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Electromechanical instability

Electromechanical instability. Zhigang Suo Harvard University 2:00 pm – 2:45 pm, 11 January 2010, Monday PhD Winter School Dielectric Elastomer Transducers Monte Verita, Ascona, Switzerland, 11-16 January 2010 http://www.empa.ch/eap-winterschool. Theory of pull-in instability. polarizing.

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Electromechanical instability

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  1. Electromechanical instability Zhigang Suo Harvard University 2:00 pm – 2:45 pm, 11 January 2010, Monday PhD Winter School Dielectric Elastomer Transducers Monte Verita, Ascona, Switzerland, 11-16 January 2010 http://www.empa.ch/eap-winterschool

  2. Theory of pull-in instability polarizing thinning F Stark & Garton, Nature 176, 1225 (1955) Zhao, Suo, APL 91, 061921 (2007)

  3. Free energy System Dielectric Weights Battery

  4. Free energy minimized at astate of equilibrium Equations of state Critical condition for onset of instability Zhao, Suo, APL 91, 061921 (2007)

  5. Pre-stretch increases deformation of actuation Theory: Zhao, Suo APL 91, 061921 (2007) Experiment: Pelrine, Kornbluh, Pei, Joseph Science 287, 836 (2000).

  6. Cross section stiffening Coexistent states thinning polarizing F thick thin Top view Coexistent states: flat and wrinkled Observation: Plante, Dubowsky, Int. J. Solids and Structures43, 7727 (2006) Interpretation: Zhao, Hong, Suo Physical Review B 76, 134113 (2007)

  7. When stretched, a polymer stiffens n links released Langevin Gauss stretched fully stretched

  8. Stiffening due to extension limit Stiffening as each polymer chain approaches its fully stretched length (e.g., Arruda-Boyce model) m: small-strain shear modulus n: number of monomers per chain Zhao, Hong, Suo, Physical Review B 76, 134113 (2007). Zhao, Hong, Suo Physical Review B 76, 134113 (2007)

  9. FEM: inhomogeneous deformation Thin State Transition Thick State Thick State Transition Thin State Zhou, Hong, Zhao, Zhang, Suo, IJSS, 2007

  10. or + + + + + + + + + + + + + + + + + + – – – – – – – – – – – – – – – – – – stable unstable Failure Modes Rupture Loss of Tension Electrical Breakdown Electromechanical Instability

  11. Allowable states of atransducer allowable states Pei, Pelrine, Stanford, Kornbluh, Rosenthal, Meijer, Full Proc. SPIE 4698, 246 (2002) Moscardo, Zhao, Suo, Lapusta JAP 104, 093503 (2008)

  12. Energy harvesting Generate electricity from walking Generate electricity from waves Pelrine, Kornbluh…

  13. Maximal energy that can be converted by a dielectric elastomer 6 J/g, Elastomer (theory) 0.4 J/g, Elastomer (experiment) 0.01 J/g ceramics E=0 EMI R EB LT Koh, Zhao, Suo, Appl. Phys. Lett. 94, 262902 (2009)

  14. A “practical” design 2 J/g Koh, Zhao, Suo, Appl. Phys. Lett. 94, 262902 (2009)

  15. Summary • Pull-in instability: coupling large deformation and electric charge. • Pre-stretch increases actuation strain. • Co-existent states: stiffening due to extension limit. • Allowable states: as defined by various modes of failure

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