WilliamLAI - From Rigid to Soft

Characterization, Analysis and
Fabrications of Soft Dielectric
Elastomer Actuators Capable of
Complex 3D Deformation
Presenter: William Lai
Department of Aerospace Engineering, Engineering Mechanics
Iowa State University

Outline
• Motivation
• Literature Review
• Actuator Design and Fabrication
• Actuator Analysis
• Effect of Surface Reinforcements and Their Applications
• Summary

Motivation
• Learn from Nature: From rigid to soft
• Soft flexible Actuators: arms, grippers, flappers…etc.
• Higher flexibility and degree of freedom: able to adapt
complicated and unpredictable environment
Motivation Literature Review Actuator Design and Fabrication Actuator Analysis Effect of Surface Reinforcements Surface Reinforcement Applications

• Flexible structures:
Complaint material with designed structural patterns
Actuated through strings, air pressure, or others
Soft Actuator Development: Structure
R. F. Shepherd et al., National Academy of Sciences of USA, 2011.
B Mazzolai et al., Bioinsp. Biomim. 7, 2012
M Calisti, M Giorelli et al.,
Bioinsp. Biomim. 6, 2011

• Active materials:
Shape memory alloy, Piezoelectric ceramic…etc.
• Soft Active polymers:
(thermo-, magnetic-, pH-, photo-, electro-active
polymers)…etc.
Soft Actuator Development: Material

• Able to deform through electrical stimulation
• Caused by ion migration or electrostatic forces
conductive polymer
electrolyte
V
ex. Conductive polymers ex. Dielectric elastomers (DEs)
Ionic EAPs Electronic EAPs
Electroactive Polymers (EAPs)
Low voltage required (< 10V)
Slow reaction (above 10 sec.)
High voltage required (103 V)
(Low current, low power)
Fast response time (sec.)

Dielectric Elastomers
• Why dielectric elastomers?
– Soft, light, and flexible
– Large deformation range
– Low cost and easy availability
• Actuation mechanism
– Compliant elastomer sandwiched by compliant electrodes
– Driven by Maxwell stress :
V
σMaxwell
𝜎𝜎𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 = 𝜖𝜖𝜖𝜖0Φ2
σMaxwell
elastomer
electrode

Actuator Design in Literatures
• Requires of prestretch*  additional hard frame for supporting
• In-plane motion, in-frame motion
• Lower energy to mass ratio. Lower actuation degree of freedom
A. Wingert et al., IEEE/ASME
Transactions on Mech., 2006S. Dastoor et al., IEEE ICRA 2012
I. A. Anderson et al.,
Appl. Phy. A, 2010.
In-plane rotator:
Variable stiffness device:
Axial extensor:

Research Goal
• Develop free-standing flexible actuator
– Provide higher DoF motion with lighter weight
• Actualize actuator design
• Characterize materials and actuator
– Study deformation mechanism
• Increase actuator performance and control force-
stroke characteristics

• From: bi-material thermostat
• To: active + inactive membrane stacks
Actuator Concept
Active layer
Inactive layer
Actuation

Procedure and Design
• Planar actuator (active layer)
• Stack with Stiffeners (inactive layer)
Actuator Design and Fabrication
2 cells
N cells…3 cells
1 cell
Building blockElectrode
elastomer
elastomer
Electrode terminals (Aluminum foil)
Stiffener
Sealing region
Electrode
Dielectric elastomer:
3M VHB F9460PC
(50µm thick)
Compliant electrode:
carbon black particles
Stiffener:
3M Scotch tapes
(65µm thick)
25mm

Actuator Performance and Analysis

Device Performance
Deformation sequence of 1, 2,
3-cell actuators
2 cells
3 cells
1 cell

Measured curvature of
1, 2, 3-cell actuators
0
0.02
0.04
0.06
15000 17500 20000 22500
κ(1/mm)
Φ0 (V/mm)
Experiment 1c-1s
Experiment 2c-1s
Experiment 3c-1s
1-cell
2-cell
3-cell
Curvature increases

