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Jan Klusak - One of the best experts on this subject based on the ideXlab platform.

  • Multi-parameter average strain energy density factor criterion applied on the sharp Material Inclusion problem
    Procedia structural integrity, 2018
    Co-Authors: Ondrej Krepl, Jan Klusak
    Abstract:

    Abstract The tip of a sharp Material Inclusion (SMI) embedded in a parent Material is considered as the singular stress concentrator. The SMI tip is modelled as a special case of a multi-Material junction. The singular stress behaviour is caused by the Material mismatch and geometrical discontinuity. The power of singularity is lower in comparison to the case of a crack. The stress field can be described by the asymptotic stress series, in which each term contains generalized stress intensity factor and stress terms exponent. The exponents are determined as a solution of eigenvalue problem. The factors are calculated by combination of analytical and numerical approaches. The terms can be either singular or non-singular depending on the stress term exponent. When approaching the concentrator, the singular terms become unbounded while the non-singular terms vanish. The non-singular terms increase precision of stress description on larger distances from the point of singularity. In some cases they provide the only means to describe the stress field well. Because of the singular stress behaviour near SMI tip, this location is prone to crack initiation. The crack initiation conditions are calculated by the average strain energy density factor (SEDF) criterion. Contrary to the case of a crack, the direction of minimum of SEDF changes with distance from the singular point. Therefore, an averaged value over specific distance is used. If the specific distance is relatively large, the employment of non-singular terms in multi-parameter criterion can significantly improve the critical parameters prediction. Thanks to that e.g. the particle composite design can be optimized.

  • crack onset assessment near the sharp Material Inclusion tip by means of modified maximum tangential stress criterion
    Fracture and Structural Integrity, 2017
    Co-Authors: Ondrej Krepl, Jan Klusak
    Abstract:

    In the case of particle reinforced composites, where the particles are in a form of sharp Material Inclusions, singular stress concentration exists on each tip of each Inclusion. This is due to the geometric and Material discontinuities between matrix and particle. These points of stress concentration are susceptible of crack initiation and thus often responsible for failure of the whole structure. The modified maximum tangential stress criterion is employed in order to predict crack onset conditions.

  • the influence of non singular terms on the precision of stress description near a sharp Material Inclusion tip
    Theoretical and Applied Fracture Mechanics, 2017
    Co-Authors: Ondrej Krepl, Jan Klusak
    Abstract:

    Abstract A theoretical elastic stress field in the vicinity of a sharp Material Inclusion tip has a singular character. The power of a stress singularity, characterized by the exponents of the singularity, is different from the power of a singularity in the case of a crack in homogenous media. Stress distribution near the singular point can be described by an asymptotic expansion. The series consists of singular and non-singular terms, depending on the eigenvalue λ in the exponent of each term. The singular terms are characterized by 0 R ( λ ) 1 , while the relation 1 R ( λ ) applies to non-singular terms. A sharp Material Inclusion is modelled as a special case of a multi-Material junction, a bi-Material junction. A method to calculate eigenvalues for a problem of a bi-Material junction of given boundary conditions is described. Then based on the knowledge of eigenvectors, the eigenfunctions can be formed and Generalized Stress Intensity Factors (GSIFs) obtained by the Overdeterministic Method (ODM). The ODM returns GSIFs as a least square solution of a system of linear equations, which consists of analytical relations and a large amount of Finite Element Method (FEM) displacement results. In the majority of fracture mechanics analyses of cracks and notches, only the singular terms are considered to assess the stability of these general singular stress concentrators. This article presents results for four bi-Material combinations of a sharp Inclusion and a matrix in the form of stress plots. Stress plots show an analytical solution with the use of (i) singular terms, and (ii) singular and non-singular terms. Analytical solutions are then compared to pure FEM results. Further, the absolute and relative errors between both cases of analytical description and an FEM solution are calculated and plotted. The effect of an elastic moduli mismatch and the distance from the Inclusion tip is investigated and quantified by mean absolute error of tangential stress.

  • Multi-Parameter Based Stress Distribution in Vicinity of Sharp Material Inclusion Tip
    Solid State Phenomena, 2016
    Co-Authors: Ondrej Krepl, Jan Klusak
    Abstract:

    General Singular Stress Concentrators (GSSCs) which exhibit singular stress concentration are often responsible for crack initiation and thus failure of the component. The GSSC of the type of bonded bi-Material junction occurs in a variety of technical applications including but not limited to sharp Material Inclusions, silicate based composites and electronic components. The GSSC cannot be assessed by means of standard fracture mechanics. Approaches of generalized fracture mechanics require precise description of stress distribution near the stress concentration points. In order to determine the stress field accurately, the paper incorporates the multi-parameter based description.

