Analysis of PVC Foam and Carbon Nanofiber Syntactic Foam

Dr. Nikhil GuptaRonald PovedaDzung Luong

Jozef PistekGreg SciameJuly/August 2010Science and Mechatronics Aided Research for TeachersSponsored by the National Science Foundation

Objective• Study, analyze and compare:▫ PVC foams▫ Syntactic foams with 1% Carbon nanofiber

• Test all materials using both static and dynamic tests

• Compare the yield strength, plateau strength, and elastic modulus across each foam type and experiment type.

• To convey test methods, instrumentations, and protocols for analysis

Testing and Comparing Two Foam Types

PVC Foam 1% CNF Syntactic Foam

PVC Foam• Lightweight• Chemically-resistant; easy to

clean• Does not absorb water• Can be stapled and screwed

into; ideal for marine upholstery and structural applications

• Forms, cuts and glues easily • Excellent insulator• Weathers well

Syntactic Foam

• Porous composite materials• Hollow glass microballoons

mixed with a hardening agent

• High elastic modulus, strength, and energy absorption

• Low moisture absorption• Strength, lightweight, and

energy absorption lead syntactic foams to applications in aerospace and marine vehicles

1% Carbon Nanofiber Syntactic Foam

• For this study, carbon nanofibers (CNF) were added to the syntactic foam mixture during production

• CNFs have high strength and modulus• This study will analyze whether the addition of

CNFs will improve the strength of syntactic foams

Specimen Preparation

Test Specimens

PVC FoamCarbon Nanofiber Syntactic Foam

10mm

5mm

Strain and Strain Rate

• Strain is defined as the ratio of change in the length of a mechanical test sample

• Strain rate (/s)is defined as the rate of change of strain with respect to time, t.

hh∆

=εhΔh

Modulus of Elasticity• The ratio of stress to strain (the measure of

resistance to elastic deformation).• Stress is a measure of the average force per

unit area.• E = Elastic Modulus = stress / strain• Units: ▫ Elastic Modulus (Pa) ▫ σ: Stress (Pa) ▫ ϵ: Strain (mm / mm)

ϵ

σ

0

1

2

3

4

5

6

7

0 0.05 0.1 0.15 0.2

Str

ess

(M

Pa

)

Strain (mm/mm)

Yield Strength• The stress at which material strain changes from

elastic deformation to plastic deformation, causing it to deform permanently.

Plateau Strength

Elastic (Recoverable) Region Plastic Region

Yield Strength

Quasi-Static Compression Testing

PVC Foam Quasi-Static Comparison

0

1

2

3

4

5

6

7

8

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

Str

ess

(MP

a)

Strain (mm/mm)

HP 250

HP 200

HP 100

HP 60

CNF Syntactic Foam Quasi-Static Comparison

0

20

40

60

80

100

120

140

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

Str

ess

(MP

a)

Strain (mm/mm)

CNF 220-30CNF 220-50CNF 460-30CNF 460-50CNF EpoxyEpoxy (Neat)

220-50

CNF Epoxy

Epoxy (Neat)

220-30

460-50

460-30

The split-Hopkinson Pressure Bar (SHPB) apparatus used in high strain rate testing of materials.

SHPB capable of testing materials in high stress at extremely higher strain rates• The split-Hopkinson

pressure bar is capable of achieving the highest uniform uniaxial stress loading of a specimen in compression at nominally constant strain rates of the order of 10³ /s

Split Hopkinson Pressure Bar Setup and Data Acquisition

High Speed Image Acquisition System

Strain Gauge

Strain Gauge

Gauge Factor:

• ΔR is the change in resistance due to strain.

• RG is the resistance of the undeformed gauge.

• ϵ is strain.

• BV is the bridge excitation voltage.

GF =ΔR/RGϵ v =

BV · GF · ϵ4

Wheatstone Bridge

Output (v) from the bridge:

Amplifier Oscilloscope

0

2

4

6

8

10

12

14

0 0.05 0.1 0.15 0.2

Str

ess

(M

Pa

)

Strain (mm/mm)

2232 /s

2288 /s

2415 /s

2488 /s

SHPB Dynamic PVC Foam ComparisonHigh Strain Rate, Varying PVC Foam Densities

HP 100 PVC Foam at Varying Strain Rates

HP 250

HP 200

HP 100

HP 60

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.05 0.1 0.15 0.2

Strain (mm/mm)

2415 /s

1897 /s

880 /s

Str

ess

(M

Pa

)

SHPB Dynamic CNF Foam Comparison

High Strain Rate, Varying CNF Foam

CNF460-30 Foam at Varying Strain Rates

0

50

100

150

200

250

0 0.05 0.1 0.15

Str

ess

(M

Pa

)

Strain (mm/mm)

1194 /s1336 /s847 /s739 /s876 /s803 /s

460-30

220-50

1% CNF

Epoxy (Neat)

220-30

460-50

0

50

100

150

200

250

0 0.05 0.1 0.15

Strain (mm/mm)

