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Quasi-distributed long-gauge fiber optic sensor system
Matjaž Linec, Denis Ðonlagić, 2009, izvirni znanstveni članek

Opis: This paper presents a quasi-distributed, long-gauge, sensor system for measurement optical path length variation. This system can be directly applied to long gauge strain and/or temperature sensing. The proposed sensor system is comprised of sensing fiber, which is divided into the sensorćs segments separated by semi reflective mirrors made out of standard optical connectors. Short duration radio-frequency modulated optical bursts are launched into the sensing fiber and phase differences among individual reflected bursts are measured to determine the optical path-length variations among neighboring mirrors. Twenty sensing fiber segments were successfully addressed by a single-signal processor, while relying on standard telecommunication PIN diode, and a Fabry Perot laser diode. The resolution of a fiber-length variation better than 5 ìm was demonstrated in practice. Since the long sections of fiber can be employed for constructing individual sensors within the sensor's array, a microstrain resolution can be achieved in practice. The drift of the sensorćs system can be predominantly attributed to the temperature sensitivity of the electronic components, which proved to be below 20 um/°C. The entire system relies on simple and widely-used components that are low-cost.
Ključne besede: fiber optic systems, fiber optics sensors, sensing fiber, long-gauge, strain sensing, temperature sensing, optoelectronics
Objavljeno: 31.05.2012; Ogledov: 844; Prenosov: 4
URL Polno besedilo (0,00 KB)

Modelling of surface crack growth under lubricated rolling-sliding contact loading
Boštjan Zafošnik, Zoran Ren, Jože Flašker, Gennady Mishuris, 2005, izvirni znanstveni članek

Opis: The paper describes modelling approach to computational simulation of surface crack growth subjected to lubricated rolling-sliding contact conditions. The model considers the size and orientation of the initial crack, normal and tangential loading due to rolling-sliding contact and the influence of fluid trapped inside the crack by a hydraulic pressure mechanism. The motion of the contact sliding load is simulated with different load cases. The strain energy density (SED) and maximum tangential stress (MTS) crack propagation criteria are modified to account for the influence of internal pressure along the crack surfaces due to trapped fluid. The developed model is used to simulate surface crack growth on a gear tooth flank, which has been also experimentally tested. It is shown that the crack growth path, determined with modified crack propagation criteria, is more accurately predicted than by using the criteria in its classical form.
Ključne besede: fracture mechanics, numerical methods, contact loading, finite element analysis, internal pressure, maximum tangential stress, strain energy density, surface crack growth
Objavljeno: 01.06.2012; Ogledov: 1200; Prenosov: 6
URL Polno besedilo (0,00 KB)

Critical plane modelling of fatigue initiation under rolling and sliding contact
Matjaž Šraml, Jože Flašker, Iztok Potrč, 2004, izvirni znanstveni članek

Opis: Contact fatigue is a phenomenon of important practical significance for engineering applications involving localized contacts, such as gears, rail wheel system and rolling bearings. The service lifetime of such components is related to damage, which results from the contact fatigue. The process in the material structure that causes this kind of failure is quite complicated. The aim of the present paper is to describe a contact fatigue initiation criterion, based on the critical plane approach for the general contact problem. On the basis of contact stress analysis with modified Hertzian boundary conditions, the loading cycle of characteristic material points in the contact area is determined. The Dang Van damage initiation criterion is based on the critical plane approach, which combines the largest allowable shearing and hydrostatic stresses (tensile and compressive), with an assumed elastic shakedown behaviour and it is used in this work. The material point of initial fatigue damage is then determined at the transition of the loading cycle stresses over the critical plane. The model assumed a homogeneous and elastic material model, without any imperfections or residual stresses, and elastic shakedown is considered. A proper determination of loading cycles and their characteristic values is of significance for contact fatigue initiation analysis. Finally, determination of the most critical material point on or under the contact surface and related number of loading cycles required for fatigue damage initiation is calculated with the strain-life (▫$epsilon$▫-N) method.
Ključne besede: machine elements, contact fatigue, crack initiation, strain life method, critical plane approach, numerical modeling
Objavljeno: 01.06.2012; Ogledov: 728; Prenosov: 2
URL Polno besedilo (0,00 KB)

