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Analysis of noise sources produced by faulty small gear units
Aleš Belšak, Jurij Prezelj, 2007, izvirni znanstveni članek

Opis: Noise source vizualization represents an important tool in the field of technical acoustics. There are many different techniques of noise source visualization. Most of them, however, are intended for a specific noise source in a specific type of acoustic environment. Consequently, a certain visualization method can be used only for certain types of noise sources in a specific acoustic environment and in a restricted frequency area. This paper presents a new visualization method of complex noise sources on the basis of the use of an acoustic camera. A new algorithm has been used, which makes it possible to visualize all types of different complex noise sources. Monopole, dipole or quadropole noise sources can be observed simultaneously. It is possible to track a moving noise source by means of an acoustic camera. In addition to that it is possible to observe various transient acoustical phenomena. Through the use in diagnostics, it is possible to define, by means of noise, the condition of mechanical systems at an advance level.
Ključne besede: gears, failure, noise sources, visualization of noise sources, sound, acoustic analysis, acoustic camera, signal analysis, acoustic image, measurements
Objavljeno: 31.05.2012; Ogledov: 1010; Prenosov: 24
URL Povezava na celotno besedilo

Behaviour of cellular materials under impact loading
Matej Vesenjak, Zoran Ren, Andreas Öchsner, 2008, izvirni znanstveni članek

Opis: The paper describes experimental and computational testing of regular open-cell cellular structures behaviour under impact loading. Open-cell cellular specimens made of aluminium alloy and polymer were experimentally tested under quasi-static and dynamic compressive loading in order to evaluate the failure conditions and the strain rate sensitivity. Additionally, specimens with viscous fillers have been tested to determine the increase of the energy absorption due to filler effects. The tests have shown that brittle behaviour of the cellular structure due to sudden rupture of intercellular walls observed in quasi-static and dynamic tests is reduced by introduction of viscous filler, while at the same time the energy absorption is increased. The influence of fluid filler on open-cell cellular material behaviour under impact loading was further investigated with parametric computational simulations, where fully coupled interaction between the base material and the pore filler was considered. The explicit nonlinear finite element code LS-DYNA was used for this purpose. Different failure criteria were evaluated to simulate the collapsing of intercellular walls and the failure mechanism of cellular structures in general. The new computational models and presented procedures enable determination of the optimal geometric and material parameters of cellular materials with viscous fillers for individual application demands. For example, the cellular structure stiffness and impact energy absorption through controlled deformation can be easily adapted to improve the efficiency of crash absorbers.
Ključne besede: mechanics, porous materials, cellular materials, impact loading, mechanical testing, fluid-structure interaction, failure mechanism
Objavljeno: 31.05.2012; Ogledov: 986; Prenosov: 42
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Upper-bound solutions of three-dimensional passive earth pressures
Stanislav Škrabl, Borut Macuh, 2005, izvirni znanstveni članek

Opis: This paper presents a novel approach to the determination of passive soil pressures: using the upper-bound method within the framework of limit analysistheory. It is based on a three-dimensional, kinematically admissible, rotational, hyperbolical failure mechanism. The failure mechanism is composed of the central and two lateral bodies, which are connected by a common velocity field. This approach is similar to two-dimensional stability analyses, where the log spiral potential failure surface is considered. The front surface of the central body interacts with the retaining wallč the uppersurface can be loaded by surcharge loadingč and the log spiral segment defines the curved failure surface of the central part. The cross sections of the lateral bodies are in agreement with the cross section of the central body. On the outer side, they are laterally bounded by a curved and kinematically admissible hyperbolic surface, which is defined by enveloping the hyperbolical half cones and part of the case surface of the leading half cone. The results give values for the passive soil pressure coefficients that are for most cases lower than the values determined by the upper-bound method of limit analysis for a translational failure mechanism, as published in the literature.
Ključne besede: geomechanics, soil-structure interaction, limit analysis, earth pressures, passive pressure, failure surface
Objavljeno: 01.06.2012; Ogledov: 1070; Prenosov: 65
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The re-characterisation of complex defects
Boštjan Bezenšek, John. W. Hancock, 2004, izvirni znanstveni članek

Opis: The re-characterisation of complex defects with re-entrant sectors has been addressed for cracks extending by fatigue, ductile tearing and cleavage. In Part I crack extension by fatigue and ductile tearing was discussed. In Part II cleavage data are presented for a family of complex defects with re-entrantsectors. Experimental tests on complex and re-characterised profilesare analysed using deterministic and probabilistic approaches. The work addresses the conservatism of re-characterisation procedures when appliedto cleavage failure on the lower shelf and in the ductile-brittle transition.
Ključne besede: fracture mechanics, structural elements, complex defects, recharacterisation, line-spring analysis, cleavage failure, constraint, statistical fracture mechanics, numerical analysis
Objavljeno: 01.06.2012; Ogledov: 667; Prenosov: 59
URL Povezava na celotno besedilo

Application of the european SINTAP procedure to the failure analysis of a broken forklift
Nenad Gubeljak, Uwe Zerbst, Jožef Predan, Maks Oblak, 2004, izvirni znanstveni članek

