1. Generalised computational analysis of contact fatigue initiationMatjaž Šraml, Zoran Ren, Jože Flašker, Iztok Potrč, Miran Ulbin, 2002, published scientific conference contribution abstract Keywords: machine elements, fracture mechanics, contact problems, fatigue, computational analysis
Published in DKUM: 01.06.2012; Views: 1642; Downloads: 24
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2. Numerical procedure for predicting the rolling contact fatigue crack initiationMatjaž Šraml, Jože Flašker, Iztok Potrč, 2003, original scientific article Abstract: A computational numerical model for contact fatigue damage analysis of mechanical elements is presented in this paper. The computational approach is based on continuum mechanics, where a homogenous and elastic material model isassumed in the framework of the finite element method analysis. Cyclic contact loading conditions are simulated with moving Hertzian contact pressure. The time-depending loading cycles are defined for each observed material point on and under the contact area. Furthermore, the influence of friction upon rolling-sliding contact loading cycles is analysed in detail, using Coulombćs friction law. The model for prediction of the number of loading cycles, required for initial fatigue damages to appear, is based on Coffin-Manson relations between deformations and loading cycles, and includes characteristic material fatigue parameters. As a general example, the model isused to analyse a fundamental contact problem of a cylinder and flat surface, which is usually a substitutional model for analysing real mechanicalproblems. However, the results concerning the identification of critical material points and the number of loading cycles, required for initial fatigue damages to appear at those points, are the main purpose of thepresented study.
Keywords: machine elements, gears, contact problems, contact fatigue, crack initiation, numerical modelling
Published in DKUM: 01.06.2012; Views: 1935; Downloads: 81
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3. Symmetry preserving algorithm for large displacement frictionless contact by the pre-discretization penalty methodDušan Gabriel, Jiři Plešek, Miran Ulbin, 2004, original scientific article Abstract: A three-dimensional contact algorithm based on the pre-discretization penalty method is presented. Using the pre-discretization formulation gives rise to contact searching performed at the surface Gaussian integration points. It is shown that the proposed method is consistent with the continuum formulation ofthe problem and allows an easy incorporation of higher-order elements with midside nodes to the analysis. Moreover, a symmetric treatment of mutually contacting surfaces is preserved even under large displacement increments. Theproposed algorithm utilizes the BFGS method modified for constrained non-linear systems. The effectiveness of quadratic isoparametric elements in contact analysis is tested in terms of numerical examples verified by analytical solutions and experimental measurements. The symmetry of the algorithm is clearly manifested in the problem of impact of two elastic cylinders.
Keywords: mechanics, numerical methods, contacting surfaces, contact problems, 3D contact algorithm, discretization, higher order elements, finite element method, Gauss point search, pre-discretization penalty method
Published in DKUM: 01.06.2012; Views: 2552; Downloads: 88
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4. The influence of different parameters on surface pitting of contacting mechanical elementsGorazd 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 in DKUM: 01.06.2012; Views: 2182; Downloads: 111
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