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Modelling
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TUD Division of Solid Mechanics | ACMFMS 2012 |
Modelling and Simulation of Electroactive Materials and Structures
D. Gross1, B.X. Xu2, R. Müller3
1 Division of Solid Mechanics, TU Darmstadt 2 Dept. of Material Science, TU Darmstadt 3 Chair of Mechanics, TU Kaiserslautern
TUD Division of Solid Mechanics | ACMFMS 2012 |
Hillenbrand & Sessler, 2000
Ferroelectrics Ferroelectrics
Dielectric Dielectric Elastomers Elastomers
FerroelectretFerroelectrets s
+
-
P0E
E
TUD Division of Solid Mechanics | ACMFMS 2012 |
FerroelectricsFerroelectrics
electro-mechanical coupling principle
BaTiO3, PZT
T>TCurie: cubic
+
-
P0
T<TCurie: tetragonal
piezoelectric effectE<Ecoerc
polarization switchE>Ecoerc
remanent polarization, remanent strain
switching due to electrical and mechanical loads
+
-
P0
+
-
E
TUD Division of Solid Mechanics | ACMFMS 2012 |
micro structural aspectsmicro structural aspectsdomains polycrystal
Schmitt & Kleebe, 2006 Jaffe, 2001
macroscopic behaviourmacroscopic behaviour
Boehle, 1999
dielectric hystersis butterfly hystersis
damaged domains
-4 -3 -2 -1 0 1 2 3 4
-1
0
1
2
Str
ain
, s
[10
-3]
Electric Field, E [kV/mm]
TUD Division of Solid Mechanics | ACMFMS 2012 |
Lupascu, 2002
electric fatigue under cyclic loading
point defects (oxygen vacancies?)
agglomeration, interaction with domain walls
cracking
Utschig, 2005
ProblemsProblems
Deluca, 2010
TUD Division of Solid Mechanics | ACMFMS 2012 |
Basic equations
Balance laws
Constitutive relations
Kinematics and electric potential
: remanent polarization
: remanent strain
: elasticity tensor
: piezoelectric tensor
: dielectric tensor
Phase field model
TUD Division of Solid Mechanics | AK 2012 |
Phase field model
remanent polarization P is considered as order parameter
extended electric enthalpy
: local (classical) electric enthalpy
: domain separation energy
: interface energy
evolution of P (Ginzburg-Landau)
TUD Division of Solid Mechanics | AK 2012 |
interface energy
separation energy
local (classical) electric enthalpy
Numerical implementation
FEM, arbitrary geometry & boundary conditions
nodal degrees of freedom:
implicit time integration of Ginzburg-Landau equation
nonlinearity: Newton iteration required
damping and stiffness matrix required
symmetric system matrix
direct computation of configurational forces
TUD Division of Solid Mechanics | ACMFMS 2012 |
TUD Division of Solid Mechanics | ACMFMS 2012 |
Example: microstructure evolution at a crack tip
Microstructure at stationary crack tip
TUD Division of Solid Mechanics | ACMFMS 2012 |
J integral and configurational forces
TUD Division of Solid Mechanics | ACMFMS 2012 |
configurational forces
TUD Division of Solid Mechanics | ACMFMS 2012 |
Dependence on applied electric field
positive electric field inhibits crack initiation
negative electric field promotes crack initiation
Wang & Singh 1997
TUD Division of Solid Mechanics | ACMFMS 2012 |
Crack face boundary conditions
permeable:
impermeable:
semipermeable:
energy consistent:
TUD Division of Solid Mechanics | ACMFMS 2012 |
Influence of boundary conditions
TUD Division of Solid Mechanics | ACMFMS 2012 |
Open questions
influence of 2d/3d character
boundary conditions for order parameter (polarization)
conditions at grain boundaries in poly-crystals
initial conditions (virgin state of the material)
origin of the characteristic spacing of domains
importance of surrounding fields
motion of point defects in the „phase field continuum“
TUD Division of Solid Mechanics | ACMFMS 2012 |
TUD Division of Solid Mechanics | Dresden 2011 |
piezo actuators vs. dielectric elastomer actuators
