetin and of plant extracts were examined. Antioxidative activities were studied in sunflower oil at 98 °C, by measuring peroxide value, and in an aqueous emulsion system of -carotene and linoleic acid by measuring the absorbance of the sample. Among flavones and flavonols investigated, only myricetin inhibited oxidation of sunflower oil. All other flavones and flavonols showed pro-oxidative activity. Oppositely, in the emulsion system, only apigenin showed pro-oxidative activity while otherflavones and flavonols and plant extracts inhibited oxidation of -carotene.
Keywords: chemical processing, extraction, plant material, fenolic content, hidrolysis, antioxidants, flavones, flavonols, proanthocyanidines, oils, emulsions
Published: 01.06.2012; Views: 1318; Downloads: 61
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On fracture behaviour of inhomogeneous materials - a case study for elastically inhomogeneous bimaterials
Otmar Kolednik, Jožef Predan, G.X. Shan, N.K. Simha, Franz Dieter Fischer, 2005, original scientific article

Abstract: This paper presents a case study, examining the influence of a sharp bimaterial interface on the effective crack driving force in a fracture mechanics specimen. The inhomogeneity of the elastic modulus in linear elasticand non-hardening and hardening elastic-plastic bimaterials is considered. The interface is perpendicular to the crack plane. The material properties and the distance between the crack tip and the interface are systematically varied. The effect of the material inhomogeneity is captured in form of a quantity called "material inhomogeneity term",▫$C_inh$▫. This term can be evaluated either by a simple post-processing procedure, following a conventional finite element stress analysis, or by computing the J-integral along a contour around the interface, ▫$J_int$▫. The effective crack driving force,▫$J_tip$▫, can be determined as the sum of ▫$C_inh$▫ and the nominally applied far-field crack driving force, ▫$J_far$▫. The results show that ▫$C_inh$▫ can be accurately determined by both methods even in cases where ▫$J_tip$▫-values are inaccurate. When a crack approaches a stiff/compliant interface,▫$C_inh$▫ is positive and ▫$J_tip$▫ becomes larger than ▫$J-far$▫. A compliant/stiff transition leads to a negative ▫$C_inh$▫, and ▫J_tip$▫ becomes smaller than ▫$J_far$▫. The material inhomogeneity term, ▫$C_inh$▫, can have the same order of magnitude as ▫$J_far$▫. Based on the numerical results, the dependencies of ▫$C_inh$▫ on the material parameters and the geometry are derived. Simple expressions are obtained to estimate ▫$C_inh$▫.
Keywords: mechanics of structures, fracture toughness, inhomogeneous materials, J-integral, crack driving force, interface, material force
Published: 01.06.2012; Views: 776; Downloads: 9
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Computer-aided analysis of the forging process
Matjaž Šraml, Janez Stupan, Iztok Potrč, Janez Kramberger, 2004, original scientific article

Abstract: This paper presents computer simulation of the forging process using the finite volume method (FVM). The process of forging is highly non-linear, where both large deformations and continuously changing boundary conditions occur. In most practical cases, the initial billet shape is relatively simple, but the final shape of the end product is often geometrically complex, to the extent that it is commonly obtained using multiple forming stages. Examples of the numerical simulation of the forged pieces provided were created using Msc/SuperForge computer code. The main results of the analysis are deformed shape, temperature, pressure, effective plastic strain, effective stress and forces acting on the die.
Keywords: forging, computer simulation, finite volume method, deformation, stresses, material flow, industrial applications
Published: 01.06.2012; Views: 1013; Downloads: 52
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Sandi Bukovšek, 2012, undergraduate thesis

Abstract: Porozne polimerne materiale, ki jih pripravljamo iz emulzij, ki vsebujejo visok delež notranje faze, imenujemo poliHIPE materiali. Zaradi odprte celične strukture so visoko porozni (tudi do 99 %). Uporabni so na različnih področjih, kjer rabimo veliko površino, glede na malo maso materiala, kot npr. pri filtrih za razna filtriranja, za molekularne separacije in sinteze ali kot nosilce v katalizi in v biotkivnem inženiringu. Predmet mojega diplomskega dela je bila priprava bikontinuirnih poroznih polimerov na osnovi poli(stirenov) in poli(N-izopropilakrilamida). Monomeri so bili prisotni v organski kot v vodni fazi emulzij. PoliHIPE materiali so v organski fazi vsebovali monomer stiren in zamreževalec divinilbenzen, ki sta tvorila hidrofoben skelet. Odprto strukturo celic materiala smo napolnili s hidrofilnim gelom iz poli-NIPAAm-a, ki smo ga zamrežili z MBA. Tako pripravljene bikontinuirne porozne polimere smo testirali s pretokom raztopine skozi monolitni material. Ker je poli-NIPAAm temperaturno odziven material, se je le-ta ob spremembi temperature pretočnega medija odzval. Odziv je bil nabrekanje ali skrčenje materiala v notranjosti por, kar je vplivalo na pretok raztopine in pritisk v koloni. Z vrstično elektronsko mikroskopijo smo določili morfologijo monolitnih materialov in s tem potrdili njihovo poroznost. Z infrardečo spektroskopijo smo preverili kemijsko strukturo monolitov. Monolitom smo izmerili povratni tlak s pomočjo HPLC črpalke.
Keywords: monolit, emulzija z visokim deležem notranje faze, stiren, DVB, polimerizacija, porozen material, poliHIPE, N-izopropilakrilamid, poli-NIPAAm
Published: 11.09.2012; Views: 1700; Downloads: 138
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Romana Turner, 2012, undergraduate thesis

