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Biaxial bulge testing of thin films and foils

Biaxial bulge testing of thin films and foils. Miroslav Cieslar Faculty of Mathematics and Physics Charles University, Prague Czech Republic. J.L. Martin, A. Karimi: EPFL Lausanne, Switzerland C. Fressengeas: LPMM, Universit é de Metz, France. Schedule.

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Biaxial bulge testing of thin films and foils

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  1. Biaxial bulge testing of thin films and foils Miroslav Cieslar Faculty of Mathematics and Physics Charles University, Prague Czech Republic J.L. Martin, A. Karimi: EPFL Lausanne, Switzerland C. Fressengeas: LPMM, Université de Metz, France

  2. Schedule • Introduction to small structure testing • Bulge test • Applications • Recrystallization of thin foils • Plastic instabilities in Al foils • Plastic deformation of thin metallic films

  3. Most common experimental methods • Films adhered to substrate • Nanoindentation (hardness, modulus) • Microbeam bending (fatigue, bending) • Wafer curvature (biaxial strain, thermal fatigue) • Free standing films • Tensile test (difficult sample preparation) • Microbeam bending • Biaxial bulge test

  4. Biaxial bulge test Industrial requirements for reliable biaxial tests Testing of membranes in micro- and nano-devices Finstocks for heat exchangers

  5. Biaxial bulge test Spherical cap model

  6. Biaxial test with a constant fluid flow-rate Stress [MPa] Time [s]

  7. Biaxial test under constant stress-rate Stress-rate [MPa/s] Time [s]

  8. Element Fe Si Cu Mn Mg Zn Ti Al wt. % 0.51 0.61 0.007 0.020 0.0066 0.022 0.024 bal. Examples • Thin Al-Fe-Si foils (thickness 8.5 mm)

  9. Initial microstructure after homogenization 590 °C/30 min

  10. Recrystallization of thin foils Stress – strain curves obtained from bulge tests during prestraining and after annealing at indicated temperatures.

  11. Yield stress variation of predeformed aluminium foils with annealing temperature

  12. Microstructure after predeformation and annealing initial 200 °C 380 °C 590 °C

  13. Plastic instabilities in Al–Fe-Si foils

  14. Instabilities after strain rate jump

  15. Instabilitiesafter an instant increase of stress by 3 MPa

  16. Portevin – Le Chatelier effect?

  17. Stress or strain oscillations?

  18. Stability analysis Constitutive equation Homogeneous solution Evolution of perturbations

  19. Stability analysis The rate of perturbations growth Instability grow w>0

  20. Stability analysis For positive SRS se~єen Hill’s criterion For negative SRS

  21. Simulations Ring-shaped zone of localized intense strain rate

  22. Simulations

  23. Thin film plastic deformation Biaxial plastic deformation of Al thin films

  24. Biaxial plastic deformation of Al thin films Influence of temperature

  25. Biaxial plastic deformation of Al thin films Creep-fatigue tests Variation of maximum strain with the number of cycles Deformation loops received during cycling

  26. Deformation processes in Al-Zn-Mg-Cu thin films 4 m thin films from AA 7075 alloy

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