Analytical Model
Timoshenko bi-material laminate solution
Layer 1 (stiffener)
Layer 2 (EAP)
𝑎𝑎1
𝑎𝑎2
Layer 1
Layer 2
𝑀𝑀1
𝑀𝑀2
𝑃𝑃1
𝑃𝑃2
or electrical
total thermal axial bendingε ε ε ε= + +
1 1 1 2 2 2
1 1 1 2 2 2
1 2
1 1 1 1
2 2
thermal thermal
or electrical or electrical
w P a w P a
E a w E a w
ε ε
ρ ρ
+ + = − −
At the interface of layer 1 and 2
𝑤𝑤1
𝑤𝑤2

Analytical Model
1
1
1
2 2
2
M
M
E I
E I
ρ
ρ
=
=
1 1 2 2
1
1 2
1 2 2
2
2
h
P M M
w P w P P
P
I
h
E E I
ρ ρ
=
=
=
+
=
+
=
Layer 1 (stiffener)
Layer 2 (EAP)
𝑎𝑎1
𝑎𝑎2
Layer 1
Layer 2
𝑀𝑀1
𝑀𝑀2
𝑃𝑃1
𝑃𝑃2
1 2h a a= +
𝑤𝑤1
𝑤𝑤2
2
0 0
2 20
0 0 0 0
1
( ) ( )
2
zz
electrical xx
E E
σ
ε ε ν
=− Φ
 Φ = = − − Φ = Φ 



0( )electricalε Φ

• Perform tensile tests on elastomers
• Assume isotropic incompressible
material with elastic behavior
Material Mechanical Property
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
3M VHB9460PC Tape
Strain
Stress(MPa)
Strain
Stress(MPa)
Tensile test of 3M VHB F9490PC Tapes
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
0
5
10
15
20
25
30
35
40
3M Magic Scotch Tape
Strain
Stress(MPa)
Strain
Stress(MPa)
Tensile test of 3M Scotch Tapes (stiffeners)
Load cell
Displacement
transducer Testing sample

Comparison of Experimental
Measurements and Model Predictions
0 0.5 1 1.5 2 2.5
x 10
4
0
0.01
0.02
0.03
0.04
0.05
0.06
Nominal E-Field (kV/mm)
Curvature(1/mm)
-- Analytical 1-cell
□ Experiment 1-cell
( )
0
0
1 1 2 2
1 1 1 2 2 2
( )
( )
2 1 1
2
electrical
h
E I E I
h E a w E a w
ε
κ
ζ β Φ
Φ =
 
+ + + 
 
β: geometric factor (accounts for
inactive layers)
ζ: fitting parameter = 0.55

• Utilizing ABAQUS with User Material (UMAT) subroutine
• Incompressible Neo-Hookean model for elastomer
• Coupling electric and mechanical fields
Finite Element Analysis
( ) ( )2 2 2 2 2 2 2
1 2 0 1 2 1 2 0 0 1 2
1 1
( , , ) 3
2 2
W λ λ µ λ λ λ λ λ λ− − − −
Φ= + + − + Φ
Shear modulus =0.033MPa Dielectric constant = 3.21**
Elastic energy Electrostatic energy
**M. Aschwanden, R. Friedlos and A. Stemmer, LEOS 2007
*X. Zhao, W. Hong, and Z. Suo, PHYSICAL REVIEW B, 2007
*
Total energy

Revealing Boundary Effect Around
Stiffener

Surface Displacement Analysis
Utilizing Digital Image Correlation technique, observed localized deformation
0.1
0.075
0.05
0.025
0
-0.025
-0.05
-0.075
-0.1
Logarithm Strain, Exx 0.1
0.05
0
-0.05
-0.1
-0.15
-0.2
-0.25
-0.3
Logarithm Strain, Exy
0.2
0.16
0.12
0.08
0.04
0
-0.04
-0.08
-0.12
Logarithm Strain, Eyy

Effective Width
Layer 1 (stiffener)
Layer 2 (EAP)
𝑎𝑎1
𝑎𝑎2
Layer 1
Layer 2
𝑀𝑀1
𝑀𝑀2
𝑃𝑃1
𝑃𝑃2
𝑤𝑤1
𝑤𝑤2
𝑤𝑤1= 𝑤𝑤2
0( )electricalζβε Φ

