2020. 06. 29

Current status of Structural Materials

Hyun Wook Na & Ji Young Kim

Self-regulating shape memory alloy robots

controlled with soft ionic skin strain sensor

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Contents

Proposal of Self-regulating SMA strain sensor

Material selection & cyclic training for two-way SME

Two-way SMA as electrode of capacitive ionic sensor

Fabrication of Capacitive ionic sensor

Adhesion of SMA and hydrogel

Demonstration of Capacitive ionic sensor operation

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Proposal of Self-regulating soft robot

Joule heating

Two-way SME(High T shape)

Strain sensing

Voltage control

Two-way SME (Low T shape)

Strain sensing

Voltage control

Scheme of self-regulating shape memory alloy robots with ionic skin

Fast and strong reversible actuation controlled by joule heating with simple system

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Motivation of developing self-regulating sensor

Limitation of Low actuation stress, Low actuation frequency

Ionic hydrogel gripper

Zheng, J., et al. (2018). "Mimosa inspired bilayer hydrogel actuator functioning in multi-environments." Journal of Materials Chemistry C 6(6): 1320-1327.

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Motivation of developing self-regulating sensor

Limitation of Complex control system for high actuation frequency and stress

Rothermund et al, Bistable valve for autonomous control of soft actuators, Science Robotics (2018) p.7986

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Motivation of developing self-regulating sensor

Motivation of this study

Temperature sensitive shape change

Rapid response to the situation (Temp.)

Structural materials

Two-way SMA

Capacitive strain sensorSandwich structure of

Electrode / Dielectric layer / ionic hydrogel

Electrode metal – ionic hydrogel layer structure

Electrode

Ionic Hydrogel

Dielectric layer

Sensitive sensing system

Skin-like soft compliance

Simple layer structure

Capacitive ionic sensor

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Two-way Shape memory alloys

Two-way SMA

https://www.youtube.com/watch?v=xhykVMFDULk

J Ma, I Karaman & R.D. Noebe, Internatinal Materials Reviews 55 (2010)

https://en.wikipedia.org/wiki/Shape-memory_alloy

Various Application as temperature sensitive sensor / grabber

Stress

Heat

Cool

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Two-way Shape memory alloys

J Ma, I Karaman & R.D. Noebe, Internatinal Materials Reviews 55 (2010)

https://en.wikipedia.org/wiki/Shape-memory_alloy

Thermally-induced martensite(Various variants, Twinned M)

Stress-induced martensite(Single variant, Detwinned M)

ㅡMacroscopic shape, size

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Material selection for Two-way SMA as Capacitive sensor

Condition : Low T (Room temperature) ↔ High T (Joule heating)

S.Y. Yang et al., Journal of Alloys and Compounds 490 (2010) L28-L32

B . Stranadel et al., Materials Science and Engineering A 202 (1995) 148-156

electric power input : 12.09 W

1.338V, 9.04A

(Resistance SMA wire : 4.933Ω/m)

“Temperature gradient from 504K to 413K

is developed by the Joule heating”

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30 40 50 60 70 80-25

-20

-15

-10

-5

0

5

10

15

20

25

Heating →

← Cooling MS = 55oCMf = 40oC

Af = 70oCAs = 57oC

← E

xoth

erm

ic (W

/g)

Temperature ( oC )

Phase transformation temperature of Ti50Ni40Cu10

DSC analysis (10K/min)

To reach the phase transformation temperature via joule heating

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Thermomechanical Cyclic training

Select A2 cyclic training method among 4 different method (100 Cycle)

Diverse cyclic training method to apply two-way SME

Y. LIU et al., Acta metall. Mater. 38 (1990) 1321-1326.

“Training is a procedure to develop dislocation arrangements

which guide the formation of martensite variants of a preferred orientation”

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Cyclic training | Two-way Shape memory effect

High T (T > Af) Low T (T < Mf)

100 cycle

w/o stress

with stress

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T > Af T < Mf

Cyclic training | Two-way Shape memory effect

After 100 cycle

1. To improve change of curvature

Thickness reduction (Cold-Rolling & Heat-treatment)

2. To improve resistance for joule heating Width reduction

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Cyclic training | Two-way Shape memory effect

We improved curvature difference by reducing the thickness of specimen.

