Mechanical and Thermal Material Properties of Restraint ...

1© 2018 The Aerospace Corporation

Mechanical and Thermal Material

Properties of Restraint Filaments

for Use in Low Cost Satellites

Joseph Severino, Naoki Oishi

CubeSat Developer’s Workshop 2018

April 30 2018 – May 2, 2018

2

Outline

• Background/Motivation

• Materials Introduction-Fiber Types

• Mechanical Properties

• Thermal Cutting

– DMA (Table/Scatter Plot)

– Heating Coil (Air/Vac)

• Friction Coefficients

• CTE under Load

• Conclusion

3

Background/Motivation

• Complexity of CubeSats is expanding with new

deployable structures

– Antenna -- Booms

– Solar panels -- Others

• Lightweight and compact actuating mechanisms

necessary to fit into restrictive cube format.

– Shape memory alloy latches

– Paired CTE alloys

– Nichrome burn wires

• low mass | compact | simple

• Various configurations of burn wires

– all rely on melting a thermoplastic filament that restrains

components

• Goal here was to evaluate the materials properties of

various low cost filament materials (fishing line) used in

CubeSats to determine the advantages and

disadvantages of their application. Patented nichrome

cutting mechanism

Japanese

Waseda-SAT3

Filament

Filament

[2][3]

[1]

[1] Miyashita et al. Expansion and Measurement of Spiral Folded Membrane by Small Satellite. 55th AIAA Aerospace Sciences Meeting, Grapevine,

Texas, January 9 - 13 2017

[2] Thurn et al. A Nichrome Burn Wire Release Mechanism for CubeSats. Proceedings of the 41st Aerospace Mechanisms Symposium, Jet

Propulsion Laboratory, May 16-18, 2012

[3] US20150102172A1, Burn Wire Release Mechanism for Spacecraft and Terrestrial Applications

4

Materials

Trade Name Material Formula

MonofilamentPolyamide

(Nylon)

FluorocarbonPolyvinylidene fluoride

(PVDF)

BraidPolyethylene

(UHMWPE)

DacronPolyethylene terephthalate

PET

m

5

Mechanical Properties

Only UHMWPE has significantly different stiffness and strength within group

• Compared the 4 types of filaments

– UHMWPE far out performs rating

– PET underperforms but has low

scatter

• Compared filament rating of common

Nylon

– Properties similar but failure load

increases

– Congruent to increase in filament

diameter

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30

Lo

ad

(lb

s)

Strain (%)

UHMWPE

Nylon

PVDF

PET

Material Rating Failure Load Failure Strain DiameterLbs Lbs % mil

UHMWPE 10 32.3 ± 3.2 2.7 ± 0.4 8PVDF 10 10.7 ± 0.5 26.5 ± 2.8 11PET 12 10.2 ± 0.1 27.0 ± 0.6 15

Nylon 4 7.2 ± 0.2 24.9 ± 1.4 8Nylon 8 11.9 ± 0.9 23.7 ± 3.2 11Nylon 10 13.4 ± 0.6 24.1 ± 2.0 12Nylon 12 16.7 ± 0.5 26.1 ± 2.8 130

5

10

15

20

0 5 10 15 20 25 30

Lo

ad

(Lb

s)

Strain (%)

Nylon 12Lb

Nylon 8lb

Nylon 4lb

6

Nichrome Coiled Wire Cutting

Filaments cut instantaneously well below incandescence of nichrome wire

V

Nichrome Coil

Filament

1.1 N

Weights DC Power Supply

0

0.5

1

1.5

2

2.5

PE PVDF Nylon PET

Wat

ts

Filament Thermal Cutting

0

100

200

300

400

500

0 0.5 1 1.5 2 2.5

Tem

per

atu

re (°C

)

Watts

Thermocouple Temperature

• Investigated hot wire filament cutting in

air and vacuum

• Voltage ramped at 5 V/min until filament break

• Wattage recorded at fiber break

– Breaks were instantaneous

– Filament could consistently withstand

load when 0.01 Watts below breaking

point

• Excessive power (wire glowing red hot) was

not necessary to cut any of the filaments

– Nichrome incandescence at ~550 °C

7

Thermal Cutting

Filament breaking temperature dominated by melting point

Liquid nitrogen feed

Furnace

(open position)