  • reconstruction of a 2d stress field around the tip of a sharp Material Inclusion
    Procedia structural integrity, 2016
    Co-Authors: Ondrej Krepl, Jan Klusak
    Abstract:

    Abstract The stress distribution in the vicinity of a sharp Material Inclusion (SMI) tip exhibits a singular stress behavior. The strength of the stress singularity depends on Material properties and geometry. The SMI is a special case of a general singular stress concentrator (GSSC). The stress field near a GSSC can be analytically described by means of Muskhelishvili plane elasticity based on complex variable function methods. Parameters necessary for the description are the exponents of singularity and generalized stress intensity factors (GSIFs). The stress field in the closest vicinity of an SMI tip is thus characterized by 1 or 2 singular exponents (λ-1), for which 0

Vasilios Bakolas - One of the best experts on this subject based on the ideXlab platform.

  • Material Inclusion Factors for Lundberg-Palmgren–Based RCF Life Equations
    Tribology Transactions, 2011
    Co-Authors: Behrooz Jalalahmadi, Farshid Sadeghi, Vasilios Bakolas
    Abstract:

    Material Inclusions in the form of hydrogen embrittlement, carbides, etc., are by-products of manufacturing processes and commonly present in bearing steel. The objective of this study was to develop a life equation for rolling contact fatigue phenomenon that accounts for the effects of Inclusions. The life equation was developed using the fatigue results previously obtained using the damage model (Jalalahmadi and Sadeghi, Journal of Tribology vol. 132, 2010). Four modifying factors counting for effects of the stiffness, size, depth, and number of the Inclusions are used to modify the life equation. These modifying coefficients are extracted from the simulations obtained from the Voronoi Finite element (FE) model and the Lundberg-Palmgren-based fatigue criterion (Jalalahmadi and Sadeghi, Journal of Tribology vol. 131, 2009). These simulations predict Weibull slopes and L 10 lives that are in good agreement with the previous theoretical and experimental results. It is seen that as Inclusions become larger ...

  • Material Inclusion factors for lundberg palmgren based rcf life equations
    Tribology Transactions, 2011
    Co-Authors: Behrooz Jalalahmadi, Farshid Sadeghi, Vasilios Bakolas
    Abstract:

    Material Inclusions in the form of hydrogen embrittlement, carbides, etc., are by-products of manufacturing processes and commonly present in bearing steel. The objective of this study was to develop a life equation for rolling contact fatigue phenomenon that accounts for the effects of Inclusions. The life equation was developed using the fatigue results previously obtained using the damage model (Jalalahmadi and Sadeghi, Journal of Tribology vol. 132, 2010). Four modifying factors counting for effects of the stiffness, size, depth, and number of the Inclusions are used to modify the life equation. These modifying coefficients are extracted from the simulations obtained from the Voronoi Finite element (FE) model and the Lundberg-Palmgren-based fatigue criterion (Jalalahmadi and Sadeghi, Journal of Tribology vol. 131, 2009). These simulations predict Weibull slopes and L 10 lives that are in good agreement with the previous theoretical and experimental results. It is seen that as Inclusions become larger ...

  • Material Inclusion Factors for Lundberg-Palmgren–Based RCF Life Equations
    Tribology Transactions, 2011
    Co-Authors: Behrooz Jalalahmadi, Farshid Sadeghi, Vasilios Bakolas
    Abstract:

    Material Inclusions in the form of hydrogen embrittlement, carbides, etc., are by-products of manufacturing processes and commonly present in bearing steel. The objective of this study was to develop a life equation for rolling contact fatigue phenomenon that accounts for the effects of Inclusions. The life equation was developed using the fatigue results previously obtained using the damage model (Jalalahmadi and Sadeghi, Journal of Tribology vol. 132, 2010). Four modifying factors counting for effects of the stiffness, size, depth, and number of the Inclusions are used to modify the life equation. These modifying coefficients are extracted from the simulations obtained from the Voronoi Finite element (FE) model and the Lundberg-Palmgren-based fatigue criterion (Jalalahmadi and Sadeghi, Journal of Tribology vol. 131, 2009). These simulations predict Weibull slopes and L10 lives that are in good agreement with the previous theoretical and experimental results. It is seen that as Inclusions become larger or shallower, they cause a larger decrease in the fatigue lives and their scatter. Also, introduction of more Inclusions to the Material significantly reduces the fatigue lives and their Weibull slopes.

