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1.
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: 676; Downloads: 84
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2.
Fatigue crack growth and fracture mechanics analysis of a working roll surface layer material
Matej Drobne, Tomaž Vuherer, Ivan Samardžić, Srečko Glodež, 2014, original scientific article

Abstract: Fatigue crack growth and fracture mechanics analysis of a working roll surface layer material is presented in this paper. The research is done on a hot strip mill working roll where High Chromium Steel is used for roll’s shell material. To obtain corresponding parameters, a rectangular single edge notched bend specimens – SENB, according to standard BS 7448, were used. The fatigue crack growth analysis was done on a resonant testing machine with use of special crack gauges, while for fracture mechanics parameters the electro–mechanical testing machine was used.
Keywords: fracture mechanics, fatigue crack growth, metal forming, rolling process, high chromium steel
Published: 03.07.2017; Views: 526; Downloads: 83
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3.
Numerical modelling of crack growth in a gear tooth root
Srđan Podrug, Srečko Glodež, Damir Jelaska, 2011, original scientific article

Abstract: A computational model for determination of crack growth in a gear tooth root is presented. Two loading conditions are taken into account: (i) normal pulsating force acting at the highest point of the single tooth contact and (ii) the moving load along the tooth flank. In numerical analysis it is assumed that the crack is initiated at the point of the largest stresses in a gear tooth root. The simple Paris equation is then used for a 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 determining the required number of loading cycles N for a crack propagation from the initial to the critical length, is obtained using a displacement correlation method in the framework of the FEM-method considering the effect of crack closure. The model is used for determining fatigue crack growth in a real gear made from case carburised and ground steel 14CiNiMo13-4, where the required material parameters were determined previously by appropriate test specimens. The results of the numerical analysis show that the prediction of crack propagation live and crack path in a gear tooth root are significantly different for both loading conditions considered.
Keywords: zobniki, utrujanje, širjenje razpoke, numerično modeliranje, gears, fatigue, crack growth, numerical modelling
Published: 10.07.2015; Views: 668; Downloads: 67
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4.
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: 974; Downloads: 75
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5.
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: 1097; Downloads: 23
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6.
7.
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: 1649; Downloads: 99
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8.
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: 1649; Downloads: 28
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9.
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: 1715; Downloads: 19
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10.
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: 1421; Downloads: 92
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