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Dimitris C Lagoudas - One of the best experts on this subject based on the ideXlab platform.

  • Stable Crack Growth During Thermal Actuation of Shape Memory Alloys
    Shape Memory and Superelasticity, 2016
    Co-Authors: S. Jape, Theocharis Baxevanis, Dimitris C Lagoudas
    Abstract:

    A finite element analysis of crack growth is carried out in shape memory alloys subjected to thermal variations under Plane Strain, Mode I, constant applied loading. The crack is assumed to propagate at a critical level of the crack-tip energy release rate which is Modeled using the virtual crack closure technique. The load level, applied at a high temperature at which the austenite phase is stable, is assumed sufficiently low so that the resulting crack-tip energy release rate is smaller than the critical value but sufficiently high so that the critical value is reached during cooling, initiating crack growth (Baxevanis and Lagoudas in Int J Fract 191:191–213, 2015 ). Stable crack growth is observed, mainly associated with the shielding effect of the transformed material left in the wake of the advancing crack. Results pertaining to the near-tip mechanical fields and fracture toughness are presented and their sensitivity to phase transformation metrics and bias load levels is investigated.

  • On the Effect of Latent Heat on the Fracture Toughness of Pseudoelastic Shape Memory Alloys
    Journal of Applied Mechanics, 2014
    Co-Authors: Theocharis Baxevanis, Chad M. Landis, Dimitris C Lagoudas
    Abstract:

    A finite element analysis of steady-state crack growth in pseudoelastic shape memory alloys under the assumption of adiabatic conditions is carried out for Plane Strain, Mode I loading. The crack is assumed to propagate at a critical level of the crack-tip energy release rate and the fracture toughness is obtained as the ratio of the far-field applied energy release rate to the crack-tip critical value. Results related to the influence of latent heat on the near-tip stress field and fracture toughness are presented for a range of parameters related to thermomechanical coupling. The levels of fracture toughness enhancement, associated with the energy dissipated by the transformed material in the wake of the growing crack, are found to be lower under adiabatic conditions than under isothermal conditions [Baxevanis et al., 2014, J. Appl. Mech., 81, 041005]. Given that in real applications of shape memory alloy (SMA) components the processes are usually not adiabatic, which is the case with the lowest energy dissipation during a cyclic loading–unloading process (hysteresis), it is expected that the actual level of transformation toughening would be higher than the one corresponding to the adiabatic case.

  • Stable crack growth during actuation in shape memory alloys
    Behavior and Mechanics of Multifunctional Materials and Composites 2014, 2014
    Co-Authors: S. Jape, Theocharis Baxevanis, Dimitris C Lagoudas
    Abstract:

    A finite element analysis of crack growth is carried out in an in nite center-cracked shape memory alloy plate subjected to thermal variations under Plane Strain Mode I constant applied loading. Crack is assumed to propagate when the energy release rate reaches a material specific critical value. The virtual crack growth technique is employed to calculate the energy release rate, which was shown to increase an order of magnitude at constant applied loading as a result of phase transformation induced by thermal variations. 1 A fracture toughening is observed associated with the energy dissipated by the transformed material in the wake of the growing crack and its sensitivity over key thermomechanical parameters is presented.

  • On the Fracture Toughness of Pseudoelastic Shape Memory Alloys
    Journal of Applied Mechanics, 2013
    Co-Authors: Theocharis Baxevanis, Chad M. Landis, Dimitris C Lagoudas
    Abstract:

    A finite element analysis of quasi-static, steady-state crack growth in pseudoelastic shape memory alloys is carried out for Plane Strain, Mode I loading. The crack is assumed to propagate at a critical level of the crack-tip energy release rate. Results pertaining to the influence of forward and reverse phase transformation on the near-tip mechanical fields and fracture toughness are presented for a range of thermomechanical parameters and temperature. The fracture toughness is obtained as the ratio of the far-field applied energy release rate to the crack-tip energy release rate. A substantial fracture toughening is observed, in accordance with experimental observations, associated with the energy dissipated by the transformed material in the wake of the growing crack. Reverse phase transformation, being a dissipative process itself, is found to increase the levels of toughness enhancement. However, higher nominal temperatures tend to reduce the toughening of an SMA alloy—although the material’s tendency to reverse transform in the wake of the advancing crack tip increases—due to the higher stress levels required for initiation of forward transformation. [DOI: 10.1115/1.4025139]

  • On the fracture toughness enhancement due to stress-induced phase transformation in shape memory alloys
    International Journal of Plasticity, 2013
    Co-Authors: Theocharis Baxevanis, Antonino Parrinello, Dimitris C Lagoudas
    Abstract:

