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Opis: Numerical simulation of fatigue crack growth in welded joints is not well represented in the literature, especially from the point of view of material heterogeneity in a welded joint. Thus, several case studies are presented here, including some focusing on fracture, presented by two case studies of mismatched high-strength low-alloyed (HSLA) steel welded joints, with cracks in the heat affected zone (HAZ) or in weld metal (WM). For fatigue crack growth, the extended finite element method FEM (XFEM) was used, built in ABAQUS and ANSYS R19.2, as presented by four case studies, two of them without modelling different properties of the welded joint (WJ). In the first one, fatigue crack growth (FCG) in integral (welded) wing spar was simulated by XFEM to show that its path is partly along welded joints and provides a significantly longer fatigue life than riveted spars of the same geometry. In the second one, an integral skin-stringer panel, produced by means of laser beam welding (LBW), was analysed by XFEM in its usual form with stringers and additional welded clips. It was shown that the effect of the welded joint is not significant. In the remaining two papers, different zones in welded joints (base metal—BM, WM, and HAZ) were represented by different coefficients of the Paris law to simulate different resistances to FCG in the two cases; one welded joint was made of high-strength low-alloyed steel (P460NL1) and the other one of armour steel (Protac 500). Since neither ABAQUS nor ANSYS provide an option for defining different fatigue properties in different zones of the WJ, an innovative procedure was introduced and applied to simulate fatigue crack growth through different zones of the WJ and evaluate fatigue life more precisely than if the WJ is treated as a homogeneous material.
Ključne besede: fatigue crack growth, extended finite element method, welded joints, fatigue life, highstrength low-alloyed steel
Objavljeno v DKUM: 25.11.2024; Ogledov: 0; Prenosov: 7
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Opis: Standard procedure for bearing life calculation, as described in standard ISO281:2008, was developed for standard, rather small axial or thrust rolling bearings. Since the geometry and manufacturing procedures of large rolling slewing bearings are considerably different from those of standard rolling bearings, different calculation procedures have to be used. The paper describes a computational procedure, where the geometry of the bearing is described with vectors, which enables modelling of irregular shapes of the bearing rings. These can be a result of the manufacturing procedure or of the deformations caused by the operating conditions. The calculation procedure consists of calculation of the maximum contact force on the rolling element, which is done by the in-house developed program, and detailed finite element analysis of the contact between the ball and the raceway. The finite element analysis also takes into account depth-dependent material parameters of a raceway. Different calculation theories are then used for the calculation of fatigue life, and a comparison of the results is made at the end.
Ključne besede: fatigue life, bearings
Objavljeno v DKUM: 07.06.2012; Ogledov: 1946; Prenosov: 120
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Opis: 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.
Ključne besede: machine elements, fatigue, service life prediction, crack initiation, crack growth, stress history
Objavljeno v DKUM: 01.06.2012; Ogledov: 2594; Prenosov: 53
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Opis: Contact fatigue is a phenomenon of important practical significance for engineering applications involving localized contacts, such as gears, rail wheel system and rolling bearings. The service lifetime of such components is related to damage, which results from the contact fatigue. The process in the material structure that causes this kind of failure is quite complicated. The aim of the present paper is to describe a contact fatigue initiation criterion, based on the critical plane approach for the general contact problem. On the basis of contact stress analysis with modified Hertzian boundary conditions, the loading cycle of characteristic material points in the contact area is determined. The Dang Van damage initiation criterion is based on the critical plane approach, which combines the largest allowable shearing and hydrostatic stresses (tensile and compressive), with an assumed elastic shakedown behaviour and it is used in this work. The material point of initial fatigue damage is then determined at the transition of the loading cycle stresses over the critical plane. The model assumed a homogeneous and elastic material model, without any imperfections or residual stresses, and elastic shakedown is considered. A proper determination of loading cycles and their characteristic values is of significance for contact fatigue initiation analysis. Finally, determination of the most critical material point on or under the contact surface and related number of loading cycles required for fatigue damage initiation is calculated with the strain-life (▫$epsilon$▫-N) method.
Ključne besede: machine elements, contact fatigue, crack initiation, strain life method, critical plane approach, numerical modeling
Objavljeno v DKUM: 01.06.2012; Ogledov: 2046; Prenosov: 117
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Opis: Mechanical elements subjected to cyclic loading have to be designed against fatigue. The main goal of the presented analysis was to determine the the bending fatigue life prediction of thin rim spur gears. The service life is divided into the initiation phase of the damage accumulation and the crack growth, resprcitively. The analysis has been performed usig FEM and BEM. The continuum mechanics approach is used for the prediction of the fatigue life initiation phase, where the basic fatigue material parameters are taken into account. The evaluation of the structure remaining life with initial crack the linear-elastic fracture mechanics LEFM principles are applied.
Ključne besede: machine elements, lineaar elastic fracture mechanics, fatigue, bending, initial crack, service life
Objavljeno v DKUM: 01.06.2012; Ogledov: 2558; Prenosov: 110
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