The Experts below are selected from a list of 24981 Experts worldwide ranked by ideXlab platform

E A Patterson - One of the best experts on this subject based on the ideXlab platform.

  • local crack plasticity and its influences on the global Elastic Stress Field
    International Journal of Fatigue, 2013
    Co-Authors: M.n. James, E A Patterson, Colin Christopher
    Abstract:

    Abstract This paper presents the background and development of a novel ‘plastic inclusion’ approach for dealing with the local plasticity which occurs at the tip of a growing fatigue crack. Localised plasticity arises from crack growth mechanisms and essentially blunts the crack, creates a reversed cyclic plastic zone, and induces shear along the crack flanks, along with the possible generation of wake contact Stresses which act on the applied Elastic Stress Field at the boundary of the Elastic–plastic enclave surrounding the crack. The paper outlines the development of a meso-scale model of the Elastic Stress Field around a growing crack that explicitly incorporates these interaction effects. The outcome is a modified crack tip Stress intensity factor that includes some aspects of the magnitude of plastic wake-induced crack tip shielding and which the authors propose has the potential to help resolve some long-standing controversies associated with plasticity-induced closure. A full-Field approach is developed for Stress using photoElasticity and also for displacement using digital image correlation.

  • a quantitative evaluation of fatigue crack shielding forces using photoElasticity
    Engineering Fracture Mechanics, 2008
    Co-Authors: Colin Christopher, M.n. James, E A Patterson, Kong Tee
    Abstract:

    The mechanisms controlling the phenomenon of plasticity-induced shielding during fatigue are investigated and quantified by fitting a recently developed model to photoElastic data. The model derives from the Muskhelishvili approach and includes additional terms to describe the effect of plasticity on the Elastic Stress Field around the crack tip. The photoElastic technique used a polycarbonate CT specimen containing a naturally propagating fatigue crack from which full-Field data was obtained digitally using the phase-stepping method. The model was fitted to approximately 1000 data values for the isochromatic fringe order around the crack tip and generated values for the Stress intensity factor and T-Stress plus an interfacial shear Stress intensity factor and a retardation intensity factor which together characterize the influence of plasticity on crack growth.

  • on determining Stress intensity factors for mixed mode cracks from thermoElastic data
    Fatigue & Fracture of Engineering Materials & Structures, 1997
    Co-Authors: R A Tomlinson, Andrew D Nurse, E A Patterson
    Abstract:

    — An alternative methodology is presented for determining Stress intensity factors for cracks subject to mixed-mode displacements. The methodology involves thermoElastic data generated from a SPATE (Stress Pattern Analysis by Thermal Emission) system and has been adapted from one used successfully in photoElasticity. The thermoElastic data is collected throughout the Elastic Stress Field dominated by the crack tip singularity. The Stress Field is described using a Fourier series within Muskhelishvili's approach. This method allows different applied Stress Fields to be described which may include transient or non-uniform Stress Fields. The results obtained using the new methodology are at least as good as those obtained previously for pure mode I cases, and generally better for mixed mode displacement conditions.

M.n. James - One of the best experts on this subject based on the ideXlab platform.

  • local crack plasticity and its influences on the global Elastic Stress Field
    International Journal of Fatigue, 2013
    Co-Authors: M.n. James, E A Patterson, Colin Christopher
    Abstract:

    Abstract This paper presents the background and development of a novel ‘plastic inclusion’ approach for dealing with the local plasticity which occurs at the tip of a growing fatigue crack. Localised plasticity arises from crack growth mechanisms and essentially blunts the crack, creates a reversed cyclic plastic zone, and induces shear along the crack flanks, along with the possible generation of wake contact Stresses which act on the applied Elastic Stress Field at the boundary of the Elastic–plastic enclave surrounding the crack. The paper outlines the development of a meso-scale model of the Elastic Stress Field around a growing crack that explicitly incorporates these interaction effects. The outcome is a modified crack tip Stress intensity factor that includes some aspects of the magnitude of plastic wake-induced crack tip shielding and which the authors propose has the potential to help resolve some long-standing controversies associated with plasticity-induced closure. A full-Field approach is developed for Stress using photoElasticity and also for displacement using digital image correlation.