Ondrej Krepl - One of the best experts on this subject based on the ideXlab platform.

  • Multi-parameter average strain energy density factor criterion applied on the sharp Material Inclusion problem
    Procedia structural integrity, 2018
    Co-Authors: Ondrej Krepl, Jan Klusak
    Abstract:

    Abstract The tip of a sharp Material Inclusion (SMI) embedded in a parent Material is considered as the singular stress concentrator. The SMI tip is modelled as a special case of a multi-Material junction. The singular stress behaviour is caused by the Material mismatch and geometrical discontinuity. The power of singularity is lower in comparison to the case of a crack. The stress field can be described by the asymptotic stress series, in which each term contains generalized stress intensity factor and stress terms exponent. The exponents are determined as a solution of eigenvalue problem. The factors are calculated by combination of analytical and numerical approaches. The terms can be either singular or non-singular depending on the stress term exponent. When approaching the concentrator, the singular terms become unbounded while the non-singular terms vanish. The non-singular terms increase precision of stress description on larger distances from the point of singularity. In some cases they provide the only means to describe the stress field well. Because of the singular stress behaviour near SMI tip, this location is prone to crack initiation. The crack initiation conditions are calculated by the average strain energy density factor (SEDF) criterion. Contrary to the case of a crack, the direction of minimum of SEDF changes with distance from the singular point. Therefore, an averaged value over specific distance is used. If the specific distance is relatively large, the employment of non-singular terms in multi-parameter criterion can significantly improve the critical parameters prediction. Thanks to that e.g. the particle composite design can be optimized.

  • the influence of non singular terms on the precision of stress description near a sharp Material Inclusion tip
    Theoretical and Applied Fracture Mechanics, 2017
    Co-Authors: Ondrej Krepl, Jan Klusak
    Abstract:

    Abstract A theoretical elastic stress field in the vicinity of a sharp Material Inclusion tip has a singular character. The power of a stress singularity, characterized by the exponents of the singularity, is different from the power of a singularity in the case of a crack in homogenous media. Stress distribution near the singular point can be described by an asymptotic expansion. The series consists of singular and non-singular terms, depending on the eigenvalue λ in the exponent of each term. The singular terms are characterized by 0 R ( λ ) 1 , while the relation 1 R ( λ ) applies to non-singular terms. A sharp Material Inclusion is modelled as a special case of a multi-Material junction, a bi-Material junction. A method to calculate eigenvalues for a problem of a bi-Material junction of given boundary conditions is described. Then based on the knowledge of eigenvectors, the eigenfunctions can be formed and Generalized Stress Intensity Factors (GSIFs) obtained by the Overdeterministic Method (ODM). The ODM returns GSIFs as a least square solution of a system of linear equations, which consists of analytical relations and a large amount of Finite Element Method (FEM) displacement results. In the majority of fracture mechanics analyses of cracks and notches, only the singular terms are considered to assess the stability of these general singular stress concentrators. This article presents results for four bi-Material combinations of a sharp Inclusion and a matrix in the form of stress plots. Stress plots show an analytical solution with the use of (i) singular terms, and (ii) singular and non-singular terms. Analytical solutions are then compared to pure FEM results. Further, the absolute and relative errors between both cases of analytical description and an FEM solution are calculated and plotted. The effect of an elastic moduli mismatch and the distance from the Inclusion tip is investigated and quantified by mean absolute error of tangential stress.

  • Multi-Parameter Based Stress Distribution in Vicinity of Sharp Material Inclusion Tip
    Solid State Phenomena, 2016
    Co-Authors: Ondrej Krepl, Jan Klusak
    Abstract:

    General Singular Stress Concentrators (GSSCs) which exhibit singular stress concentration are often responsible for crack initiation and thus failure of the component. The GSSC of the type of bonded bi-Material junction occurs in a variety of technical applications including but not limited to sharp Material Inclusions, silicate based composites and electronic components. The GSSC cannot be assessed by means of standard fracture mechanics. Approaches of generalized fracture mechanics require precise description of stress distribution near the stress concentration points. In order to determine the stress field accurately, the paper incorporates the multi-parameter based description.