Abstract: Da je proizvodno podjetje lahko uspešno, mora zagotavljati zadostne količine materiala za nemoteno proizvodnjo vendar pa je tukaj potrebno ogromno znanja s področja skladiščnega poslovanja. Glede na materiale, katere podjetje potrebuje za svoje delovanje, se odločamo o izvedbi skladiščnih prostorov. Kolikšne bodo zaloge in ali bomo skladiščne prostore najeli ali bomo skladiščili sami je odvisno od več dejavnikov, predvsem pa od višine stroškov, katere nam povzročajo zaloge. Kako bomo knjižno zavedli prejem blaga in nato izdajo blaga je odvisno od politike poslovanja podjetja. Nikakor ne smemo pozabiti pri prejemu blaga, da je potrebno izvesti razne kontrole od ustreznosti blaga do same kvalitete blaga. SGA izdajo vrši po principu FIFO. Z avtomatizacijo skladišč se je mogoče izogniti marsikateri napaki človeškega faktorja, saj se večina knjižnih premikov preko odčitavanja črtnih kod avtomatsko zavede v sistemu. Prav tako z regalnim avtomatskim skladiščem pridobimo na samem skladiščnem prostoru. Inventura ob končanem poslovnem obdobju je izraz našega dela skozi obdobje in vsa odstopanja v zalogah nam prikazujejo kolikšne so bile napake pri manipuliranju z blagom.
Keywords: proizvodno podjetje, material, skladiščno poslovanje, skladiščni prostor, strošek, zaloga, kvaliteta blaga, FIFO, regalno avtomatsko skladišče, inventura
Published: 14.11.2012; Views: 2045; Downloads: 268
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Konstruiranje naprave za merjenje lastnosti sipkega materiala
Gregor Blagotinšek, 2012, undergraduate thesis

Abstract: Na podlagi zahtev, je bilo potrebno skonstruirati napravo, ki omogoča merjenje nasipnega kota različnih materialov na različnih podlagah. Podjetje za katerega se je izdelovala naprava, se sooča s težavo določanja naklona polžnih transporterjev, zato v ta namen za natančnejše določanje parametrov potrebujejo omenjeno napravo. Konstruiranje naprave je potekalo s pomočjo programa CREO v katerem je med drugim potekala izdelava tehniške dokumentacije in analiza obremenitev najbolj izpostavljenih delov. Sama konstrukcija naprave je sestavljena iz standardnih profilov in ostalih standardnih stojnih elementov.
Keywords: Strojništvo, konstrukcije, dimenzioniranje, naprave, nasipni kot, sipki material
Published: 15.11.2012; Views: 1232; Downloads: 178
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Metka Arih, 2012, undergraduate thesis

Abstract: Problem, s katerim se, tako kot tudi večina vseh podjetij, sooča podjetje X, je kako zmanjšati stroške poslovanja na najmanjši možni nivo, da bo poslovanje čim bolj dobičkonosno. Možnost, da bi povečan dobiček dosegli z dvigom cen, zaradi trenutne svetovne gospodarske situacije ter vse večje konkurence, ni realistična. V diplomski nalogi je narejena analiza stroškov podjetja X, s poudarkom na stroških proizvodnje. V nalogi so na podlagi zbranih podatkov razvidni trendi gibanja stroškov ter odvisnosti stroškov od obsega poslovanja. Največja stroška podjetja X sta material in delo. Glede na postavljene cilje podjetja, predračunani dobiček podjetja za tekoče leto, so podani predlogi oz. ukrepi, kako ob planiranem poslovanju doseči takšen nivo stroškov, da bo predračunani dobiček tudi ustvarjen. Ob tem se je potrebno zavedati, da dosledno zmanjševanje določenih stroškov lahko kratkoročno ali dolgoročno te stroške ali z njimi povezane stroške še poveča oziroma celo ogrozi poslovanje (npr. cenejši material - slabša kvaliteta, zmanjševanje plač – izguba dobrih kadrov ipd.)
Keywords: proizvodnja, stroški, material, delo, analiza
Published: 31.01.2013; Views: 3279; Downloads: 304
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