  • a quantitative evaluation of fatigue crack shielding forces using photoElasticity
    Engineering Fracture Mechanics, 2008
    Co-Authors: Colin Christopher, M.n. James, E A Patterson, Kong Tee
    Abstract:

    The mechanisms controlling the phenomenon of plasticity-induced shielding during fatigue are investigated and quantified by fitting a recently developed model to photoElastic data. The model derives from the Muskhelishvili approach and includes additional terms to describe the effect of plasticity on the Elastic Stress Field around the crack tip. The photoElastic technique used a polycarbonate CT specimen containing a naturally propagating fatigue crack from which full-Field data was obtained digitally using the phase-stepping method. The model was fitted to approximately 1000 data values for the isochromatic fringe order around the crack tip and generated values for the Stress intensity factor and T-Stress plus an interfacial shear Stress intensity factor and a retardation intensity factor which together characterize the influence of plasticity on crack growth.

Xiaoping Zhou - One of the best experts on this subject based on the ideXlab platform.

  • the zonal disintegration mechanism of surrounding rock around deep spherical tunnels under hydrostatic pressure condition a non euclidean continuum damage model
    Acta Mechanica Solida Sinica, 2013
    Co-Authors: Xiaoping Zhou, Qihu Qian, Qinghong Hou, Yongxing Zhang
    Abstract:

    A new non-Euclidean continuum damage model is proposed to investigate the zonal disintegration phenomenon of the surrounding rocks around deep spherical tunnels under hydrostatic pressure condition as well as the total Elastic Stress Field distributions. The Elastic Stress Fields of the surrounding rocks around deep spherical tunnels under hydrostatic pressure condition are obtained. If the Elastic Stresses of the surrounding rocks satisfy the strength criterion of the deep rock masses, the number, size and location of fractured and nonfractured zones are determined. The effect of physico-mechanical parameters of the surrounding rocks on the zonal disintegration phenomenon is studied and numerical computation is carried out. It is found from numerical results that the number, size and location of fractured and non-fractured zones are sensitive to the physico-mechanical parameters of the surrounding rocks.

  • zonal disintegration mechanism of cross anisotropic rock masses around a deep circular tunnel
    Theoretical and Applied Fracture Mechanics, 2012
    Co-Authors: Xiaoping Zhou, G Chen, Q H Qian
    Abstract:

    Abstract The zonal disintegration phenomenon is investigated for cross-anisotropic rock around a deep circular tunnel under hydrostatic pressure condition as well as the total Elastic Stress-Field distributions. The number and size of fractured and non-fractured zones is determined by using the Mohr–Coulomb criterion. Effects of cross-anisotropic Elastic parameters of deep rock mass on the zonal disintegration phenomenon are investigated. Numerical computations are carried out. It is shown from numerical results that the number and size of fractured and non-fractured zones significantly depend on to cross-anisotropic Elastic parameters of deep rock mass.

  • non euclidean continuum model of the zonal disintegration of surrounding rocks around a deep circular tunnel in a non hydrostatic pressure state
    Journal of Mining Science, 2011
    Co-Authors: Qihu Qian, Xiaoping Zhou
    Abstract:

    A non-Euclidean continuum model for the descriptions of the Elastic Stress-Field distributions and fractured zones in the surrounding rock masses around the deep circular tunnels subjected to nonhydrostatic pressure are established. In the non-Euclidean continuum model, the Elastic Stress-Field distribution of the deep surrounding rock induced by compatible deformation of non-fractured zones and incompatible deformation of fractured zones is determined. The wavy behavior of the Stress components based on the non-Euclidean model are obviously different from that of the Stress components which have extrema on the working contour and tend monotonically to the value of the in-situ Stress at infinity in rock masses within the framework of the classical model. Mohr-Coulomb criterion is applied to research the occurrence of disintegration zones. Disintegration zones appear when the Stresses in deep rock masses reach a certain critical value. It is found from the numerical results that the magnitude and site of fractured zones depend on the value of in-situ Stress and non-Euclideanness parameters.

Yujin Hu - One of the best experts on this subject based on the ideXlab platform.

