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1.
High-cycle fatigue behaviour of the aluminium alloy 5083-H111
Branko Nečemer, Franc Zupanič, Tomaž Vuherer, Srečko Glodež, 2023, izvirni znanstveni članek

Ključne besede: aluminium alloys, rolling direction, high-cycle fatigue, fracture analysis
Objavljeno v DKUM: 04.04.2024; Ogledov: 144; Prenosov: 13
.pdf Celotno besedilo (8,97 MB)
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2.
LCF behaviour of high strength aluminium alloys AA 6110A and AA 6086
Jernej Klemenc, Srečko Glodež, Matej Steinacher, Franc Zupanič, 2023, izvirni znanstveni članek

Opis: The proposed research presents the comprehensive investigation of the Low Cycle Fatigue (LCF) behaviour of two high-strength aluminium alloys of series AA 6xxx: the conventional alloy AA 6110A and the newly developed alloy AA 6086. Both alloys were characterised in the as-cast condition after homogenisation, extrusion, and T6 heat treatment. The quasi-static strength and hardness of the aluminium alloy AA 6086 were found to be significantly higher if compared to the AA 6110A alloys, while the ductility was a little bit smaller. The LCF tests showed that the AA 6086 alloy is more suitable for the high-cycle fatigue regime. On the other hand, the engineering advantage of the AA 6110A alloy is only for low-cycle fatigue applications if less than 100 loading cycles are expected in the service life of the analysed structure. The fatigue cracks formed predominantly on the α-AlMnSi intermetallic particles in both alloys, and, during LCF tests, exhibited small crack propagation. The area of the fatigue crack growth was much smaller than the area of the forced fracture. At smaller amplitude strains the fatigue striations were present at the fracture surface, while, at higher amplitude strains, they were not present. The obtained experimental results represent a good basis for engineering design applications of the analysed alloys AA 6086 and AA 6110A.
Ključne besede: aluminijeve zlitine, malociklično utrujanje, eksperimentalno testiranje, fraktografija, aluminium alloys, low cycle fatigue, experimental testing, fractography
Objavljeno v DKUM: 29.03.2024; Ogledov: 140; Prenosov: 12
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3.
Razvoj modela za spremljanje degradacije površine materiala med dinamičnim obremenjevanjem : doctoral disertation
Marijana Milković, 2023, doktorska disertacija

Opis: The study focuses on the behavior of the AA7075-T6 material, widely used in the aerospace industry, under dynamic loadings. The material undergoes processing, including cold rolling and stretching, resulting in residual stress compressive stresses on its surface. The research centers on monitoring changes in the surface condition during dynamic loaidngs using Fiber Bragg Grating (FBG) sensors and numerical simulations. The dissertation includes experimental testing of AA 7075-T6 material samples, numerical simulations of optical fiber responses to tensile loads, and an investigation of surface condition changes using techniques such as focused ion beam engraving and scanning electron microscope observation. The study has shown that the surface condition of the material changes even under low dynamic loads, including variations in surface roughness, residual stresses, and FBG response. Despite low load levels, changes in FBG sensor spectra are observable. The dissertation concludes that the surface condition of the material changes during dynamic loadings, detectable through FBG sensors. It underscores the effectiveness of FBG sensors in monitoring stress levels throughout the material’s service life, particularly on the side lobes of the spectral response. In summary, the research on the dynamic behavior of the AA7075-T6 alloy offers valuable insight into surface condition changes that can impact the integrity and durability of materials in the aerospace industry.
Ključne besede: fatigue, high cycle load, Fiber Bragg grating
Objavljeno v DKUM: 05.01.2024; Ogledov: 398; Prenosov: 39
.pdf Celotno besedilo (10,61 MB)

4.
Effect of residual stresses on fatigue strength on the smooth and splined parts of spring torsion bars
Vinko Močilnik, Jožef Predan, Nenad Gubeljak, 2023, izvirni znanstveni članek

Opis: The article discusses the effect of residual stresses on the fatigue strength of torsion bars by using the Dang Van fatigue criterion, at the stress concentration at the root of the tooth and at the smooth part of the torsion bar. Residual compressive stresses were induced on the surface during the technological processes by cold surface rolling and torsional pre-strain (pre-setting) to the plastic range, to increase the elastic linear range and to reduce the stress state during torsional loading. Normally, the stress reduction in the torsion bar at the mounting point is provided by the increased diameter of the splined part, compared to the smooth part of the torsion bar. In the case of a small difference between the diameter of the splined and the smooth parts of the torsion bar, a fatigue crack can be initiated in the notch, which causes the torsion bar to break during operation after a few hundred loading cycles. FEM stress analysis of a torsion bar was performed in the article. The actual residual stresses were measured by the non-destructive X-ray method at the place of stress concentration on the smooth and splined parts with a notch of the torsion bar, and Dang Van’s failure criterion was used to determine the fatigue behavior during torsional loading. Therefore, in the paper, the three methods were combined to determine the optimum lifetime of a torsion bar exposed to the required cyclic torque. The results of the analysis showed that the residual compressive stresses are useful up to a certain limit where the retarded fatigue crack initiation occurred, but a further increase of compressive stress caused an increase of the maximum shear stresses, which, in turn, caused the initiation of fatigue and failure at the splined part of the torsion bar before achieving the required number of cycles.
Ključne besede: Dang Van fatigue criterion, torsion bars, pre-setting, high-cycle fatigue, residual stress
Objavljeno v DKUM: 30.11.2023; Ogledov: 392; Prenosov: 23
.pdf Celotno besedilo (7,29 MB)
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5.
Damage and failure modeling of lotus-type porous material subjected to low-cycle fatigue
Janez Kramberger, Klemen Sterkuš, Srečko Glodež, 2016, izvirni znanstveni članek