Effective Width
Layer 1 (stiffener)
Layer 2 (EAP)
𝑎𝑎1
𝑎𝑎2
Layer 1
Layer 2
𝑀𝑀1
𝑀𝑀2
𝑃𝑃1
𝑃𝑃2
𝑤𝑤1
𝑤𝑤2
𝑤𝑤1≠ 𝑤𝑤2

Effective Width
Layer 1 (stiffener)
Layer 2 (EAP)
𝑎𝑎1
𝑎𝑎2
Layer 1
Layer 2
𝑀𝑀1
𝑀𝑀2
𝑃𝑃1
𝑃𝑃2
weffw2
weff
𝑤𝑤1
𝑤𝑤2
𝑤𝑤1≠ 𝑤𝑤2

Wstiffener
Wsealing
WLocalization
eff stiffener sealing localiztionw w w w= + +
Effective Width
Motivation Literature Review Actuator Design and Fabrication Actuator Analysis Role of Stiffener Surface Stiffener Applications

• Evaluated actuator performance
• Studied deformation mechanisms
• Developed analytical model and finite element
framework, revealed localized deformation
• Localized deformation around the stiffener boundary
dominates the actuation
Summary for Actuator Analysis

• Split single stiffener into narrower segments while
keeping total bending stiffness (width) as constant
• Change the efficacy in converting axial constraints to
curvature
• Effectively use the total strain provided by the same
energy input
Role of Stiffener: Application

Deformation sequence of 3-cell actuators
with 1 & 3-segment of stiffeners
3-segment
1-segment
(kV/mm)
Fixing total width
(as well as I ) of stiffeners

Fitting Analytical Model with Experiment
( )2 2eff stiffener sealing localiztionw w w n w= + +
0 0.5 1 1.5 2 2.5
x 10
4
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
Nominal E-Field (V/mm)
Curvature(1/mm)
1 stiffener (analytical)
3 stiffeners (analytical)
1 stiffener (Experiment)
3 stiffeners (Experiment)
Wstiffener
Wsealing
WLocalization
n = amount of stiffeners

Elastic Energy in FEA
(effect of splitting stiffeners)
0
0.01
0.02
0.03
0.04
0.05
0 5000 10000 15000 20000 25000
3c-1s
3c-2s
3c-3s
3c-4s
3c-5s
Nominal E-field (V/mm)
ElasticEnergy(mJ)
3-cell-1-segment
3-cell-2-segment
3-cell-3-segment
3-cell-4-segment
3-cell-5-segment
Elastic strain energy did NOT change with stiffener splitting

3-cell-1-segment 3-cell-3-segment 3-cell-5-segment
(FEA results of half sample actuators)
Increase actuator efficacy!
Cross-sectional view of different mode of deformation

Controllable force-stroke characteristics
(effect of splitting stiffeners)
(Φ0 = 20800 V/mm)
Planar Actuator
In FEM:
Roller B.C. for reaction
force calculation

Fiber Stiffener
• Splitting stiffeners into finer segments
 Fiber electrode/ Fiber stiffeners
• Theoretically maximize efficacy, force-stroke characteristic
• Adjust actuator stiffness and electromechanical response
Motivation Literature Review Actuator Design and Fabrication Actuator Analysis Role of Stiffeners Surface Stiffener Applications

1 inch
B.) Carbon Fiber + carbon black
A.) Carbon black only
@ 8kV
Actuate
a.) b.)
Unidirectional fiber electrode on
dielectric elastomer actuators

Bat-wing inspired
woven fiber stiffeners
Supporting frame
Prestretched VHB membrane
Woven cotton fibers
Laterally prestretched
Vertically prestretched
Orthogonal
Bat wings

Structure modulus increasing
(Mechanical tensile tests)
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
0
0.5
1
1.5
2
2.5
Stretch
Stress(MPa)
0 0.2 0.4 0.6 0.8 1
0
0.2
0.4
0.6
0.8
1
Strain
Stress(MPa)
Test 60
Test 55
Test 56
Test 63
Orthogonal
Reference
No fiber