Evaluation of stress intensity factors using finite elements
Boštjan Zafošnik, Zoran Ren, Miran Ulbin, Jože Flašker, 2002, objavljeni znanstveni prispevek na konferenci

Opis: The paper describes a suitability of Virtual Crack Extension (VCE) method for numerical simulation of crack propagation under mixed mode loading. The suitability of VCE method was determined using The Compact-Tension-Shear (CTS), which is subjected to fracture Mode I, Mode II or mixed mode (Mode I + Mode II) loading. In mixed mode the crack kinks when fracture crack growth occurs. Kink angle is determined with VCE method, which is an energy method, maximum tangential stress (MTS) criterion, strain energy density (SED) criterion and experimental results. Determination of crack propagation angle using MTS and SED criterion is based in regard to the stress intensity factors KI and KII. Stress intensity factors are determined using the maximum energy release rate theory using complex J integral, crack opening displacement method and method of stresses extrapolation. Bigger is the rate between KII and KI, crack path, determined with VCE method, propagates more slowly to the kink angle, determined with experiment. The computational results show that the VCE method is suitable for crack propagation, when KI around the crack tip is dominant. In case where KII is dominant, crack does not kink immediately as in other two criteria. When KII dominates around a crack tip, MTS criterion is the most appropriate for determination of kink angle.
Ključne besede: fracture mechanics, stress intensity factors, CTS specimen, crack propagation, virtual crack extension method, strain energy density criterion, maximum tangential stress criterion
Objavljeno: 01.06.2012; Ogledov: 1234; Prenosov: 1
URL Polno besedilo (0,00 KB)

Dynamic property of aluminium foam
Seiichi Irie, Toshihiko Okano, Shigeru Tanaka, Shigeru Itoh, Kazuyuki Hokamoto, Matej Vesenjak, Zoran Ren, 2010, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: aluminium foam, powder gun, high strain rate
Objavljeno: 10.07.2015; Ogledov: 362; Prenosov: 0
URL Polno besedilo (0,00 KB)

Strains and stresses of workers caused by exposure to noise
Simona Jevšnik, Andrej Polajnar, Nataša Vujica-Herzog, Borut Buchmeister, 2012, izvirni znanstveni članek

Opis: This paper examines basic aspects of determining strain due to noise on workers in an industrial environment. Technological development enables better working conditions which then demands changes in methods for measuring strain and stress loadings. A modified method is now presented since the existing method for determining strains caused by exposure to noise is proving insufficient. The objective of the modified method is to eliminate the shortcomings of the existing method by taking into account the complex effects of noise in specific working environments. The effects of exposure to noise will be assessed by using a new strain-assessment procedure which incorporates the effects of nature of noise, characteristics of noise, current standards on protection from noise, and the influence of noise on different jobs. This new noise-assessment approach uses new measurement techniques based on tonality and impulsive noise corrections. The modified method has been tested at various workplaces in the metal-working industry. A comparison of the results obtained by using both methods confirms the suitability of the modified method, thus providing a more complete approach to evaluating strain due to noise.
Ključne besede: ergonomija, hrup na delovnem mestu, strain, stresses, ergonomic coefficient, noise, impulsive noise correction, tone correction
Objavljeno: 10.07.2015; Ogledov: 243; Prenosov: 3
URL Polno besedilo (0,00 KB)

Deflection of polymer gear tooth under static load using numerical analysis
Nina Hanžič, Jože Flašker, Boštjan Zafošnik, 2013, objavljeni znanstveni prispevek na konferenci

Ključne besede: polymer gears, stree strain, Young's modulus, gear tooth root
Objavljeno: 10.07.2015; Ogledov: 120; Prenosov: 1
URL Polno besedilo (0,00 KB)

Vertical displacements measuring methods during bridge load tests
Boštjan Kovačič, Ante Marendić, Rok Kamnik, Mikhail Volkov, Vera Roy, 2016, objavljeni znanstveni prispevek na konferenci