  • Reconstruction of 2D stress field around a tip of sharp Material Inclusion
    2016
    Co-Authors: Ondrej Krepl
    Abstract:

    A stress distribution in vicinity of the Sharp Material Inclusion (SMI) tip exhibits a singular stress behavior. The strength of stress singularity is Material properties and geometry dependent. The SMI is a special case of general singular stress concentrator. A stress field near the general singular stress concentrator can be analytically described by means of Muskhelishvili plane elasticity based on complex variable functions. Parameters necessary for the description are the exponents of singularity and Generalized Stress Intensity Factors (GSIFs). The stress field in the closest vicinity of the SMI tip is thus characterized by 1 or 2 singular exponents, 0

  • reconstruction of a 2d stress field around the tip of a sharp Material Inclusion
    Procedia structural integrity, 2016
    Co-Authors: Ondrej Krepl, Jan Klusak
    Abstract:

    Abstract The stress distribution in the vicinity of a sharp Material Inclusion (SMI) tip exhibits a singular stress behavior. The strength of the stress singularity depends on Material properties and geometry. The SMI is a special case of a general singular stress concentrator (GSSC). The stress field near a GSSC can be analytically described by means of Muskhelishvili plane elasticity based on complex variable function methods. Parameters necessary for the description are the exponents of singularity and generalized stress intensity factors (GSIFs). The stress field in the closest vicinity of an SMI tip is thus characterized by 1 or 2 singular exponents (λ-1), for which 0

Behrooz Jalalahmadi - One of the best experts on this subject based on the ideXlab platform.

  • Material Inclusion Factors for Lundberg-Palmgren–Based RCF Life Equations
    Tribology Transactions, 2011
    Co-Authors: Behrooz Jalalahmadi, Farshid Sadeghi, Vasilios Bakolas
    Abstract:

    Material Inclusions in the form of hydrogen embrittlement, carbides, etc., are by-products of manufacturing processes and commonly present in bearing steel. The objective of this study was to develop a life equation for rolling contact fatigue phenomenon that accounts for the effects of Inclusions. The life equation was developed using the fatigue results previously obtained using the damage model (Jalalahmadi and Sadeghi, Journal of Tribology vol. 132, 2010). Four modifying factors counting for effects of the stiffness, size, depth, and number of the Inclusions are used to modify the life equation. These modifying coefficients are extracted from the simulations obtained from the Voronoi Finite element (FE) model and the Lundberg-Palmgren-based fatigue criterion (Jalalahmadi and Sadeghi, Journal of Tribology vol. 131, 2009). These simulations predict Weibull slopes and L 10 lives that are in good agreement with the previous theoretical and experimental results. It is seen that as Inclusions become larger ...

  • Material Inclusion factors for lundberg palmgren based rcf life equations
    Tribology Transactions, 2011
    Co-Authors: Behrooz Jalalahmadi, Farshid Sadeghi, Vasilios Bakolas
    Abstract:

    Material Inclusions in the form of hydrogen embrittlement, carbides, etc., are by-products of manufacturing processes and commonly present in bearing steel. The objective of this study was to develop a life equation for rolling contact fatigue phenomenon that accounts for the effects of Inclusions. The life equation was developed using the fatigue results previously obtained using the damage model (Jalalahmadi and Sadeghi, Journal of Tribology vol. 132, 2010). Four modifying factors counting for effects of the stiffness, size, depth, and number of the Inclusions are used to modify the life equation. These modifying coefficients are extracted from the simulations obtained from the Voronoi Finite element (FE) model and the Lundberg-Palmgren-based fatigue criterion (Jalalahmadi and Sadeghi, Journal of Tribology vol. 131, 2009). These simulations predict Weibull slopes and L 10 lives that are in good agreement with the previous theoretical and experimental results. It is seen that as Inclusions become larger ...

