The Experts below are selected from a list of 147 Experts worldwide ranked by ideXlab platform

Luboš Náhlík - One of the best experts on this subject based on the ideXlab platform.

  • effect of the free surface on the fatigue crack front curvature at high stress asymmetry
    International Journal of Fatigue, 2019
    Co-Authors: Tomas Oplt, Zdeněk Chlup, Pavel Hutar, Luboš Náhlík, Pavel Pokorný, Filippo Berto
    Abstract:

    Abstract The purpose of this paper is to investigate the effect of the vertex Singularity on the fatigue crack front behaviour. Single edge notch bend specimens of steel EA4T and aluminium alloy 7075 of various thicknesses are subjected to the cyclic loading and the angles of the fatigue crack front curvature was measured. The experimental procedure is simulated using finite element analysis. Two methodologies used for the fatigue crack front shape estimation are compared. One is using stress Singularity Exponent as a controlling parameter and the second one is using stress intensity factor. Both methodologies provide comparable results of crack front formation process and they are in very good agreement with experimental results.

  • estimation of critical applied stress for crack initiation from a sharp v notch
    Theoretical and Applied Fracture Mechanics, 2018
    Co-Authors: Luboš Náhlík, Kateřina Stegnerova, Pavel Hutař
    Abstract:

    Abstract The aim of this paper is to estimate the critical applied stress value for a crack initiated from a sharp V-notch tip. The classical approach of linear elastic fracture mechanics (LELM) was generalized because the stress Singularity Exponent differs from 0.5 in the studied case. The value of the stress Singularity Exponent depends on the V-notch opening angle. The finite element method was used to determine the stress distribution near the sharp V-notch tip and for estimating the generalized stress intensity factor depending on the V-notch opening angle. The critical value of the generalized stress intensity factor was obtained using stability criteria based on the tangential stress component averaged over a critical distance from the V-notch tip and the generalized strain energy density factor. These criteria were applied in the case of corner stress Singularity, as well. The calculated values of the critical applied stresses were compared with the experimental data from the literature, and the applicability of the LEFM concept is discussed.

  • critical applied stresses for a crack initiation from a sharp v notch
    Frattura ed Integrità Strutturale, 2014
    Co-Authors: Luboš Náhlík, Pavel Huta, Kateřina Stegnerova
    Abstract:

    The aim of the paper is to estimate a value of the critical applied stress for a crack initiation from a sharp V-notch tip. The classical approach of the linear elastic fracture mechanics (LELM) was generalized, because the stress Singularity Exponent differs from 0.5 in the studied case. The value of the stress Singularity Exponent depends on the V-notch opening angle. The finite element method was used for a determination of stress distribution in the vicinity of the sharp V-notch tip and for the estimation of the generalized stress intensity factor depending on the V-notch opening angle. Critical value of the generalized stress intensity factor was obtained using stability criteria based on the opening stress component averaged over a critical distance d from the V-notch tip and generalized strain energy density factor. Calculated values of the critical applied stresses were compared with experimental data from the literature and applicability of the LEFM concept is discussed.

  • influence of the v notch opening angle on critical applied force values for the crack initiation from the sharp v notch
    Key Engineering Materials, 2014
    Co-Authors: Kateřina Stegnerova, Luboš Náhlík, Pavel Hutař
    Abstract:

    The aim of this paper is to estimate a value of the critical applied force for a crack initiation from the sharp V-notch tip. The classical approach of the linear elastic fracture mechanics (LELM) was generalized, because the stress Singularity Exponent differs from 0.5 in studied case. The value of the stress Singularity Exponent depends on the V-notch opening angle. The finite element method was used for a determination of stress distribution in the vicinity of the sharp V-notch tip and for the estimation of the generalized stress intensity factor depending on the V-notch opening angle. Critical value of generalized stress intensity factor was obtained by using stability criterion based on the tangential stress component averaged over a critical distance d from the V-notch tip. Calculated values of the critical applied force were compared with experimental data taken from the literature.

  • critical value for crack propagation from sharp v notch
    Key Engineering Materials, 2013
    Co-Authors: Luboš Náhlík, Pavel Hutař, Kateřina Stegnerova, Zdeněk Majer
    Abstract:

    The contribution is focused on estimation of a critical value of generalized stress intensity factor for crack propagation from sharp V-notches. Stress distribution around the tip of the V-notch is described on the base of generalized linear elastic fracture mechanics, because V-notch is a singular stress concentrator with stress Singularity Exponent different from 0.5 (depending on V-notch opening angle). Then also stability criteria based on strain energy density factor and average critical stress are generalized for the stress Singularity different from 0.5. Using FE analysis the critical stresses for crack initiation was estimated and compared with experimental data from the literature.

Pavel Hutař - One of the best experts on this subject based on the ideXlab platform.