Opis: This article introduces the use of the GNSS method for the load testings of bridge structures. We know that there area lot of methods by which you can determine vertical displacement. However, as new bridge constructions are constructed over almost impossible and inaccessible gorges and valleys, the classic measurements method do not allow us to determine vertical displacement so reliably any more or they are very time-consuming. The GNSS method is well known but there are difficulties when determining the altitude component of this method, which is rather questionable. For this purpose, the methods were tested as practical examples in which some difficulties were encountered, so subsequently another test recording was performed of altitude changes using this method.
Ključne besede: bridges, measurements, strain gauge, load test, deformation, strain, signal processing
Objavljeno: 29.08.2016; Ogledov: 261; Prenosov: 7
.pdf Polno besedilo (1,55 MB)

International Clostridium difficile animal strain collection and large diversity of animal associated strains
Sandra Janežič, Valerija Tkalec, Bart Pardon, Alexander Indra, Branko Kokotovic, Jose Luis Blanco, Christian Seyboldt, Rodriguez Diaz, Ian Poxton, Vincent Perreten, Ilenia Drigo, Alena Jiraskova, Matjaž Ocepek, Scott Weese, Glenn Songer, Mark Wilcox, Maja Rupnik, 2014, izvirni znanstveni članek

Opis: Background: Clostridium difficile is an important cause of intestinal infections in some animal species and animals might be a reservoir for community associated human infections. Here we describe a collection of animal associated C. difficile strains from 12 countries based on inclusion criteria of one strain (PCR ribotype) per animal species per laboratory. Results: Altogether 112 isolates were collected and distributed into 38 PCR ribotypes with agarose based approach and 50 PCR ribotypes with sequencer based approach. Four PCR ribotypes were most prevalent in terms of number of isolates as well as in terms of number of different host species: 078 (14.3% of isolates; 4 hosts), 014/020 (11.6%; 8 hosts); 002 (5.4%; 4 hosts) and 012 (5.4%; 5 hosts). Two animal hosts were best represented; cattle with 31 isolates (20 PCR ribotypes; 7 countries) and pigs with 31 isolates (16 PCR ribotypes; 10 countries). Conclusions: This results show that although PCR ribotype 078 is often reported as the major animal C. difficile type, especially in pigs, the variability of strains in pigs and other animal hosts is substantial. Most common human PCR ribotypes (014/020 and 002) are also among most prevalent animal associated C. difficile strains worldwide. The widespread dissemination of toxigenic C. difficile and the considerable overlap in strain distribution between species furthers concerns about interspecies, including zoonotic, transmission of this critically important pathogen.
Ključne besede: Clostridium difficile, animals, ribotyping, geographic distribution, strain collection
Objavljeno: 29.06.2017; Ogledov: 35; Prenosov: 1
.pdf Polno besedilo (985,16 KB)

Typing Clostridium difficile strains based on tandem repeat sequences
N Henning Zaiß, Maja Rupnik, Ed J Kuijper, Celine Harmanus, Dolf Michielsen, Koen Janssens, Ulrich Nübel, 2009, izvirni znanstveni članek

Opis: Background: Genotyping of epidemic Clostridium difficile strains is necessary to track their emergence and spread. Portability of genotyping data is desirable to facilitate inter-laboratory comparisons and epidemiological studies. Results: This report presents results from a systematic screen for variation in repetitive DNA in the genome of C. difficile. We describe two tandem repeat loci, designated 'TR6' and 'TR10', which display extensive sequence variation that may be useful for sequence-based strain typing. Based on an investigation of 154 C. difficile isolates comprising 75 ribotypes, tandem repeat sequencing demonstrated excellent concordance with widely used PCR ribotyping and equal discriminatory power. Moreover, tandem repeat sequences enabled the reconstruction of the isolates' largely clonal population structure and evolutionary history. Conclusion: We conclude that sequence analysis of the two repetitive loci introduced here may be highly useful for routine typing of C. difficile. Tandem repeat sequence typing resolves phylogenetic diversity to a level equivalent to PCR ribotypes. DNA sequences may be stored in databases accessible over the internet, obviating the need for the exchange of reference strains.
Ključne besede: Clostridium difficile, microbiology, strain typing
Objavljeno: 29.06.2017; Ogledov: 33; Prenosov: 1
.pdf Polno besedilo (792,24 KB)

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