Predictable modulus of fiber-elastomer
membrane
Employing composite laminate theory
Stacking unidirectional fiber plies with elastomer matrix
Fiber orientation
𝜃𝜃1
𝜃𝜃2
𝜃𝜃3
𝜃𝜃4
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
0
0.5
1
1.5
2
2.5
Stretch
Stress(MPa)
Laterally
prestretched
Vertically
prestretched
Orthogonal
10°/170°/170°/10°
45°/-45°/-45°/45°
80°/100°/100°/80°
(𝜃𝜃1 / 𝜃𝜃2 / 𝜃𝜃3 / 𝜃𝜃4)Fiber configuration
0.127MPa
6MPa
1.2GPa
5GPa

Electromechanical actuation performance
Stretch
Voltage
Orthogonal
Reference
Trade-off between stiffness and deformability
Same material:
• Controllable for different
working condition
• Combine and apply in
different applications

Summary
• Accomplishment of prototype actuator fabrication: freestanding 2D
planar actuator, capable of complex 3D motion, with no prestretch
requirement.
• Developed analytical and finite element modeling framework,
providing amenable models for control strategies.
• Studied role of stiffener on bender actuators. Utilized findings to
improve actuator performance and control actuator characteristics
• Expanded study on fiber: patterned woven fibers with marked effects
on actuator mechanical properties and electromechanical response.
Same material adjustable for a variety of applications.

Publications and Conference Presentations
Publications
• W. Lai, A. Bastawros, and W. Hong, “Effect of bat-wing inspired surface reinforcements on soft dielectric elastomer
actuators,” Prospective Publication (proceeding)
• W. Lai, A. Bastawros, W. Hong, “Distributed surface stiffener on free standing dielectric elastomer actuators with over 100%
improved performance,” Prospective Publication in Journal of Applied Mechanics (proceeding)
• W. Lai, A. Bastawros, W. Hong, and S.-J Chung, “Performance of planar dielectric elastomer actuator with stiffeners for large
rotational actuation,” Prospective Publication in Smart Materials and Structures (Submitted)
• W. Lai, A. Bastawros, H. Wang, A. Antoniou, “Application of Digital Image Correlation for Multiscale Biomechanics,”
Handbook of Imaging in Biological Mechanics, chapter 11, CRC Press, 2014
• W. Lai, A. Bastawros, W. Hong, and S.-J Chung, “Fabrication and Analysis of Planar Dielectric Elastomer Actuators Capable of
Complex 3-D Deformation,” 2012 IEEE International Conference on Robotics and Automation, May 6, 2012, Minneapolis, MN
• W. Lai, A. Bastawros, and W. Hong, “Complex 3D Motion of a Planner Dielectric Elastomer Actuator with Distributed
stiffeners.” SPIE Smart Structures/NDE Conference,” March 11, 2012, San Diego, CA
Conferences
• W. Lai, A. Bastawros, and W. Hong, “Effect of Surface Fiber Reinforcements on Dielectric Elastomer Actuators,” Science and
Engineering Society Annual Meeting, Oct 1, 2014, West Lafayette, IN
• W. Lai, A. Bastawros, W. Hong, and S.-J Chung, “Fabrication and Analysis of Planar Dielectric Elastomer Actuators Capable of
Complex 3-D Deformation,” IEEE International Conference on Robotics and Automation, May 6, 2012, Minneapolis, MN
• W. Lai, A. Bastawros, and W. Hong, “Complex 3D Motion of a Planner Dielectric Elastomer Actuator with Distributed
stiffeners,” SPIE Smart Structures/NDE Conference,” March 11, 2012, San Diego, CA
• W. Lai, A. Bastawros, and W. Hong, “Nonlinear Characteristics of Dielectric Elastomers Actuators with Biaxial Prestretch ,”
ASME Applied Mech. Mat. Conference, May 30, 2011, Chicago, IL

Thank you!
Bend & Twist!
Saddle shape!

WilliamLAI - From Rigid to Soft

WilliamLAI - From Rigid to Soft

Recommended

Recommended

More Related Content

What's hot

What's hot (19)

Similar to WilliamLAI - From Rigid to Soft

Similar to WilliamLAI - From Rigid to Soft (20)

WilliamLAI - From Rigid to Soft