677 /s

818 /s

1047 /s

Str

ess

(M

Pa

)

-6

-5

-4

-3

-2

-1

0

1

2

3

4

600 1100 1600 2100

Str

ain

(x

10

-3

mm

/mm

)

Time (μs)

incident transmitted

HP 250, 400 psi, strain rate: 2184 /s

HP 100, 400 psi, strain rate: 2415 /s

HP 200 PVC Foam(6269 fps)

(400 psi)

(250 psi)

(100 psi)

HP 200 vs. HP 60 PVC Foam250 pounds per square inch6269 frames per second

HP 200

HP 60

HP 200 vs. HP 60 PVC Foam400 pounds per square inch6269 frames per second

HP 200

HP 60

Yield Strength/Density (MPa/kg/m³)

0.00

0.05

0.10

0.15

0.20

0.25

Static

0.00

0.05

0.10

0.15

0.20

0.25

Dynamic

Plateau Strength/Density (MPa/kg/m³)

0.00

0.05

0.10

0.15

0.20

0.25

Static

0.00

0.05

0.10

0.15

0.20

0.25

Dynamic

* * *

Elastic Modulus (MPa)

0

500

1000

1500

2000

2500

3000

3500

Static

0

500

1000

1500

2000

2500

3000

3500Dynamic

Elastic Modulus/Density (MPa/kg/m³)

0.000.501.001.502.002.503.003.504.004.50

Static

0.000.501.001.502.002.503.003.504.004.50

Dynamic

Results• For Static Testing:▫ Specific Yield Strength (CNF 460-50)▫ Specific Plateau Strength (Epoxy-neat)▫ Specific and Absolute Elastic Modulus (CNF 460-

30)• Every value tested increased with density for

PVC Foams• Trend:▫ In all static tests, PVC foam was predictable in

every category

Results• For Dynamic Testing:▫ Specific Yield Strength (CNF 460-50)▫ Specific Plateau* Strength (CNF 460-50)▫ Elastic Modulus (E) specific E: HP-60 absolute E: CNF 460-30

For Both Static and Dynamic Tests:

• Specific Yield Strength:▫ CNF 220-30 higher than CNF 220-50▫ CNF 460-50 higher than CNF 460-30

• Specific Elastic Modulus:▫ CNF 220-50 higher than CNF 220-30 ▫ CNF 460-30 higher than CNF 460-50

• PVC Foam predictable in every category except for specific modulus during dynamic SHPB tests

Yield Strength/Density (MPa/kg/m³)

0.00

0.05

0.10

0.15

0.20

0.25

Static

0.00

0.05

0.10

0.15

0.20

0.25

Dynamic

Elastic Modulus/Density (MPa/kg/m³)

0.000.501.001.502.002.503.003.504.004.50

Static

0.000.501.001.502.002.503.003.504.004.50

Dynamic

Improvements

• Tensile testing is recommended to gain a more complete understanding of the physical properties of PVC and CNF Syntactic Foams

• Repeat compression tests using more specimens per foam type

• Learning curve a factor in possible flaws in initial data acquisition

Acknowledgements • This research is supported by the Research

Experience for Teachers Site Program of NationalScience Foundation under grant EEC-0807286:Science and Mechatronics Aided Research forTeachers (SMART).

• Thank you for your support:• Professor Vikram Kapila• Dr. Nikhil Gupta• Ronald Poveda• Dzung Luong• Vasanth Shunmugasamy• Other lab personnel of Mechanical Engineering

Department of NYU-Poly

Analysis of PVC Foam and Carbon Nanofiber Syntactic FoamObjectiveTesting and Comparing Two Foam TypesPVC FoamSyntactic Foam1% Carbon Nanofiber Syntactic FoamSpecimen PreparationTest SpecimensStrain and Strain RateModulus of Elasticity �Yield StrengthQuasi-Static Compression TestingPVC Foam Quasi-Static ComparisonCNF Syntactic Foam Quasi-Static ComparisonThe split-Hopkinson Pressure Bar (SHPB) apparatus used in high strain rate testing of materials. SHPB capable of testing materials in high stress at extremely higher strain ratesSplit Hopkinson Pressure Bar Setup and Data AcquisitionHigh Speed Image Acquisition SystemStrain GaugeStrain GaugeAmplifier OscilloscopeSHPB Dynamic PVC Foam ComparisonSHPB Dynamic CNF Foam ComparisonSlide Number 24HP 250, 400 psi, strain rate: 2184 /sHP 100, 400 psi, strain rate: 2415 /sHP 200 PVC FoamHP 200 vs. HP 60 PVC FoamHP 200 vs. HP 60 PVC FoamYield Strength/Density (MPa/kg/m³)�Plateau Strength/Density (MPa/kg/m³)Elastic Modulus (MPa)Elastic Modulus/Density (MPa/kg/m³)ResultsResultsFor Both Static and Dynamic Tests:Yield Strength/Density (MPa/kg/m³)�Elastic Modulus/Density (MPa/kg/m³)ImprovementsAcknowledgements