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Numerical analysis of the crack growth in a high loaded bolt connection
Marko Knez, Srečko Glodež, Janez Kramberger, 2007, original scientific article

Abstract: The paper deals with the research on the crack growth in a bolt connection of a lug for crane counter weight bars. Counter weight bars are structural elements subjected to very heavy loads and therefore need special attention. The main purpose of this research is to determine the number of load cycles required for a crack to propagate from initial to criticakl crack length, whenthe final failure can be expected to occur. All required material parameters and experimental results were determined in our previous research. The influence of the initial crack siye upon the remaining life of the lug is reserched numericallu by means of FE analysis and analytically by use of the corrected analystical model.
Keywords: fracture mechanics, cyclic loading, fatigue crack growth, service life prediction, numerical analysis, bolt connection
Published: 31.05.2012; Views: 1490; Downloads: 64
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Microcrack initiation and growth in heat-risistant 15Kh2MFA steel under cyclic loading
P. Yasniy, V.B. Hlado, V. Hutsaylyuk, Tomaž Vuherer, 2005, original scientific article

Abstract: This paper presents the results of investigation of a nuclear reactor pressurevessel steel 15Kh2MFA of two strength levels under cyclic loading. Themechanism of microcrack formation on the surface and in the bulk of 15Kh2MFA steel under cyclic deformation was investigated. Analysis of the specimen surfaces has shown that microcracks are caused by cyclic sliding in grains most favourably oriented with respect to the direction of the maximum shear stresses. Transmission electron microscope investigations show that microcracks in the material inside the grains are formed mainly along the band-type dislocation structure parallel to the dislocation subboundary. During cyclic deformation, the dislocation density on the subboundaries increases, in the local areas the dislocation density becomes limiting and it reaches the plasticity limit and causes microcrack formation. The interrelation of the average length of microcracks and their surface density with the energy density of inelastic deformation has been found.
Keywords: material testing, nuclear reactor, pressure vessel, cyclic loading, cyclic deformation, dislocation structure, fatigue crack growth, TEM, fracture mechanics
Published: 01.06.2012; Views: 1008; Downloads: 18
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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: 1180; Downloads: 57
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The influence of different parameters on surface pitting of contacting mechanical elements
Gorazd Fajdiga, Jože Flašker, Srečko Glodež, 2004, original scientific article

Abstract: The paper describes a general computational model for simulation of surface pitting of mechanical elements subjected to contact loading conditions. In the model it is assumed that the initial crack of length 0.015 mm is initiated at the contacting surfaces due to previously thermal, mechanical treatment of the material or running in process. The discretised model with the initial crack is then subjected to normal contact pressure, which takes into account the EHD lubrication conditions and tangential loading due to friction between contacting surfaces. The model accounts also for the influence of fluid trapped in the crack on crack prppagation. The virtual crack extension VCE method within FEM analysis is then used for 2 dimensional simulation of fatigue crack propagation from the initial crack up to the formation of the surface pit. The pit shapes and relationships between the stress intensity factor and crack length are determined for various combinations of contacting surface curvatures and loadings. The comparison of computational and available experimental results shows that the proposed model reliably simulates the surface fatigue crack growth under contact loading and can be used for computational predictions of surface pitting for various contacting mechanical elements.
Keywords: machine elements, gears, contact problems, pitting, fatigue crack growth, simulation, model
Published: 01.06.2012; Views: 1126; Downloads: 67
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Evaluation of the service life of gears in regrad to surface pitting
Srečko Glodež, Boris Aberšek, Jože Flašker, Zoran Ren, 2004, original scientific article

Abstract: A computational model for determining the service life of gear teeth flanks in regard to surface pitting is presented. The model considers the material fatigue process leading to pitting, i.e. the conditions required for the short fatigue crack propagation originating from the initial crack in a single material grain. In view of small crack lengths observed in surface pitting, the simulation takes into account the short crack growth theory. The stress field in the contact area and the required functional relationship between thestress intensity factor and the crack length are determined by the finite element method. An equivalent model of two contacting cylinders is used for numerical simulations of crack propagation in the contact area. On the basis of numerical results, and with consideration of some particular material parameters, the probable service life period of contacting surfaces is estimated for surface curvatures and loadings that are most commonly encountered in engineering practice.
Keywords: machine elements, gears, pitting, fatigue, short crack growth, numerical analysis, service life
Published: 01.06.2012; Views: 1428; Downloads: 14
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Closed form expression for fatigue life prediction at combined HCF/LCF loading
Damir Jelaska, Srečko Glodež, Srđan Podrug, 2003, original scientific article