piezo actuator soft actuator
coupling through constituive laws
small displacements
large actuation force
coupling through electrostatic volume forces: MAXWELL stresses
large displacements
small actuation force
Dielectric Elastomer ActuatorsDielectric Elastomer Actuators
TUD Division of Solid Mechanics | ACMFMS 2012 |
Balance laws
Constitutive relations (actual configuration)
Kinematics and electric potential
Basic equations
MAXWELL stress
Neo Hooke
TUD Division of Solid Mechanics | Dresden 2011 |
Analysis of electro-mechanical stability
initial dimension:
deformed dimension:
TUD Division of Solid Mechanics | Dresden 2011 |
Constitutive equations
Equilibrium
TUD Division of Solid Mechanics | Dresden 2011 |
Equilibrium configuration
Stability (Lagrange multiplyer strategy)
TUD Division of Solid Mechanics | Dresden 2011 |
Neo-Hooke model
special case:
Zhao & Suo, 2007
Numerics
FEM, arbitrary geometry & boundary conditions
perfect agreement between analytical and numerical results
simulation and optimization of composites possible
direct computation of configurational forces possible
simulation of dynamic response
TUD Division of Solid Mechanics | ACMFMS 2012 |
TUD Division of Solid Mechanics | ACMFMS 2012 |
homogeneous
inhomogeneous
barium titanate particle
TUD Division of Solid Mechanics | ACMFMS 2012 |
Charge Density Evolution of FerroelectretsCharge Density Evolution of Ferroelectrets
piezoelectric 2 phase material (composite)
specific interface properties
(macroscopic) coupling through constitutive law
(microscopic) coupling through electrostatic volume forces: MAXWELL stresses
large displacements
diel 2
diel 1
interface
TUD Division of Solid Mechanics | ACMFMS 2012 |
Basic equations
no breakdown: 2 dielectric materials
charge density, 1st breakdown
breakdown criterion
backfield evolution
charge density evolution
Numerics incremental time integration of internal variables
similar to plasticity with kinematic hardening
nonlinear FEM implementation
specific (embedded) interface element
TUD Division of Solid Mechanics | ACMFMS 2012 |
ePTFE FEP
Example: FEP – ePTFE unit
TUD Division of Solid Mechanics | ACMFMS 2012 |
TUD Division of Solid Mechanics | ACMFMS 2012 |
B
B
C
C
TUD Division of Solid Mechanics | ACMFMS 2012 |
ConclusionsConclusions
modeling & simulation offers a deeper insight in coupled problems
allows to replace (some) experiments
allows to analyze and optimize structures
nonlinear FEM and use of configurational forces often advantageous
TUD Division of Solid Mechanics | AK 2012 |
interface energy
separation energy
TUD Division of Solid Mechanics | ACMFMS 2012 |
Configurational forces
configurational force balance
Eshelby stress tensor, config body force
inhomogeneities (singularities) cause configurational forces
resultant configurational force:
configurational force on a point defect:
configuartional traction acting on an interface:
driving force at a domain wall:
overall driving force:
Microstrucure evolution, Poling
phase 1 : from random distribution towards equilibrium
phase 2 : application of an external field
TUD Division of Solid Mechanics | AK 2012 |
TUD Division of Solid Mechanics | ACMFMS 2012 |
3D microstructure evolution
potential free b.c.
TUD Division of Solid Mechanics | AK 2012 |
3D electric poling
TUD Division of Solid Mechanics | AK 2012 |
Influence of domain wall energy
TUD Division of Solid Mechanics | AK 2012 |
Domain wall thickness
ϵ = 8.0 e-7 m
TUD Division of Solid Mechanics | AK 2012 |
Domain wall thickness
ϵ = 5.0 e-7 m
TUD Division of Solid Mechanics | AK 2012 |
Domain wall thickness
ϵ = 2.0 e-7 m
TUD Division of Solid Mechanics | AK 2012 |
Size effect: thin films
Robin b.c.
Electric b.c.