    Abstract A finite element analysis is carried out to Model quasi-static stable crack growth in shape memory alloys under Plane Strain, Mode I loading. The small scale transformation assumption is employed in the calculations using displacement boundary conditions on a circular region that encloses the stress-induced phase transformation zone. The crack is assumed to propagate in the region of elastically-deformed, fully-transformed martensitic zone ahead of the crack tip with the crack-tip energy release rate maintained at a critical value and the analysis is accomplished using the virtual crack closure technique. Results pertaining to the influence of stress-induced phase transformation on the near-tip mechanical fields and the ratio of the far-field energy release rate to the crack-tip energy release rate are presented, showing fracture toughness enhancement in accordance with experimental observations. Moreover, the effect of plastic dissipation on the fracture resistance of SMAs is discussed.

Theocharis Baxevanis - One of the best experts on this subject based on the ideXlab platform.

  • Stable Crack Growth During Thermal Actuation of Shape Memory Alloys
    Shape Memory and Superelasticity, 2016
    Co-Authors: S. Jape, Theocharis Baxevanis, Dimitris C Lagoudas
    Abstract:

    A finite element analysis of crack growth is carried out in shape memory alloys subjected to thermal variations under Plane Strain, Mode I, constant applied loading. The crack is assumed to propagate at a critical level of the crack-tip energy release rate which is Modeled using the virtual crack closure technique. The load level, applied at a high temperature at which the austenite phase is stable, is assumed sufficiently low so that the resulting crack-tip energy release rate is smaller than the critical value but sufficiently high so that the critical value is reached during cooling, initiating crack growth (Baxevanis and Lagoudas in Int J Fract 191:191–213, 2015 ). Stable crack growth is observed, mainly associated with the shielding effect of the transformed material left in the wake of the advancing crack. Results pertaining to the near-tip mechanical fields and fracture toughness are presented and their sensitivity to phase transformation metrics and bias load levels is investigated.

  • On the Effect of Latent Heat on the Fracture Toughness of Pseudoelastic Shape Memory Alloys
    Journal of Applied Mechanics, 2014
    Co-Authors: Theocharis Baxevanis, Chad M. Landis, Dimitris C Lagoudas
    Abstract:

    A finite element analysis of steady-state crack growth in pseudoelastic shape memory alloys under the assumption of adiabatic conditions is carried out for Plane Strain, Mode I loading. The crack is assumed to propagate at a critical level of the crack-tip energy release rate and the fracture toughness is obtained as the ratio of the far-field applied energy release rate to the crack-tip critical value. Results related to the influence of latent heat on the near-tip stress field and fracture toughness are presented for a range of parameters related to thermomechanical coupling. The levels of fracture toughness enhancement, associated with the energy dissipated by the transformed material in the wake of the growing crack, are found to be lower under adiabatic conditions than under isothermal conditions [Baxevanis et al., 2014, J. Appl. Mech., 81, 041005]. Given that in real applications of shape memory alloy (SMA) components the processes are usually not adiabatic, which is the case with the lowest energy dissipation during a cyclic loading–unloading process (hysteresis), it is expected that the actual level of transformation toughening would be higher than the one corresponding to the adiabatic case.

  • Stable crack growth during actuation in shape memory alloys
    Behavior and Mechanics of Multifunctional Materials and Composites 2014, 2014
    Co-Authors: S. Jape, Theocharis Baxevanis, Dimitris C Lagoudas
    Abstract:

    A finite element analysis of crack growth is carried out in an in nite center-cracked shape memory alloy plate subjected to thermal variations under Plane Strain Mode I constant applied loading. Crack is assumed to propagate when the energy release rate reaches a material specific critical value. The virtual crack growth technique is employed to calculate the energy release rate, which was shown to increase an order of magnitude at constant applied loading as a result of phase transformation induced by thermal variations. 1 A fracture toughening is observed associated with the energy dissipated by the transformed material in the wake of the growing crack and its sensitivity over key thermomechanical parameters is presented.

