1. Fatigue crack initiation and propagation in lotus-type porous materialSrečko Glodež, Sašo Dervarič, Janez Kramberger, Matjaž Šraml, 2016, izvirni znanstveni članek Opis: The investigation of fatigue strength of lotus-type structure with nodular cast iron as a base material using computational model is analysed in present study. The irregular pores distribution in transversal and longitudinal direction, regarding the external loading, is considered in the computational models. The complete fatigue process of analyzed porous structure is then divided into the crack initiation (Ni) and crack propagation (Np) period where the total fatigue life (N) is defined as: N = Ni + Np. The crack initiation period is determined using strain life approach where elastic-plastic numerical analysis is performed to obtain the total strain amplitude in the critical stress fields around the pores. The simplified universal slope method is then used to determine the number of stress cycles, Ni, required for formation of initial cracks. The number of stress cycles, Np, required for crack propagation from initial to the critical crack length is also numerically determined using finite element (FE) models, in the frame of Abaqus computation FEM code. The maximum tensile stress (MTS) criterion is considered when analyzing the crack path inside the porous structure. The performed computational analyses show that stress concentrations around individual pores are higher when external loading is acting in transversal direction in respect to the pore distribution. Therefore, further computational analyses regarding crack initiation and crack propagation period have been done only for pores distribution in transversal direction. Ključne besede: lotus-type porous structures, fatigue crack initiation, fatigue crack propagation, numerical analysis Objavljeno v DKUM: 02.08.2017; Ogledov: 972; Prenosov: 375 Celotno besedilo (4,75 MB) Gradivo ima več datotek! Več... |
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3. Measurement of strain caused by residual stresses in a welded joint using neutron diffractionNenad Gubeljak, Jelena Vojvodič-Tuma, Hans-Georg Preismeyer, 1999, izvirni znanstveni članek Opis: 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. Ključne besede: zaostale napetosti, zvarni spoj, neutronski lom žarkov, utrujenostno širjenje razpoke, neutron diffraction method, residual stresses, fatigue crack propagation, weld joint Objavljeno v DKUM: 10.07.2015; Ogledov: 949; Prenosov: 28 Povezava na celotno besedilo |
4. Behaviour of short cracks emanating from tiny drilled holesVladimir Gliha, P. O. Maruščak, Tomaž Vuherer, 2013, izvirni znanstveni članek Opis: Specimens with martensitic microstructure were defected by tiny drilled holes with the existing local residual stresses induced by drilling and without them. The objective of this research was to determine the cyclic stress level for the crack initiation and fatigue limit of the defected and smooth specimens' dependence upon the residual-stress field. Compressive residual stresses retarded the crack initiation. Immediately after the crack initiation, residual stresses decelerated the short-crack propagation, but later, when the residual-stress sign was changed, they accelerated it. Non-propagating short-crack size and fatigue limit also depend on the residual-stress field. Ključne besede: small defect, drilled hole, crack initiation, crack propagation, short crack, long crack, anomalous fast-crack propagation Objavljeno v DKUM: 10.07.2015; Ogledov: 994; Prenosov: 104 Celotno besedilo (1,42 MB) Gradivo ima več datotek! Več... |
5. Fatigue behaviour of 42CrMo4 steel under contact loadingPéter Göncz, Rok Potočnik, Srečko Glodež, 2010, izvirni znanstveni članek Opis: The presented paper describes the experimental determination of fatigue crack growth parameters for high strength low-alloy steel 42CrMo4. The experiments were performed according to the ASTM E647 standard and the parameters of the Paris equation (C and m) were determined. Test specimens were subjected to impulsive cyclic tensile loading on a testing machine. During that the fatigue crack propagation was monitored as a function of elapsed fatigue cycles. Taking these experimental results into account the fatigue crack growth rates at different stress-intensity factor ranges was determined. To consider the variable material properties of the slewing bearing ring trough depth, specimens of different hardnesses were tested. Beside the experimental result a 2D contact fatigue crack propagation model is also presented. This model can be used for the simulation of surface initiated contact fatigue crack propagation on the roller slewing bearing's raceway. As a computational example the results of a finite element method contact fatigue crack propagation simulation are presented. Ključne besede: crack propagation, slewing bearings, numerical modelling, experiments Objavljeno v DKUM: 07.06.2012; Ogledov: 1740; Prenosov: 84 Povezava na celotno besedilo |
6. Evaluation of stress intensity factors using finite elementsBoštjan 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 v DKUM: 01.06.2012; Ogledov: 2144; Prenosov: 38 Povezava na celotno besedilo |