  • estimation of critical applied stress for crack initiation from a sharp v notch
    Theoretical and Applied Fracture Mechanics, 2018
    Co-Authors: Luboš Náhlík, Kateřina Stegnerova, Pavel Hutař
    Abstract:

    Abstract The aim of this paper is to estimate the critical applied stress value for a crack initiated from a sharp V-notch tip. The classical approach of linear elastic fracture mechanics (LELM) was generalized because the stress Singularity Exponent differs from 0.5 in the studied case. The value of the stress Singularity Exponent depends on the V-notch opening angle. The finite element method was used to determine the stress distribution near the sharp V-notch tip and for estimating the generalized stress intensity factor depending on the V-notch opening angle. The critical value of the generalized stress intensity factor was obtained using stability criteria based on the tangential stress component averaged over a critical distance from the V-notch tip and the generalized strain energy density factor. These criteria were applied in the case of corner stress Singularity, as well. The calculated values of the critical applied stresses were compared with the experimental data from the literature, and the applicability of the LEFM concept is discussed.

  • influence of the v notch opening angle on critical applied force values for the crack initiation from the sharp v notch
    Key Engineering Materials, 2014
    Co-Authors: Kateřina Stegnerova, Luboš Náhlík, Pavel Hutař
    Abstract:

    The aim of this paper is to estimate a value of the critical applied force for a crack initiation from the sharp V-notch tip. The classical approach of the linear elastic fracture mechanics (LELM) was generalized, because the stress Singularity Exponent differs from 0.5 in studied case. The value of the stress Singularity Exponent depends on the V-notch opening angle. The finite element method was used for a determination of stress distribution in the vicinity of the sharp V-notch tip and for the estimation of the generalized stress intensity factor depending on the V-notch opening angle. Critical value of generalized stress intensity factor was obtained by using stability criterion based on the tangential stress component averaged over a critical distance d from the V-notch tip. Calculated values of the critical applied force were compared with experimental data taken from the literature.

  • critical value for crack propagation from sharp v notch
    Key Engineering Materials, 2013
    Co-Authors: Luboš Náhlík, Pavel Hutař, Kateřina Stegnerova, Zdeněk Majer
    Abstract:

    The contribution is focused on estimation of a critical value of generalized stress intensity factor for crack propagation from sharp V-notches. Stress distribution around the tip of the V-notch is described on the base of generalized linear elastic fracture mechanics, because V-notch is a singular stress concentrator with stress Singularity Exponent different from 0.5 (depending on V-notch opening angle). Then also stability criteria based on strain energy density factor and average critical stress are generalized for the stress Singularity different from 0.5. Using FE analysis the critical stresses for crack initiation was estimated and compared with experimental data from the literature.

  • fatigue crack shape prediction based on the stress Singularity Exponent
    Key Engineering Materials, 2011
    Co-Authors: Pavel Hutař, Martin Sevcik, Luboš Náhlík, Zdeněk Knésl
    Abstract:

    In many industrial applications it is necessary to predict fatigue lifetime of the structures where the stress field near the crack front have a three-dimensional nature. Due to the existence of vertex Singularity in the point where the crack front touches free surface, crack propagation in 3D structures cannot be reduced to a series of plane strain or plane stress problems along the crack front. The paper describes the influence of the vertex Singularity on crack shape for three-dimensional structure. The iterative process for estimation of a real crack front based on a stress Singularity Exponent is presented. In each node defining the crack front the stress Singularity Exponent has been estimated and complete crack front shape corresponding to the constant stress Singularity Exponent was found. The methodology presented can help to estimate crack front shape in a linear elastic fracture mechanics framework and estimate fracture parameters of fatigue cracks more accurately.

  • The effect of a free surface on fatigue crack behaviour
    International Journal of Fatigue, 2010
    Co-Authors: Pavel Hutař, Luboš Náhlík, Zdeněk Knésl
    Abstract:

    Abstract The effect of a free surface on fatigue crack behaviour is discussed in the paper and generalized stress intensity factor methodology is used for a reliable estimation of the fatigue crack propagation rate in the area close to a free surface, where the effect of vertex Singularity is important. It is shown that a decrease in the stress Singularity Exponent close to the vertex point leads to a decrease in the fatigue crack propagation rate and contributes to a typical curved crack front shape. The numerical estimations of the crack shape correspond well with experimental observations taken from the literature. Further change of the stress Singularity Exponent for thin structures was studied on M(T) specimens with different thicknesses. The proposed methodology facilitates explanation of the experimentally observed decrease in the fatigue crack propagation rate (FCPR) for thin structures. It is shown, that decrease of FCPR depends on Poisson’s ratio and parameters of the Paris–Erdogan law for corresponding materials. These results can at least partially explain the effect of a free surface on fatigue crack behaviour and help towards a more reliable estimation of the residual fatigue lifetime of the structures considered.

Tomas Oplt - One of the best experts on this subject based on the ideXlab platform.