Abstract: For combined HCF/LCF loading, whose stress history is simplified so that it consists of one LCF stress block with a number of cycles equal to the number of start-up in-service operations and one HCF stress block with all HCF cycles summed-up, we derived the closed form expression for estimating both the crack initiation life and the crack propagation life at combined HCF/LCF loading. As an example of use, Smith and Haigh diagrams were obtained for titanium alloy (Ti-6Al-4V) components, which enable to estimate the fatigue strength for the designed fatigue life, known load ratio and certain number of HCF cycles per one combined stress block.
Keywords: machine elements, fatigue, service life prediction, crack initiation, crack growth, stress history
Published: 01.06.2012; Views: 1367; Downloads: 21
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A computational model for determination of service life of gears
Srečko Glodež, Matjaž Šraml, Janez Kramberger, 2002, original scientific article

Abstract: A computational model for determination of service life of gears in regard to bending fatigue in a gear tooth root is presented. The fatique process leading to tooth breakage is divided into crack initiation and crack propagation period. The strain-life method in the framework of the FEM-methods has been used to determine the number of stress cycles Ni required for the fatique crack initiation, where it is assumed that the crack is initiated at the point of the largest stresses in a gear tooth root. The simple Paris equations is then used for the further simulation of the fatigue crack growth. The functional relationship between the stress intensity factor and crack length K=f(a), which is needed for determination ofthe required number of loading cycles Np for a crack propagation from the initial to the critical length, is obtained using displacement correlation method in the framework of the FEM-method. The total number of stress cycles N for the final failure to occur is then a sum of Ni and Np. The model is used for determination of service life of real spur gear made from through-hardened steel 42CrMo4, where required material parameters have been determined previously by the appropriate test specimens.
Keywords: machine elements, fatigue, fatigue crack growth, numerical modelling, gears, service life
Published: 01.06.2012; Views: 1406; Downloads: 74
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Determination of fatigue crack growth parameters in welded joint of HSLA steel
Ljubica Milović, Tomaž Vuherer, Zoran Radaković, Blagoj Petrovski, Miodrag D. Janković, Milorad Zrilić, Darko Daničić, 2011, published scientific conference contribution

Abstract: The structural integrity and operational safety of welded pressure vessels primarily depends on the behaviour of weldments. In spite of all efforts in material production and improvements in welding techniques, including strict codes, requirements and directives, the crack occurrence in welded structures cannot be completely excluded. This is why fracture mechanics analysis is inevitable in the structural integrity assessment of all welded structures. Examples of practical application of fracture mechanics parameters in cracked pressure vessel structural integrity are considered. This paper shows the determination of parameters of the fatigue crack for constituents of welded joints produced of high strength low alloyed steel Nionikral-70 (yield strength 700 MPa). Results have shown that the position of notch and crack initiation affect the values of the stress intensity range of fatigue threshold ?Kth and parameters in the Paris' equation.
Keywords: HSLA jekla, rast razpoke, HSLA steel, crack growth rate, fatigue threshold, Paris' law
Published: 10.07.2015; Views: 644; Downloads: 14
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Determination of calibration function for fatigue crack propagation by measurment[!] surface deformation
Bruno Glaser, Nenad Gubeljak, Jožef Predan, Patrik Gubeljak, Aleksandar Veg, 2013, original scientific article

Abstract: Components and structures exposed to elastic dynamic loading respond with elastic strains on the surface of the material. Mechanical response could be monitored by deformations on the surface. The measurements and monitoring of these parameters could be performed with electronic devices for on-line measurements, controlled by computerized systems. In the case of fatigue crack initiation and propagation the cyclic strain amplitude deviated from initial strain response (mean value and amplitude). Implementation of appropriate monitoring system supported by computerized programs for evaluation, analyses and activation represent important means to safe service component or construction. To evaluate flaw depth growth, the strain gauge measuring sensors could be used. These sensors measure surface deformation relaxation due to flaw depth growth. The monitoring of the material under cyclic loading could be performed with experimentally determined calibration curve, representing deformation on the surface and depth of the semi-elliptical crack growth on the surface or cross section of the material. The goal of this paper is describe electronic device and experimental procedure in order to determine calibration function.
Keywords: deformacije, elastičnost, rast razpoke, fatigue crack growth, surface deformation meaurement
Published: 10.07.2015; Views: 665; Downloads: 60
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