  • On the Fracture Toughness of Pseudoelastic Shape Memory Alloys
    Journal of Applied Mechanics, 2013
    Co-Authors: Theocharis Baxevanis, Chad M. Landis, Dimitris C Lagoudas
    Abstract:

    A finite element analysis of quasi-static, steady-state crack growth in pseudoelastic shape memory alloys is carried out for Plane Strain, Mode I loading. The crack is assumed to propagate at a critical level of the crack-tip energy release rate. Results pertaining to the influence of forward and reverse phase transformation on the near-tip mechanical fields and fracture toughness are presented for a range of thermomechanical parameters and temperature. The fracture toughness is obtained as the ratio of the far-field applied energy release rate to the crack-tip energy release rate. A substantial fracture toughening is observed, in accordance with experimental observations, associated with the energy dissipated by the transformed material in the wake of the growing crack. Reverse phase transformation, being a dissipative process itself, is found to increase the levels of toughness enhancement. However, higher nominal temperatures tend to reduce the toughening of an SMA alloy—although the material’s tendency to reverse transform in the wake of the advancing crack tip increases—due to the higher stress levels required for initiation of forward transformation. [DOI: 10.1115/1.4025139]

  • On the fracture toughness enhancement due to stress-induced phase transformation in shape memory alloys
    International Journal of Plasticity, 2013
    Co-Authors: Theocharis Baxevanis, Antonino Parrinello, Dimitris C Lagoudas
    Abstract:

    Abstract A finite element analysis is carried out to Model quasi-static stable crack growth in shape memory alloys under Plane Strain, Mode I loading. The small scale transformation assumption is employed in the calculations using displacement boundary conditions on a circular region that encloses the stress-induced phase transformation zone. The crack is assumed to propagate in the region of elastically-deformed, fully-transformed martensitic zone ahead of the crack tip with the crack-tip energy release rate maintained at a critical value and the analysis is accomplished using the virtual crack closure technique. Results pertaining to the influence of stress-induced phase transformation on the near-tip mechanical fields and the ratio of the far-field energy release rate to the crack-tip energy release rate are presented, showing fracture toughness enhancement in accordance with experimental observations. Moreover, the effect of plastic dissipation on the fracture resistance of SMAs is discussed.

A.k. Ghosh - One of the best experts on this subject based on the ideXlab platform.

  • An insight of the structure of stress fields for stationary crack in strength mismatch weld under Plane Strain Mode-I loading – Part II: Compact tension and middle tension specimens
    International Journal of Mechanical Sciences, 2014
    Co-Authors: I.a. Khan, Vivek Bhasin, Jayanta Chattopadhyay, R. K. Singh, K. K. Vaze, A.k. Ghosh
    Abstract:

    Abstract In-service inspections of many nuclear power plants have revealed that cracks are most likely to occur in a weld or in the regions near the weld. In part-I, the problem of a stationary crack lying at the centre of a weld in a pure bending specimen SE(PB) was analysed. The detailed structure of the global plastic fields for a deep crack, under fully plastic condition, was presented. Aspects related to the state of stress at the base-weld interface were discussed. To enhance our understanding of the weld strength mismatch effects, other commonly used fracture specimens, that is, compact tension C(T) and middle tension M(T) specimens having a weld centre crack were analysed in the present investigation. The influence of weld mismatch on the structure of global stress fields (leading to plastic yielding of the ligament) as well as on the crack tip conStraint was studied. It is demonstrated that, when a crack is postulated at the centre of a weld, a family of stress fields proposed in part-I for a SE(PB) specimen is applicable to a C(T) specimen also. The studies performed in this article, along with part-I, have established that in comparison to slip line field analysis, the modified upper bound theorem is simple and more general. It is applicable to macroscopically homogeneous materials and can also account for weld mismatch effects.

  • An insight of the structure of stress fields for stationary crack in strength mismatch weld under Plane Strain Mode-I loading—Part I: Pure bending specimen
    International Journal of Mechanical Sciences, 2012
    Co-Authors: I.a. Khan, Vivek Bhasin, Jayanta Chattopadhyay, A.k. Ghosh
    Abstract:

    Abstract In-service inspections of many nuclear power plants have revealed that cracks are most likely to occur in or the regions near the weld. Interfacial cracks under elastic as well as in elastic–plastic conditions have already been extensively discussed in literature. However, the problem of crack lying at the centre of weld is less understood. Though several detailed numerical studies have been performed to investigate the influence of weld strength mismatch on crack-tip stress fields till date, however, the detailed insight of the structure of stress fields under large scale plasticity is still lacking. The present article is intended to bridge that gap. In this work, detailed structure of the global plastic fields which occur in a deeply cracked (a/W>0.3) mismatch welded pure bending specimen, under fully plastic condition, is presented. Aspects related to the state of stress at the interface of two materials are discussed. It is shown that a family of five fields proposed in this work is adequate to cover all practical cases of weld mismatch. Proposed fields were confirmed by detailed full-field finite element analyses. Excellent agreement is observed between the proposed theoretical solutions and the numerical results.

