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

  • Strain Dependent Stiffness of plasma sprayed thermal barrier coatings
    Surface and Coatings Technology, 2006
    Co-Authors: T. Wakui, J. Malzbender, R.w. Steinbrech
    Abstract:

    The strain dependency of the Stiffness of bonded and free-standing thermal barrier coatings (TBCs) was analyzed using four point bending. The deformation in top and side face of the material was observed in-situ using optical and scanning electron microscopy. For freestanding TBCs, the strain of the tensile part above the neutral bending axis was larger than on the compressive part. Furthermore, the ratio of strain of tensile to compressive part increased with increasing applied strain and the position of the neutral axis sifted further to compressive side. The Stiffness for free-standing TBC changed from 8 to 17 GPa with applied strain. For bonded TBCs, the average Stiffness under tensile or compressive bending was determined considering residual stresses. The Stiffness of the bonded TBCs increased from 12 to 38 GPa as the applied strain was increased from -0.75 to 0.11%. This strong strain dependency of the TBC Stiffness can be associated with the large number of micro-cracks and pores. Finally, a unifying stress-strain curve is presented for strains from -0.75 to 0.23% obtained using results of the free-standing and bonded TBC. (c) 2005 Elsevier B.V All rights reserved

  • Strain Dependent Stiffness of plasma sprayed thermal barrier coatings
    Surface & Coatings Technology, 2005
    Co-Authors: T. Wakui, J. Malzbender, R.w. Steinbrech
    Abstract:

    Abstract The strain dependency of the Stiffness of bonded and free-standing thermal barrier coatings (TBCs) was analyzed using four point bending. The deformation in top and side face of the material was observed in-situ using optical and scanning electron microscopy. For free-standing TBCs, the strain of the tensile part above the neutral bending axis was larger than on the compressive part. Furthermore, the ratio of strain of tensile to compressive part increased with increasing applied strain and the position of the neutral axis sifted further to compressive side. The Stiffness for free-standing TBC changed from 8 to 17 GPa with applied strain. For bonded TBCs, the average Stiffness under tensile or compressive bending was determined considering residual stresses. The Stiffness of the bonded TBCs increased from 12 to 38 GPa as the applied strain was increased from − 0.75 to 0.11%. This strong strain dependency of the TBC Stiffness can be associated with the large number of micro-cracks and pores. Finally, a unifying stress–strain curve is presented for strains from − 0.75 to 0.23% obtained using results of the free-standing and bonded TBC.

  • Mechanical and thermal stresses in multilayered materials
    Journal of Applied Physics, 2004
    Co-Authors: J. Malzbender
    Abstract:

    A general solution for elastic deformation of monolithic and multilayered materials due to external loads and moments, mismatch in thermal expansion, and temperature gradients is derived. Special consideration is given to materials with stress Dependent Stiffness or gradient in elastic modulus. The relationships can be used to determine the Stiffness, thickness, thermal expansion coefficient, or thermal gradient. The fracture of a monolithic material with stress Dependent Stiffness and the temperature dependence of the elastic modulus and thickness are considered as well as the possibility to use the change in curvature in the case of delamination to determine the fracture energy.

  • determination of the stress Dependent Stiffness of plasma sprayed thermal barrier coatings using depth sensitive indentation
    Journal of Materials Research, 2003
    Co-Authors: J. Malzbender, R.w. Steinbrech
    Abstract:

    The elastic response of atmospheric plasma-sprayed coatings was investigated using Vickers and spherical indenter geometries. In both cases a strong dependency of the Stiffness on the applied load (indentation depth) was observed. The Stiffness of the coatings decreased with increasing load for a Vickers indenter, whereas it increased for a spherical indenter. This contrary behavior was related to the relative crack density in the deformed volume and to the stress dependence of the Stiffness due to crack closure. The effect of annealing on the Stiffness was quantified for both tip geometries. The heat treatment yielded additional information on the relationship between the indentation data and the microstructural defects. From the results it was concluded that the Stiffness measured using a sharp indenter and small load reflected the elastic behavior of single spraying splats. With the relatively large spherical indenter, the average global Stiffness of the thermal barrier coating was measured even at small loads. From the data obtained using the spherical indenter, a compressive stress-strain curve was suggested. Furthermore, values of the apparent crack density and yield strength were determined from the indentation tests.

R.w. Steinbrech - One of the best experts on this subject based on the ideXlab platform.