Opis: The investigation of low-cycle fatigue behaviour of lotus-type porous material is presented in this paper. Porous materials exhibit some unique features which are useful for a number of various applications. This paper evaluates a numerical approach for determining of damage initiation and evolution of lotus-type porous material with computational simulations, where the considered computational models have different pore topology patterns. The low-cycle fatigue analysis was performed by using a damage evolution law. The damage state was calculated and updated based on the inelastic hysteresis energy for stabilized cycle. Degradation of the elastic stiffness was modelled using scalar damage variable. In order to examine crack propagation path finite elements with severe damage were deleted and removed from the mesh during simulation. The direct cyclic analysis capability in Abaqus/Standard was used for low-cycle fatigue analysis to obtain the stabilized response of a model subjected to the periodic loading. The computational results show a qualitative understanding of pores topology influence on low-cycle fatigue under transversal loading conditions in relation to pore orientation.
Ključne besede: porous materials, low-cycle fatigue, damage, finite element analysis
Objavljeno v DKUM: 02.08.2017; Ogledov: 1227; Prenosov: 391
.pdf Celotno besedilo (2,32 MB)
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6.
Computational simulation of biaxial fatigue behaviour of lotus-type porous material
Janez Kramberger, Marko Šori, Matjaž Šraml, Srečko Glodež, 2016, izvirni znanstveni članek

Opis: A computational simulation of low-cycle fatigue behaviour of lotus-type porous material, subjected to biaxial in-phase loading cycles is presented in this paper. Fatigue properties of porous materials are less frequently published in the literature. This paper evaluates computational analyses, where different pore distribution and biaxial loading conditions in relation to the pore orientations is considered in each simulation. The fatigue analysis is performed by using a damage initiation and evolution law based on the inelastic strain energy. The computational results are subjected to the appropriate statistical analysis, because of different pore topology a different fatigue lives are obtained on the same loading level. Results of computational simulations show also a qualitative understanding of porosity influence on low-cycle fatigue failures of lotus-type porous material under biaxial loading conditions.
Ključne besede: Lotus-type porous material, low-cycle fatigue, damage, finite element analysis
Objavljeno v DKUM: 02.08.2017; Ogledov: 1419; Prenosov: 405
.pdf Celotno besedilo (1,08 MB)
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7.
Experimental determination of fatigue parameters of high chromium steel under different loading and temperature conditions
Matej Drobne, Nenad Gubeljak, Srečko Glodež, 2014, izvirni znanstveni članek

Opis: Fatigue investigation of high chromium steel (HCS) at different loading ratios (R = 0, R = -1) and different temperatures (20 °C, 600 °C) is presented in this paper. Before fatigue testing, monotonic mechanical properties (ultimate compressive and ultimate tensile strength) are determined at different temperatures, using standardized testing procedures according to DIN 50125 standard. Moreover Charpy impact tests at different temperatures were done with specimens that comply with the standard ISO 14556. Fatigue testing is performed on a servo - hydraulic testing machine with consideration of different loading conditions as described above. On the basis of the experimental results the S - N curves are constructed from which typical fatigue parameters (the fatigue strength coefficient 0'f and the fatigue strength exponent b) are determined. After fatigue testing a comprehensive investigation of fracture surfaces is performed using the Scanning Electron Microscope (SEM). Experimental results presented in this paper will serve as a basis for further investigations related to fatigue behaviour of real working rolls in hot strip mills made of HCS.
Ključne besede: experiments, high chromium steel, high cycle fatigue, fracture mechanics
Objavljeno v DKUM: 12.07.2017; Ogledov: 1128; Prenosov: 133
.pdf Celotno besedilo (2,88 MB)
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8.
An integrity analysis of washing machine holders
Nenad Gubeljak, Matej Mejač, Jožef Predan, 2007, izvirni znanstveni članek

Opis: The paper deals with structure integrity analysis of the holder for the carrying cross of a washing machine drum. Premature fracture of the holder occurred between mechanical sustainable tests of washing machine in the factory. In order to prevent fracture, the task was to determine the reasons for premature fracture of the holder and to estimate the suitability of the new design of the holder cross. Input data for structure integriry analysis were obtained by material by mechanical testing of used materials. Stress and strain analysis of holder limit load was performed by finite element modeling of holder. Dynamic tests of holders with two different thicknesses were done on a servo-hydraulic machine in order to find dynamical strength and endurance of holder. Fracture behaviour of holders is defined as initiation and propagation of crack. The obtained behaviour confirmed that the new design of holders reduces stress concentration in the critical region. Consequently, the new holder subjected to the same dynamic load can endure a higher number of cycles until breakage. The total number of cycles overcomes industrial testing requirements.
Ključne besede: lomna mehanika, visokociklično utrujanje, preizkušanje lomne žilavosti, nosilci kadi pralnega stroja, mejna obremenitev, ocena celovitosti konstrukcije, fracture mechanics, high cycle fatigue, fracture toughness testing, washing machine holders, washing machine drums, structure integrity assessment, limit load
Objavljeno v DKUM: 10.07.2015; Ogledov: 1798; Prenosov: 109
.pdf Celotno besedilo (517,04 KB)
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