Opis: The recently developed European flaw assessment procedure SINTAP was applied to the failure analysis of a broken fork of a forklift. Based on the service load at failure, critical crack sizes were determined at different analysis levels of the procedure. It was shown in the present case study that the failure was caused by defective design.
Ključne besede: structural integrity, mechanics of structures, forklift, fracture mechanics, critical crack size, failure analysis, SINTAP procedure, load bearing capacity
Objavljeno: 01.06.2012; Ogledov: 1102; Prenosov: 49
URL Povezava na celotno besedilo

Combination of lung ultrasound (a comet-tail sign) and N-terminal pro-brain natriuretic peptide in differentiating acute heart failure from chronic obstructive pulmonary disease and asthma as cause of acute dyspnea in prehospital emergency setting
Gregor Prosen, Petra Klemen, Matej Strnad, Štefek Grmec, 2011, izvirni znanstveni članek

Opis: Introduction: We studied the diagnostic accuracy of bedside lung ultrasound (the presence of a comet tail sign), N-terminal pro-brain natriuretic peptide (NT-proBNP), and clinical assessment (modified Boston criteria) in differentiating heart failure (HF)- related acute dyspnea from pulmonary (COPD/asthma) related acute dyspnea in the prehospital setting. Methods: Prospective study was performed at the Center for Emergency Medicine Maribor, Slovenia, between July 2007 and April 2010. Two groups of patients were compared: HF-related acute dyspnea group (n = 129) vs pulmonary-related (asthma/COPD) acute dyspnea group (n = 89). All patients underwent lung ultrasound examination, along with basic laboratory, rapid NT-proBNP testing and chest X-ray. Results: Ultrasound comet tail sign has 100% sensitivity, 95% specificity, 100% negative predictive value (NPV) and 96% positive predictive value (PPV) for the diagnosis of HF. NT-proBNP (cut-off point 1000 pg/ml) has 92% sensitivity, 89% specificity, 86% NPV and 90% PPV. Boston modified criteria have 85% sensitivity, 86% specificity, 80% NPV and 90% PPV. Comparing the three methods, we found significant differences between ultrasound sign vs NT-proBNP (P<0.05) and Boston modified criteria (P<0.05). Combination of ultrasound sign and NT-proBNP has 100% sensitivity, 100% specificity, 100% NPV and 100% PPV. With ultrasound we can exclude HF in patients with pulmonary related dyspnea who have positive NT-proBNP (> 1000 pg/ml) and previous history of HF. Conclusions: Ultrasound comet tail sign alone or in combination with NT-proBNP has a high diagnostic accuracy in differentiating between acute HF and COPD/asthma causes of acute dyspnea in prehospital emergency setting.
Ključne besede: lungs, ultrasound, N-terminal pro-brain natriuretic peptide, acute heart failure, chronic obstructive pulmonary disease, asthma, acute dyspnea
Objavljeno: 29.06.2017; Ogledov: 864; Prenosov: 182
.pdf Celotno besedilo (420,76 KB)
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Deformation and energy parameters of fracture of steel of the main gas pipeline
P. O. Maruščak, Sergey Panin, Ulyana Polyvana, Tomaž Vuherer, Anna Guzanová, Janette Brezinová, 2015, izvirni znanstveni članek

Opis: By example of steel 17G1S, the regularities in the impact fracture of Charpy specimens at normal and low temperatures are described. The relationship between the energy parameters of fracture (impact toughness) and the deformation response of the material (the height of shear lips) of the specimens from the pipe steel is established. The micromechanisms of impact fracture of the material are described. At 20 °C and –30 °C, focal splitting of the material was observed on the fracture surface of specimens; at –60 °C, the material failed in a brittle manner by the mechanism of cleavage.
Ključne besede: impact toughness, main gas pipeline, failure analysis
Objavljeno: 08.08.2017; Ogledov: 341; Prenosov: 203
.pdf Celotno besedilo (2,03 MB)
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Analytical and numerical factor of safety (uls) calculations on reinforced embankments
Tadej Vidnar, 2017, magistrsko delo

Opis: This thesis deals with factor of safety calculations on geogrid reinforced embankments carried out by commonly used limit equilibrium (LEM) and finite element methods (FEM). The study utilize LEM based software SLIDE and FEM based software PHASE2. The main difference between these two approaches is that the LEM methods are based on the static of equilibrium whereas FEM methods utilise the stress strain relationship. Unlike to LEM, numerical analysis also computes displacements. For practical example of a geogrid reinforced embankment the factor of safeta (FoS) is calculated. Reinforced soil structures are nowadays utilized for a lot of civil engineering applications. Traditionally, the design of geogrid reinforced soil is performed using analytical methods (LEM). Unfortunately, these methods missing the fundamental physics of stress-strain relationship and are therefore not able to compute a realistic stress distribution. In first step of the analysis the FoS is carried out with analytical approach. The most rigorous LEM methods, Bishop’s, Spencer’s and Morgenstern-Price are selected and the FoS for circular and polygonal slip surface is calculated. In second step of the analysis the FoS is carried out with numerical approach. Shear strength reduction (SSR) procedure was performed to determine the critical strength reduction factor (SRF) which represents the FoS of slope.
Ključne besede: civil engineering, finite element method (FEM), limit equilibrium method (LEM), embankments, slope stability, bearing capacity failure, geosynthetics, geogrids, shear strains
Objavljeno: 27.09.2017; Ogledov: 358; Prenosov: 75
.pdf Celotno besedilo (17,05 MB)

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