  • Strain Dependent Stiffness of plasma sprayed thermal barrier coatings
    Surface and Coatings Technology, 2006
    Co-Authors: T. Wakui, J. Malzbender, R.w. Steinbrech
    Abstract:

    The strain dependency of the Stiffness of bonded and free-standing thermal barrier coatings (TBCs) was analyzed using four point bending. The deformation in top and side face of the material was observed in-situ using optical and scanning electron microscopy. For freestanding TBCs, the strain of the tensile part above the neutral bending axis was larger than on the compressive part. Furthermore, the ratio of strain of tensile to compressive part increased with increasing applied strain and the position of the neutral axis sifted further to compressive side. The Stiffness for free-standing TBC changed from 8 to 17 GPa with applied strain. For bonded TBCs, the average Stiffness under tensile or compressive bending was determined considering residual stresses. The Stiffness of the bonded TBCs increased from 12 to 38 GPa as the applied strain was increased from -0.75 to 0.11%. This strong strain dependency of the TBC Stiffness can be associated with the large number of micro-cracks and pores. Finally, a unifying stress-strain curve is presented for strains from -0.75 to 0.23% obtained using results of the free-standing and bonded TBC. (c) 2005 Elsevier B.V All rights reserved

  • Strain Dependent Stiffness of plasma sprayed thermal barrier coatings
    Surface & Coatings Technology, 2005
    Co-Authors: T. Wakui, J. Malzbender, R.w. Steinbrech
    Abstract:

    Abstract The strain dependency of the Stiffness of bonded and free-standing thermal barrier coatings (TBCs) was analyzed using four point bending. The deformation in top and side face of the material was observed in-situ using optical and scanning electron microscopy. For free-standing TBCs, the strain of the tensile part above the neutral bending axis was larger than on the compressive part. Furthermore, the ratio of strain of tensile to compressive part increased with increasing applied strain and the position of the neutral axis sifted further to compressive side. The Stiffness for free-standing TBC changed from 8 to 17 GPa with applied strain. For bonded TBCs, the average Stiffness under tensile or compressive bending was determined considering residual stresses. The Stiffness of the bonded TBCs increased from 12 to 38 GPa as the applied strain was increased from − 0.75 to 0.11%. This strong strain dependency of the TBC Stiffness can be associated with the large number of micro-cracks and pores. Finally, a unifying stress–strain curve is presented for strains from − 0.75 to 0.23% obtained using results of the free-standing and bonded TBC.

  • determination of the stress Dependent Stiffness of plasma sprayed thermal barrier coatings using depth sensitive indentation
    Journal of Materials Research, 2003
    Co-Authors: J. Malzbender, R.w. Steinbrech
    Abstract:

    The elastic response of atmospheric plasma-sprayed coatings was investigated using Vickers and spherical indenter geometries. In both cases a strong dependency of the Stiffness on the applied load (indentation depth) was observed. The Stiffness of the coatings decreased with increasing load for a Vickers indenter, whereas it increased for a spherical indenter. This contrary behavior was related to the relative crack density in the deformed volume and to the stress dependence of the Stiffness due to crack closure. The effect of annealing on the Stiffness was quantified for both tip geometries. The heat treatment yielded additional information on the relationship between the indentation data and the microstructural defects. From the results it was concluded that the Stiffness measured using a sharp indenter and small load reflected the elastic behavior of single spraying splats. With the relatively large spherical indenter, the average global Stiffness of the thermal barrier coating was measured even at small loads. From the data obtained using the spherical indenter, a compressive stress-strain curve was suggested. Furthermore, values of the apparent crack density and yield strength were determined from the indentation tests.

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

  • a non linear inverse vibration problem of estimating the time Dependent Stiffness coefficients by conjugate gradient method
    International Journal for Numerical Methods in Engineering, 2001
    Co-Authors: Chenghung Huang
    Abstract:

    An iterative regularization method, i.e. the conjugate gradient method (CGM) is applied to an inverse non-linear force vibration problem to estimate the unknown time-Dependent Stiffness coefficients (or spring constants) in a damped system by using the measured system displacement. It is assumed that no prior information is available on the functional form of the unknown Stiffness coefficients in the present study, thus, it is classified as the function estimation in inverse calculation. The accuracy of the inverse analysis is examined by using the simulated exact and inexact displacement measurements. The numerical simulations are performed to test the validity of the present algorithm by using different types of Stiffness coefficients and measurement errors. Results show that an excellent estimation on the time-Dependent spring constants can be obtained with any arbitrary initial guesses within a couple of seconds of CPU time at Pentium III-500 MHz PC. Copyright © 2001 John Wiley & Sons, Ltd.

