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An approach to consider the arterial residual stresses in modelling of a patient-specific artery
Janez Urevc, Miroslav Halilovič, Milan Brumen, Boris Štok, 2016, original scientific article

Abstract: In this work, the residual stress state of a human common carotid artery is predicted using the so-called thermomecha- nical analogy approach. The purpose of the approach is to enable consistent mapping of residual stresses and the respec- tive configuration from a circular arterial segment to a patient-specific arterial geometry. This is achieved by applying proper volumetric dilatations to the actual arterial stress-free in vivo geometry, which makes use of the analogy that states that the bending stresses can be obtained on an equivalent manner by applying proper thermal dilatations. The common carotid artery data are obtained in vivo from a healthy 28-year-old man using non-invasive methods. The pre- dicted residual stresses of the common carotid artery are in good quantitative agreement with the data from prior work in this field. The approach is validated by predicting the common carotid artery zero-stress state configuration, where a sector-like (cut-open) state is obtained. With this approach, it is thus possible to predict the residual stresses as well as the configuration of patient-specific arterial geometry without the need to model its cut-open zero-stress configuration.
Keywords: patient-specific artery, common carotid artery, residual stresses, arterial zero-stress state, thermomechanics, finite element method
Published: 12.07.2017; Views: 652; Downloads: 277
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Fatigue crack initiation from microstructurally small Vickers indentations
Tomaž Vuherer, Andrej Godina, Zijah Burzić, Vladimir Gliha, 2007, original scientific article

Abstract: The resistivity of coarse grain steel against crack initiation in the presence of micro defects is discussed. Samples of material with martensitic microstructure were prepared by adequate thermal treatment. Microstructurally small Vickers indentations were used as an artificial micro defect. The compressive residual stresses are due to the irreversibility of plastic deformation. The moment of indenting enables to prepare samples with and without effects of residual stresses. The stress level for crack initiation depends on the actual indentation size. The location of initiated cracks is affected by the presence and character of residual stresses.
Keywords: welded joints, micro defect, coarse grain HAZ, crack initiation, crack growth, stress concentration, fatigue limit, Vickers, residual stresses
Published: 03.07.2017; Views: 608; Downloads: 82
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Measurement of strain caused by residual stresses in a welded joint using neutron diffraction
Nenad Gubeljak, Jelena Vojvodič-Tuma, Hans-Georg Preismeyer, 1999, original scientific article

Abstract: The distribution and amount of residual stresses can significantly contrubute to the fatigue fracture behaviour of welded joints in structures. Interior residual stresses, which interact with the plane strain state, are more dangerous than residual stresses at the surface of the welded joint. If the surface of the welded joint is mechanically treated (e.g. shapering), then significant differences between the stress stated at the surface and within the volume occur. Hence, different non-destructive methods (e.g. gamma radiation, neutron diffraction) have been developed to determine strains caused by residual stresses in the volume of polycrystalline materials. However, the measurement of strains caused by residual stresses becomes difficult for large samples. In this paper the measurement procedure on a sample taken from the weld joint is presented and the effecet of residual stresses on fatigue crack propagation is assessed for low and high cycle loading fatigue.
Keywords: zaostale napetosti, zvarni spoj, neutronski lom žarkov, utrujenostno širjenje razpoke, neutron diffraction method, residual stresses, fatigue crack propagation, weld joint
Published: 10.07.2015; Views: 657; Downloads: 16
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Role of residual stresses on fracture properties of under-matched butt weld
Inoslav Rak, Vladimir Gliha, 1999, original scientific article

Abstract: Under-matched weld joints were adopted for producing a penstock of 47 mm wall thickness and 4200 mm diameter, to improve the weldability. The isothermal Robertson wide plate test on the under-matched weld joints, were the allowable stress level was 0.6 of the yield stress, proved that the longitudinal stresses caused the crack propagation alog the weld joint to deviate into tough base material where it was arrested. The arrest temperature was between -10 and -20°C. The behaviour of the crack propagation was the reason to omit the thermal stress relieving of the pipe section and on circumferential weld joints executed on this side. One can always take into consideration the role of axial residual stresses when assessing whether to use, or not, under-matched weld joints in severer loaded structures.
Keywords: strjeni zvar z nižjo mejo tečenja, zaostale napetosti, potek loma, lastnosti ujetja, lomna žilavost, under-matched weld joint, residual stresses, fracture path, arrest properties, fracture toughness
Published: 10.07.2015; Views: 885; Downloads: 24
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Strains and stresses of workers caused by exposure to noise
Andrej Polajnar, Nataša Vujica-Herzog, Borut Buchmeister, Simona Jevšnik, 2012, original scientific article

Abstract: 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.
Keywords: ergonomija, hrup na delovnem mestu, strain, stresses, ergonomic coefficient, noise, impulsive noise correction, tone correction
Published: 10.07.2015; Views: 587; Downloads: 18
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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: 1318; Downloads: 82
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Effect of residual stresses on the fatigue crack propagation in welded joints
Nenad Gubeljak, Jožef Predan, Reinhard Pippan, Maks Oblak, 2005, original scientific article

Abstract: The effect of residual stress on the fatigue crack growth was investigated forcyclic tension. Three-point bend specimens were used with through thicknessnotches at the center line of the welded joint. The experiments were performed for different load amplitudes and load ratios under conditions of small-scale yielding. The influence of the residual stresses on fatigue crack growth was estimated by experimentally observed fatigue crack growth rate and measurement of residual stresses at the surface of specimen. This paper describes an approach taken in two models to estimate the residual stress effect on fatigue crack propagation and to predict remaining service life of awelded structure.
Keywords: fracture mechnaics, fatigue crack, crack growth, residual stresses, fatigue crack growh rate, X-ray
Published: 01.06.2012; Views: 1395; Downloads: 70
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Effect of vibration on weld metal hardness and toughness
Bogdan Pučko, Vladimir Gliha, 2005, original scientific article

Abstract: Vibration of welded parts is usually applied to achieve effects similar to thermal stress relief. With vibration, it is not only residual stresses that are affected. Using two different welding processes, the influence of vibration on hardness and toughness of the weld was measured. For each weldingprocess, two series of Charpy specimens were made over the temperature range from -60 to +20°C. The only difference between the two series was in performing welding with or without vibration. Slight differences in weld metalhardness were observed. Toughness measurements show an increase in impacttoughness and a significant increase in fracture toughness in samples which were vibrated during welding.
Keywords: welding, welded joints, residual stresses, vibrational stress relief, hardness, toughness, steel
Published: 01.06.2012; Views: 1677; Downloads: 78
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