A.g. Varias - One of the best experts on this subject based on the ideXlab platform.

  • ConStraint effects during stable transient crack growth
    Computational Mechanics, 1998
    Co-Authors: A.g. Varias
    Abstract:

    The effect of plastic-flow conStraint on the field of a crack, during stable propagation within the area, covered by the plastic zone at initiation of growth, has been examined. Plane Strain, Mode I and contained yielding have been considered. The material is homogeneous with elastic-plastic behavior, described by Hook's law, J2-flow theory and isotropic hardening.

  • ConStraint effects during stable transient crack growth
    Computational Mechanics, 1998
    Co-Authors: A.g. Varias
    Abstract:

    The effect of plastic-flow conStraint on the field of a crack, during stable propagation within the area, covered by the plastic zone at initiation of growth, has been examined. Plane Strain, Mode I and contained yielding have been considered. The material is homogeneous with elastic-plastic behavior, described by Hook's law, J _2-flow theory and isotropic hardening. The numerical investigation has been performed within the framework of a boundary layer formulation, whereby the remote loading is fully specified by the first two terms in Williams' expansion, characterized by K and T . It is shown, that a self-similar state is reached, after growth of the order of the fracture process zone size at initiation. The characteristic length of the self-similar field is the fracture process zone size. Under contained yielding, the self-similar field depends on an appropriately normalized T / K ratio, which is a measure of the deviation of the stress field from small scale yielding distribution at distances of the order of the damage process zone size. According to the analysis, the effect of conStraint on near-tip triaxiality, during transient growth is Moderate. Also the effect of conStraint on crack growth resistance is weak at initiation and increases with crack propagation.

I.a. Khan - One of the best experts on this subject based on the ideXlab platform.

  • An insight of the structure of stress fields for stationary crack in strength mismatch weld under Plane Strain Mode-I loading – Part II: Compact tension and middle tension specimens
    International Journal of Mechanical Sciences, 2014
    Co-Authors: I.a. Khan, Vivek Bhasin, Jayanta Chattopadhyay, R. K. Singh, K. K. Vaze, A.k. Ghosh
    Abstract:

    Abstract In-service inspections of many nuclear power plants have revealed that cracks are most likely to occur in a weld or in the regions near the weld. In part-I, the problem of a stationary crack lying at the centre of a weld in a pure bending specimen SE(PB) was analysed. The detailed structure of the global plastic fields for a deep crack, under fully plastic condition, was presented. Aspects related to the state of stress at the base-weld interface were discussed. To enhance our understanding of the weld strength mismatch effects, other commonly used fracture specimens, that is, compact tension C(T) and middle tension M(T) specimens having a weld centre crack were analysed in the present investigation. The influence of weld mismatch on the structure of global stress fields (leading to plastic yielding of the ligament) as well as on the crack tip conStraint was studied. It is demonstrated that, when a crack is postulated at the centre of a weld, a family of stress fields proposed in part-I for a SE(PB) specimen is applicable to a C(T) specimen also. The studies performed in this article, along with part-I, have established that in comparison to slip line field analysis, the modified upper bound theorem is simple and more general. It is applicable to macroscopically homogeneous materials and can also account for weld mismatch effects.

  • An insight of the structure of stress fields for stationary crack in strength mismatch weld under Plane Strain Mode-I loading—Part I: Pure bending specimen
    International Journal of Mechanical Sciences, 2012
    Co-Authors: I.a. Khan, Vivek Bhasin, Jayanta Chattopadhyay, A.k. Ghosh
    Abstract:

    Abstract In-service inspections of many nuclear power plants have revealed that cracks are most likely to occur in or the regions near the weld. Interfacial cracks under elastic as well as in elastic–plastic conditions have already been extensively discussed in literature. However, the problem of crack lying at the centre of weld is less understood. Though several detailed numerical studies have been performed to investigate the influence of weld strength mismatch on crack-tip stress fields till date, however, the detailed insight of the structure of stress fields under large scale plasticity is still lacking. The present article is intended to bridge that gap. In this work, detailed structure of the global plastic fields which occur in a deeply cracked (a/W>0.3) mismatch welded pure bending specimen, under fully plastic condition, is presented. Aspects related to the state of stress at the interface of two materials are discussed. It is shown that a family of five fields proposed in this work is adequate to cover all practical cases of weld mismatch. Proposed fields were confirmed by detailed full-field finite element analyses. Excellent agreement is observed between the proposed theoretical solutions and the numerical results.