  • A non‐linear inverse vibration problem of estimating the time‐Dependent Stiffness coefficients by conjugate gradient method
    International Journal for Numerical Methods in Engineering, 2001
    Co-Authors: Chenghung Huang
    Abstract:

    An iterative regularization method, i.e. the conjugate gradient method (CGM) is applied to an inverse non-linear force vibration problem to estimate the unknown time-Dependent Stiffness coefficients (or spring constants) in a damped system by using the measured system displacement. It is assumed that no prior information is available on the functional form of the unknown Stiffness coefficients in the present study, thus, it is classified as the function estimation in inverse calculation. The accuracy of the inverse analysis is examined by using the simulated exact and inexact displacement measurements. The numerical simulations are performed to test the validity of the present algorithm by using different types of Stiffness coefficients and measurement errors. Results show that an excellent estimation on the time-Dependent spring constants can be obtained with any arbitrary initial guesses within a couple of seconds of CPU time at Pentium III-500 MHz PC. Copyright © 2001 John Wiley & Sons, Ltd.

Stephen D. Evans - One of the best experts on this subject based on the ideXlab platform.

  • Temperature Dependent Stiffness and visco-elastic behaviour of lipid coated microbubbles using atomic force microscopy
    Soft Matter, 2012
    Co-Authors: Colin A. Grant, J. E. Mckendry, Stephen D. Evans
    Abstract:

    The compression Stiffness of a phospholipid microbubble was determined using force-spectroscopy as a function of temperature. The Stiffness was found to decrease by approximately a factor of three from ∼0.08 N m−1, at 10 °C, down to ∼0.03 N m−1 at 37 °C. This temperature dependence indicates that the surface tension of lipid coating is the dominant contribution to the microbubble Stiffness. The time-Dependent material properties, e.g. creep, increased non-linearly with temperature, showing a factor of two increase in creep-displacement, from ∼24 nm, at 10 °C, to 50 nm, at 37 °C. The standard linear solid model was used to extract the visco-elastic parameters and their determination at different temperatures allowed the first determination of the activation energy for creep, for a microbubble, to be determined.

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

  • Strain Dependent Stiffness of plasma sprayed thermal barrier coatings
    Surface and Coatings Technology, 2006
    Co-Authors: T. Wakui, J. Malzbender, R.w. Steinbrech
    Abstract:

    The strain dependency of the Stiffness of bonded and free-standing thermal barrier coatings (TBCs) was analyzed using four point bending. The deformation in top and side face of the material was observed in-situ using optical and scanning electron microscopy. For freestanding TBCs, the strain of the tensile part above the neutral bending axis was larger than on the compressive part. Furthermore, the ratio of strain of tensile to compressive part increased with increasing applied strain and the position of the neutral axis sifted further to compressive side. The Stiffness for free-standing TBC changed from 8 to 17 GPa with applied strain. For bonded TBCs, the average Stiffness under tensile or compressive bending was determined considering residual stresses. The Stiffness of the bonded TBCs increased from 12 to 38 GPa as the applied strain was increased from -0.75 to 0.11%. This strong strain dependency of the TBC Stiffness can be associated with the large number of micro-cracks and pores. Finally, a unifying stress-strain curve is presented for strains from -0.75 to 0.23% obtained using results of the free-standing and bonded TBC. (c) 2005 Elsevier B.V All rights reserved

  • Strain Dependent Stiffness of plasma sprayed thermal barrier coatings
    Surface & Coatings Technology, 2005
    Co-Authors: T. Wakui, J. Malzbender, R.w. Steinbrech
    Abstract:

    Abstract The strain dependency of the Stiffness of bonded and free-standing thermal barrier coatings (TBCs) was analyzed using four point bending. The deformation in top and side face of the material was observed in-situ using optical and scanning electron microscopy. For free-standing TBCs, the strain of the tensile part above the neutral bending axis was larger than on the compressive part. Furthermore, the ratio of strain of tensile to compressive part increased with increasing applied strain and the position of the neutral axis sifted further to compressive side. The Stiffness for free-standing TBC changed from 8 to 17 GPa with applied strain. For bonded TBCs, the average Stiffness under tensile or compressive bending was determined considering residual stresses. The Stiffness of the bonded TBCs increased from 12 to 38 GPa as the applied strain was increased from − 0.75 to 0.11%. This strong strain dependency of the TBC Stiffness can be associated with the large number of micro-cracks and pores. Finally, a unifying stress–strain curve is presented for strains from − 0.75 to 0.23% obtained using results of the free-standing and bonded TBC.