Filament

-100

102030405060708090

100

25 50 75 100 125 150 175 200 225 250

Stra

in (

%)

Temperature (°C)

PETNylonUHMWPEPVDF

0.001

0.01

0.1

1

10

25 45 65

Filament DSC Melting Point (°C)

UHMWPE 156

PVDF 164

Nylon 160

PET 254

• Directly measured breaking temperature with thermal

ramp/creep test

– 5 °C/min | 4 N tension

• Breaking temperature corresponded to melting point

• Minor inflection around 40 °C

– Glass transition of Nylon 25 to 45 °C

8

Coefficient of Thermal Expansion

CTE can be negative or positive and structure changes well before melting/break

Furnace (open position)Filament

-15

-10

-5

0

5

-100 -50 0 50 100 150 200

Mic

rostr

ain

(µ

ε)

Temperature (°C)

Nylon

PET

PVDF

UHMWPE

Filament CTE (µε/°C)

UHMWPE -22.5

PVDF 30.0

Nylon 23.3

PET -7.0

• Observed thermal expansion of filaments with 0.1 N

load using TMA system

• All filaments shrunk at elevated temperature in

contrast to measurements made at 4N

– Low loads here

– Polymer softening

– Entropy

9

Coefficient of Friction

UHMWPE good for routing but nylon easier to hold without slip

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Stainless Steel Aluminum Silicone Rubber

Coe

ffic

ien

t o

f F

riction

Nylon PET PVDF UWMWPE

𝑇𝑙𝑜𝑎𝑑 = 𝑇ℎ𝑜𝑙𝑑 × 𝑒𝑥𝑝 𝜇𝜑

𝜇 = 𝐶𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑜𝑓 𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛𝜑 = 𝑎𝑛𝑔𝑙𝑒 𝑜𝑓 𝑐𝑜𝑛𝑡𝑎𝑐𝑡

Test

Arrangement

𝑇𝑙𝑜𝑎𝑑 𝑇ℎ𝑜𝑙𝑑

𝜑

• Used a capstan approach to measure sliding friction

of the fibers on 3 materials

– Stainless steel | aluminum | silicone rubber

• Consideration for complex routing or termination

approaches

10

Pinched Tensile Test

Larger diameter filaments and braids are more reliable with crush/pinch

0

5

10

15

20

25

0

100

200

300

400

500

600

700

800

900

100

0

110

0

Bre

akin

g L

oa

d, lb

f

Compressive Load, lbs

Nylon 4Lbs

0

5

10

15

20

25

0

100

200

300

400

500

600

700

800

900

100

0

110

0

Bre

akin

g L

oa

d, lb

fCompressive Load, lbs

Nylon 12Lbs

0

5

10

15

20

25

0

100

200

300

400

500

600

700

800

900

100

0

110

0

Bre

akin

g L

oa

d, lb

f

Compressive Load, lbs

PET 12Lbs

0

5

10

15

20

25

0

100

200

300

400

500

600

700

800

900

100

0

110

0

Bre

akin

g L

oa

d, lb

f

Compressive Load, lbs

UHMWPE 10Lbs

Small diameter less reliable

Braided PET has low variance

Filament rating

Filament

Average Load

Individual Load

11

Conclusions

• It is necessary to exceed the melting point of the polymer to reliably cut the

filament but it is not necessary to far exceed this temperature.

– Incandescent heating of nichrome wire unnecessary

• Cutting the filament was easier in vacuum and required less power than when

air provided convective cooling.

• UHMWPE braids appear to be the most robust filament based on strength,

cutting temperature, low friction and pinch resistance; however, unique

circumstances could make any of these filaments beneficial.

• Work still needed

– Creep

– Abrasion

– Knot retention

– Contamination and outgassing

– Space environments / radiation stability

12

Appendix

13

Fourier Transform Infrared SpectroscopyVerification of filament materials

PET

PET Match

PVDF

PVDF Match

Nylon

Nylon Match

UHMWPE

HMPE Match

14

Differential Scanning CalorimetryDetermination of Tg and Melting Point

PET

PVDFNylon

UHMWPE

15

Differential Scanning CalorimetryNylon Tg by DSC After Vacuum Drying

Nylon Tg is lower with absorbed moisture from atmosphere

Dry Tg 46°C

Nylon fiber as received

Nylon fiber vacuum dried

As received Tg 25°C