  • effect of the free surface on the fatigue crack front curvature at high stress asymmetry
    International Journal of Fatigue, 2019
    Co-Authors: Tomas Oplt, Zdeněk Chlup, Pavel Hutar, Luboš Náhlík, Pavel Pokorný, Filippo Berto
    Abstract:

    Abstract The purpose of this paper is to investigate the effect of the vertex Singularity on the fatigue crack front behaviour. Single edge notch bend specimens of steel EA4T and aluminium alloy 7075 of various thicknesses are subjected to the cyclic loading and the angles of the fatigue crack front curvature was measured. The experimental procedure is simulated using finite element analysis. Two methodologies used for the fatigue crack front shape estimation are compared. One is using stress Singularity Exponent as a controlling parameter and the second one is using stress intensity factor. Both methodologies provide comparable results of crack front formation process and they are in very good agreement with experimental results.

Martin Sevcik - One of the best experts on this subject based on the ideXlab platform.

  • numerical estimation of the fatigue crack front shape for a specimen with finite thickness
    International Journal of Fatigue, 2012
    Co-Authors: Martin Sevcik, Pavel Hutar, Michal Zouhar, Luboš Náhlík
    Abstract:

    Abstract An iterative process for the estimation of a fatigue crack front based on linear elastic fracture mechanics using values of the stress Singularity Exponent is presented. Based on the assumption of a constant stress Singularity Exponent along the crack front, a numerical approach leading to crack shape determination is suggested and applied. The crack front was approximated by a spline curve. In each node defining the crack front the stress Singularity Exponent was estimated and a complete crack front shape was found. The difference between thin and thick specimens is then described and discussed. The approach presented leads to better estimation of the crack front shape for structures with different thicknesses and a more accurate determination of fatigue crack fracture parameters. The results presented can be helpful for a better understanding of fatigue failure and more reliable prediction of residual lifetime.

  • fatigue crack shape prediction based on the stress Singularity Exponent
    Key Engineering Materials, 2011
    Co-Authors: Pavel Hutař, Martin Sevcik, Luboš Náhlík, Zdeněk Knésl
    Abstract:

    In many industrial applications it is necessary to predict fatigue lifetime of the structures where the stress field near the crack front have a three-dimensional nature. Due to the existence of vertex Singularity in the point where the crack front touches free surface, crack propagation in 3D structures cannot be reduced to a series of plane strain or plane stress problems along the crack front. The paper describes the influence of the vertex Singularity on crack shape for three-dimensional structure. The iterative process for estimation of a real crack front based on a stress Singularity Exponent is presented. In each node defining the crack front the stress Singularity Exponent has been estimated and complete crack front shape corresponding to the constant stress Singularity Exponent was found. The methodology presented can help to estimate crack front shape in a linear elastic fracture mechanics framework and estimate fracture parameters of fatigue cracks more accurately.

Zdeněk Knésl - One of the best experts on this subject based on the ideXlab platform.

  • fatigue crack shape prediction based on the stress Singularity Exponent
    Key Engineering Materials, 2011
    Co-Authors: Pavel Hutař, Martin Sevcik, Luboš Náhlík, Zdeněk Knésl
    Abstract:

    In many industrial applications it is necessary to predict fatigue lifetime of the structures where the stress field near the crack front have a three-dimensional nature. Due to the existence of vertex Singularity in the point where the crack front touches free surface, crack propagation in 3D structures cannot be reduced to a series of plane strain or plane stress problems along the crack front. The paper describes the influence of the vertex Singularity on crack shape for three-dimensional structure. The iterative process for estimation of a real crack front based on a stress Singularity Exponent is presented. In each node defining the crack front the stress Singularity Exponent has been estimated and complete crack front shape corresponding to the constant stress Singularity Exponent was found. The methodology presented can help to estimate crack front shape in a linear elastic fracture mechanics framework and estimate fracture parameters of fatigue cracks more accurately.

  • The effect of a free surface on fatigue crack behaviour
    International Journal of Fatigue, 2010
    Co-Authors: Pavel Hutař, Luboš Náhlík, Zdeněk Knésl
    Abstract:

    Abstract The effect of a free surface on fatigue crack behaviour is discussed in the paper and generalized stress intensity factor methodology is used for a reliable estimation of the fatigue crack propagation rate in the area close to a free surface, where the effect of vertex Singularity is important. It is shown that a decrease in the stress Singularity Exponent close to the vertex point leads to a decrease in the fatigue crack propagation rate and contributes to a typical curved crack front shape. The numerical estimations of the crack shape correspond well with experimental observations taken from the literature. Further change of the stress Singularity Exponent for thin structures was studied on M(T) specimens with different thicknesses. The proposed methodology facilitates explanation of the experimentally observed decrease in the fatigue crack propagation rate (FCPR) for thin structures. It is shown, that decrease of FCPR depends on Poisson’s ratio and parameters of the Paris–Erdogan law for corresponding materials. These results can at least partially explain the effect of a free surface on fatigue crack behaviour and help towards a more reliable estimation of the residual fatigue lifetime of the structures considered.