Thickness : 1.1 mm → 0.8mm (27% cold-rolled)

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Two-way Shape memory effect via Joule heating

Heating Cooling

Movie (x4)

We confirmed the two-way shape memory effect via joule heating.

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When uniaxial force stretches dielectric 𝝀𝝀 times,

both the width and the thickness of the dielectric reduce by a factor of 𝝀𝝀,

and the capacitance of the dielectric scales as 𝑪𝑪 = 𝑪𝑪𝟎𝟎𝝀𝝀

Fabrication of Capacitive ionic sensor

Shape Memory Alloy

Ionic hydrogelDielectric layer (3M VHB)

= Rigid Backbone + Electrode + Fast actuator

= Soft cover + Sensor

V

1𝐶𝐶 =

2𝐶𝐶𝐸𝐸𝐸𝐸𝐸𝐸

+1𝐶𝐶𝐸𝐸

𝐶𝐶𝐸𝐸𝐸𝐸𝐸𝐸/𝐶𝐶 ≈ 105

∴ 𝐶𝐶 ≈ 𝐶𝐶𝐸𝐸

V

Ad 𝐶𝐶 =

𝜖𝜖0𝐴𝐴𝑑𝑑

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Adhesion of SMA and hydrogel

Yuk, H., et al. (2016). "Tough bonding of hydrogels to diverse non-porous surfaces." Nat Mater 15(2): 190-196.

Tough bonding between shape memory alloy and hydrogel was achieved by silane coupling reaction

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Demonstration of Capacitive ionic sensor operation

(Normal) (Pressed)

20222426283032343638

0 10 20 30 40 50

Capa

cita

nce(

pF)

Time(s)

Capacitive ionic sensor with SMA successfully operated by finger pressure

V

Ad 𝐶𝐶 =

𝜖𝜖0𝐴𝐴𝑑𝑑

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Demonstration of Capacitive ionic sensor operation

1.6

1.65

1.7

1.75

1.8

1.85

0 10 20 30 40 50

Capa

cita

nce(

nF)

Time(s)

Heating

1.95

2

2.05

2.1

2.15

2.2

2.25

2.3

0 20 40 60 80 100 120 140

Capa

citn

ace(

nF)

Time(s)

Cooling

Confirm capacitance change, however very small signal-to-noise ratio, and capacitance changes by contact surface

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Summary

Scheme of proposed self-regulating shape memory alloy robots with ionic skin

Joule heating

Two-way SME (High T

shape)

Strain sensing

Voltage control

Two-way SME (Low T shape)

Strain sensing

Voltage control

Significance of this study

Sensitive sensing system

Skin-like soft compliance

Simple layer structure

Temperature sensitive shape change

Rapid response to the situation (Temp.)

Structural materials

Two-way SMA Capacitive ionic sensor

Fast and strong reversible actuation controlled by joule heating with simple system

Thank you for your kind attention

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Supplementary

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Supplementary

Beams: Pure Bending (4.1-4.5) MAE 314 – Solid Mechanics Yun Jing Beams: Pure Bending.

Thickness : 0.8mm 기준으로,

Diameter = 2cm → 4% Compressive / tensile strain

Diameter = 2.5cm → 3.2% Compressive / tensile strain

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Supplementary

A1, B1, B2 → High permanent strain

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Yuk, H., et al. (2017). "Hydraulic hydrogelactuators and robots optically and sonicallycamouflaged in water." Nat Commun 8: 14230.stresses. We further demonstrate that the

agile and transparent hydrogel actuators and robots perform extraordinary functionsincluding swimming, kicking rubber-balls and