  • free vibration analysis of nonlocal strain gradient beams made of functionally graded material
    International Journal of Engineering Science, 2016
    Co-Authors: Li Li, Xiaobai Li, Yujin Hu
    Abstract:

    Abstract A size-dependent Timoshenko beam model, which accounts for through-thickness power-law variation of a two-constituent functionally graded (FG) material, is derived in the framework of the nonlocal strain gradient theory. The equations of motion and boundary conditions are deduced by employing the Hamilton principle. The model contains a material length scale parameter introduced to consider the significance of strain gradient Stress Field and a nonlocal parameter introduced to consider the significance of nonlocal Elastic Stress Field. The influence of through-thickness power-law variation and size-dependent parameters on vibration is investigated. It is found that through-thickness grading of the FG material in the beam has a great effect on the natural frequencies and therefore can be used to control the natural frequencies. The vibration frequencies can generally increase with the increasing material length scale parameter or the decreasing nonlocal parameter. When the material characteristic parameter is smaller than the nonlocal parameter, the FG beam exerts a stiffness-softening effect. When the material characteristic parameter is larger than the nonlocal parameter, the FG beam exerts a stiffness-hardening effect.

  • flexural wave propagation in small scaled functionally graded beams via a nonlocal strain gradient theory
    Composite Structures, 2015
    Co-Authors: Li Li, Yujin Hu, Ling Ling
    Abstract:

    Abstract An analytic model of small-scaled functionally graded (FG) beams for the flexural wave propagation analysis is developed based on the nonlocal strain gradient theory, in which the Stress accounts for not only the nonlocal Elastic Stress Field but also the strain gradients Stress Field. By using the analytic model, the acoustical and optical dispersion relations between phase velocity and wave number are explicitly derived. It is found that an asymptotic phase velocity of both the acoustical and optical branches can be observed. The asymptotic phase velocity can be increased by decreasing the nonlocal parameter or increasing the material characteristic parameter. Furthermore, the power-law index has a significant effect on the acoustical and optical dispersion relations of nano-scaled FG beams. The effects of nonlocal parameter and material characteristic parameter on the acoustical and optical dispersion relation are significant at high wave numbers, however, may be ignored at low wave numbers. The acoustical and optical phase velocities can generally increase with the increasing material length scale parameter or the decreasing nonlocal parameter.

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

  • free vibration analysis of nonlocal strain gradient beams made of functionally graded material
    International Journal of Engineering Science, 2016
    Co-Authors: Li Li, Xiaobai Li, Yujin Hu
    Abstract:

    Abstract A size-dependent Timoshenko beam model, which accounts for through-thickness power-law variation of a two-constituent functionally graded (FG) material, is derived in the framework of the nonlocal strain gradient theory. The equations of motion and boundary conditions are deduced by employing the Hamilton principle. The model contains a material length scale parameter introduced to consider the significance of strain gradient Stress Field and a nonlocal parameter introduced to consider the significance of nonlocal Elastic Stress Field. The influence of through-thickness power-law variation and size-dependent parameters on vibration is investigated. It is found that through-thickness grading of the FG material in the beam has a great effect on the natural frequencies and therefore can be used to control the natural frequencies. The vibration frequencies can generally increase with the increasing material length scale parameter or the decreasing nonlocal parameter. When the material characteristic parameter is smaller than the nonlocal parameter, the FG beam exerts a stiffness-softening effect. When the material characteristic parameter is larger than the nonlocal parameter, the FG beam exerts a stiffness-hardening effect.

  • flexural wave propagation in small scaled functionally graded beams via a nonlocal strain gradient theory
    Composite Structures, 2015
    Co-Authors: Li Li, Yujin Hu, Ling Ling
    Abstract:

    Abstract An analytic model of small-scaled functionally graded (FG) beams for the flexural wave propagation analysis is developed based on the nonlocal strain gradient theory, in which the Stress accounts for not only the nonlocal Elastic Stress Field but also the strain gradients Stress Field. By using the analytic model, the acoustical and optical dispersion relations between phase velocity and wave number are explicitly derived. It is found that an asymptotic phase velocity of both the acoustical and optical branches can be observed. The asymptotic phase velocity can be increased by decreasing the nonlocal parameter or increasing the material characteristic parameter. Furthermore, the power-law index has a significant effect on the acoustical and optical dispersion relations of nano-scaled FG beams. The effects of nonlocal parameter and material characteristic parameter on the acoustical and optical dispersion relation are significant at high wave numbers, however, may be ignored at low wave numbers. The acoustical and optical phase velocities can generally increase with the increasing material length scale parameter or the decreasing nonlocal parameter.