7. Numerical modelling of micro-pitting of gear teeth flanksGorazd Fajdiga, Jože Flašker, Srečko Glodež, Trevor K. Hellen, 2003, izvirni znanstveni članek Opis: A two-dimensional computational model for simulation of contact fatigue of gear teeth flanks is presented. In the model, it is assumed that the initial crack of length 0.015 mm is initiated at the surface due to previous mechanical or heat treatment of the material as well as a consequence of the running in process. The discretized model with the initial crack is then subjected to normal contact pressure, which takes into account the elasto-hydro-dynamic (EHD) lubrication conditions, and tangential loading due to friction between contacting surfaces. The model also considers the moving contact of gear flanks, fluid trapped in the crack and residual stresses due to heat treatment of the material on crack propagation. The virtual crack extension (VCE) method, implemented in the finite element method, is then usedfor simulating the fatigue crack growth from the initial crack up to the formation of the surface pit. The computational results show that the initial surface crack of length 15 m and the considered boundary conditions lead to the appearance of very small surface pits, which can be termed as micro-pitting on gear teeth flanks. The numerical results correspond well withavailable experimental data. Ključne besede: machine elements, gearing, fracture mechanics, numerical analysis, micro pitting, pitting simulation, matematical model, fatigue, contact mechanics, crack propagation Objavljeno v DKUM: 01.06.2012; Ogledov: 2170; Prenosov: 0 |
8. Computational model for the analysis of bending fatigue in gearsJanez Kramberger, Matjaž Šraml, Srečko Glodež, Jože Flašker, Iztok Potrč, 2004, izvirni znanstveni članek Opis: A computational model for the determination of service life of gears with regard to bending fatigue in a gear tooth root is presented. The fatigue process leading to tooth breakage is divided into crack initiation (Ni) and crack propagation (Np) periods, where the complete service life is defined as N = Ni + Np. The strain-life method in the framework of the FEM method has been used to determine the number of stress cycles Ni required for fatigue crack initiation. Gear tooth crack propagation was simulated using a FEM method based computer program which uses principles of linear elastic fracture mechanics. The Paris equation is then used for the further simulation of the fatigue crack growth. The presented model is used to determine the service life of a real spur gear made from through-hardened steel 42CrMo4. Ključne besede: machine elements, gears, bending fatigue, service life, fatigue crack initiation, fatigue crack propagation, computational simulations, numerical modelling, fracture mechanics Objavljeno v DKUM: 01.06.2012; Ogledov: 2824; Prenosov: 91 Povezava na celotno besedilo |
9. Investigation of crack propagation scatter in a gear tooth's rootStanislav Pehan, Janez Kramberger, Jože Flašker, Boštjan Zafošnik, 2008, izvirni znanstveni članek Opis: This paper describes the problem of determining crack initiation location and its influence on crack propagation in a gear tooth's root. Three different load positions on the gear tooth's flank were considered for this investigation of crack initiation and propagation. A special test device was used for the single tooth test. It can be concluded from the measurements thata crack can be initiated at very different locations in a tooth's root and then propagate along its own paths. A numerical investigation into a crack initiation's position and its influences on its propagation were carried out within the framework of linear fracture mechanics. The influence of a tooth's load position, the geometry of the tooth's root, and the influence of nonparallel load distribution on the tooth's flank were considered when investigating the crack initiation's position. Results show that linear fracture mechanics can be used for determining crack propagation, if better initial conditions for crack initiation are considered. Ključne besede: fracture mechanics, crack initiation, experimental crack propagation, numerical crack propagation, crack location, gearbox, tooth root, load distribution, linear elastic fracture mechanics Objavljeno v DKUM: 01.06.2012; Ogledov: 1447; Prenosov: 97 Povezava na celotno besedilo |
10. Influence of different load models on gear crack path shapes and fatigue livesSrđan Podrug, Damir Jelaska, Srečko Glodež, 2008, izvirni znanstveni članek Opis: A computational model for determination of the service life of gears with regard to bending fatigue at gear tooth root is presented. In conventional fatigue models of the gear tooth root, it is usual to approximate actual gear load with a pulsating force acting at the highest point of the single tooth contact. However, in actual gear operation, the magnitude as well as the position of the force changes as the gear rotates. A study to determine the effect of moving gear tooth load on the gear service life is performed. The fatigue process leading to tooth breakage is divided into crack-initiation and crack-propagation period. The critical plane damage model has been used to determine the number of stress cycles required for the fatigue crack initiation. The finite-element method and linear elastic fracture mechanics theories are then used for the further simulation of the fatigue crack growth. Ključne besede: crack closure, crack initiation, crack propagation, gear tooth root, moving load Objavljeno v DKUM: 31.05.2012; Ogledov: 1240; Prenosov: 87 Povezava na celotno besedilo |