  • Material Inclusion Factors for Lundberg-Palmgren–Based RCF Life Equations
    Tribology Transactions, 2011
    Co-Authors: Behrooz Jalalahmadi, Farshid Sadeghi, Vasilios Bakolas
    Abstract:

    Material Inclusions in the form of hydrogen embrittlement, carbides, etc., are by-products of manufacturing processes and commonly present in bearing steel. The objective of this study was to develop a life equation for rolling contact fatigue phenomenon that accounts for the effects of Inclusions. The life equation was developed using the fatigue results previously obtained using the damage model (Jalalahmadi and Sadeghi, Journal of Tribology vol. 132, 2010). Four modifying factors counting for effects of the stiffness, size, depth, and number of the Inclusions are used to modify the life equation. These modifying coefficients are extracted from the simulations obtained from the Voronoi Finite element (FE) model and the Lundberg-Palmgren-based fatigue criterion (Jalalahmadi and Sadeghi, Journal of Tribology vol. 131, 2009). These simulations predict Weibull slopes and L10 lives that are in good agreement with the previous theoretical and experimental results. It is seen that as Inclusions become larger or shallower, they cause a larger decrease in the fatigue lives and their scatter. Also, introduction of more Inclusions to the Material significantly reduces the fatigue lives and their Weibull slopes.

Farshid Sadeghi - One of the best experts on this subject based on the ideXlab platform.

  • Material Inclusion Factors for Lundberg-Palmgren–Based RCF Life Equations
    Tribology Transactions, 2011
    Co-Authors: Behrooz Jalalahmadi, Farshid Sadeghi, Vasilios Bakolas
    Abstract:

    Material Inclusions in the form of hydrogen embrittlement, carbides, etc., are by-products of manufacturing processes and commonly present in bearing steel. The objective of this study was to develop a life equation for rolling contact fatigue phenomenon that accounts for the effects of Inclusions. The life equation was developed using the fatigue results previously obtained using the damage model (Jalalahmadi and Sadeghi, Journal of Tribology vol. 132, 2010). Four modifying factors counting for effects of the stiffness, size, depth, and number of the Inclusions are used to modify the life equation. These modifying coefficients are extracted from the simulations obtained from the Voronoi Finite element (FE) model and the Lundberg-Palmgren-based fatigue criterion (Jalalahmadi and Sadeghi, Journal of Tribology vol. 131, 2009). These simulations predict Weibull slopes and L 10 lives that are in good agreement with the previous theoretical and experimental results. It is seen that as Inclusions become larger ...

  • Material Inclusion factors for lundberg palmgren based rcf life equations
    Tribology Transactions, 2011
    Co-Authors: Behrooz Jalalahmadi, Farshid Sadeghi, Vasilios Bakolas
    Abstract:

    Material Inclusions in the form of hydrogen embrittlement, carbides, etc., are by-products of manufacturing processes and commonly present in bearing steel. The objective of this study was to develop a life equation for rolling contact fatigue phenomenon that accounts for the effects of Inclusions. The life equation was developed using the fatigue results previously obtained using the damage model (Jalalahmadi and Sadeghi, Journal of Tribology vol. 132, 2010). Four modifying factors counting for effects of the stiffness, size, depth, and number of the Inclusions are used to modify the life equation. These modifying coefficients are extracted from the simulations obtained from the Voronoi Finite element (FE) model and the Lundberg-Palmgren-based fatigue criterion (Jalalahmadi and Sadeghi, Journal of Tribology vol. 131, 2009). These simulations predict Weibull slopes and L 10 lives that are in good agreement with the previous theoretical and experimental results. It is seen that as Inclusions become larger ...

  • Material Inclusion Factors for Lundberg-Palmgren–Based RCF Life Equations
    Tribology Transactions, 2011
    Co-Authors: Behrooz Jalalahmadi, Farshid Sadeghi, Vasilios Bakolas
    Abstract:

    Material Inclusions in the form of hydrogen embrittlement, carbides, etc., are by-products of manufacturing processes and commonly present in bearing steel. The objective of this study was to develop a life equation for rolling contact fatigue phenomenon that accounts for the effects of Inclusions. The life equation was developed using the fatigue results previously obtained using the damage model (Jalalahmadi and Sadeghi, Journal of Tribology vol. 132, 2010). Four modifying factors counting for effects of the stiffness, size, depth, and number of the Inclusions are used to modify the life equation. These modifying coefficients are extracted from the simulations obtained from the Voronoi Finite element (FE) model and the Lundberg-Palmgren-based fatigue criterion (Jalalahmadi and Sadeghi, Journal of Tribology vol. 131, 2009). These simulations predict Weibull slopes and L10 lives that are in good agreement with the previous theoretical and experimental results. It is seen that as Inclusions become larger or shallower, they cause a larger decrease in the fatigue lives and their scatter. Also, introduction of more Inclusions to the Material significantly reduces the fatigue lives and their Weibull slopes.