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Elastic Properties of K13D2U/Epoxy Prepreg

Mark E. Tuttle, University of Washington

tuttle@u.washington.edu

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Elastic Properties of K13D2U/Epoxy Prepreg Preliminary Comments

Current design of L0 support structure involves a six-ply [0/20/-20]s laminate (used in outer castellated shell) and a three-ply [0/90/0] laminate (used in inner cylindrical tube)

The elastic properties of the [0/20/-20]s and [0/90/0] laminates will differ substantially

By measuring the in-plane properties listed below for an individual ply, in-plane elastic properties of any multi-angle laminate can be predicted using lamination theory:E1 and E2 (moduli parallel and perpendicular to fiber direction)

12 (“major” Poisson ratio)

G12 (shear modulus)

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Elastic Properties of K13D2U/Epoxy Prepreg Objectives

To measure unidirectional properties (E1, E2, 12, and G12) exhibited by the K13D2U/epoxy composite delivered by Fermilab to the UW

Use lamination theory to predict Ex and xy exhibited by a [0/20/-20]s laminate

To compare predictions to measurements obtained using a [0/20/-20]s tensile specimen machined from a prototype castellated outer shell

(…subsequently, updated FEA analyses of the L0 support structure was performed by C.H. Daly, based on measured elastic properties)

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Technical ApproachMeasurement of unidirectional properties

E1 and 12: Measured using biaxial strain gages rosettes, mounted back-to-back on a [0]6 tensile specimen

E2: Measured using uniaxial strain gages, mounted back-to-back on a [90]6 tensile specimen

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22

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Technical ApproachMeasurement of unidirectional properties

G12: Measured using biaxial strain gages rosettes, mounted back-to-back on a [45/-45]s tensile specimen

(This technique described in Whitney, Daniel, Pipes, Experimental Mechanics of Fiber Reinforced Composite Materials, Chapter 4, ISBN 0-912053-01-1)

xx

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Technical ApproachMeasurement of Ex and xy for [0/20/-20]s laminate

Ex and xy: Measured using biaxial strain gages rosettes, mounted back-to-back on a [0/20/-20]s tensile specimen machined from prototype outer castellated shell

xx

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Preparation of [0]6, [90]6, and [45/-45]s Specimens

Three flat rectangular panels with required stacking sequences were prepared using a Tetrahedron MTP Programmable Hot Press

One surface of the panels was adjacent to an aluminum plate coated with release agent (the “tool” side), while the opposite surface was adjacent to a porous teflon release ply (the “fabric” side)

Cure cycle imposed using the hot press (pressure, temperature, time) simulated the autoclave cure cycle used to produce prototype outer and inner shells

Tensile specimens were machined from these panels using a diamond-coated abrasive cut-off wheel

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Specimen Preparation - Unidirectional Tests

(Nominal) physical dimensions: [0]6 specimens: 0.0140 x 0.7450 x 7 in

[90]6 specimens: 0.0140 x 0.7450 x 6 in

[45/-45]s specimens: 0.0120 x 0.7450 x 6 in Comments:

Nominal ply thickness was 0.0024 in for [0]6 and [90]6 specimens and 0.0030 for [45/-45]s specimens

To conserve material, specimens were much thinner than is “customary”, and aspect ratios did not meet ASTM specification of 10-12

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Test Equipment

Instron Model TM-M-L table-top test frame

Vishay Series 2100 strain gage amplifiers

Mac IIci equipped with National Instruments A/D board and LabView Software package

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[0]6 Specimen

[0]6 - Specimen 4 - Raw Data

0

100

200

300

400

500

600

-600 -400 -200 0 200 400 600 800 1000

Strain (min/in)

Loa

d (l

bf) Axial Strain (Fabric)

Trans Strain (Fabric)

Axial Strain (Tool)

Trans Strain (Tool)

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[0]6 Specimen

[0]6 Specimen 4 - Stress-Strain Curves

0

10000

20000

30000

40000

50000

60000

-600 -400 -200 0 200 400 600 800 1000

Strain (min/in)

Str

ess

(psi

) Axial Strain (Fabric)

Trans Strain (Fabric)

Axial Strain (Tool)

Trans Strain (Tool)

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[0]6 Specimen

[0]6 Specimen 4

0

10000

20000

30000

40000

50000

60000

0 100 200 300 400 500 600 700 800 900

Average Axial Strain (min/in)

Str

ess

(psi

)

E1 = 59.5 Msi

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[0]6 Specimen

[0]6 Specimen 4

0

50

100

150

200

250

300

350

0 100 200 300 400 500 600 700 800 900

Ave Axial Strain (min/in)

-1*A

ve T

rans

Str

ain

(in

/in)

12 = 0.39

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[90]6 Specimen

[90]6 Specimen 2

-200

0

200

400

600

800

1000

1200

1400

-500 0 500 1000 1500 2000 2500

Strain (min/in)

Str

ess

(psi

)

Axial Strain (Fabric)

Axial Strain (Tool)

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[90]6 Specimen

[90]6 Specimen 2

-200

0

200

400

600

800

1000

1200

1400

-200 0 200 400 600 800 1000 1200 1400 1600 1800

Average Axial Strain (min/in)

Str

ess

(psi

)

E2 = 0.806 Msi

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[45/-45]s Specimen

[45/-45]s Specimen 3 - Stress-Strain Curves

0

1000

2000

3000

4000

5000

-3000 -2000 -1000 0 1000 2000 3000

Strain (min/in)

Str

ess

(psi

) Axial Strain (Fabric)

Axial Strain (Tool)

Trans Strain (Fabric)

Trans Strain (Tool)

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[45/-45]s Specimen

[45/-45]s Specimen 3

0

1000

2000

3000

4000

5000

0 500 1000 1500 2000 2500

Average Axial Strain (min/in)

Str

ess

(psi

)

Ex = 2.32 Msi

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[45/-45]s Specimen

[45/-45]s Specimen 3

-500

0

500

1000

1500

2000

-500 0 500 1000 1500 2000 2500

Average Axial Strain (min/in)

-1*A

ve T

rans

Str

ain

(in

/in)

xy = 0.95

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[45/-45]s SpecimenCalculation of G12

The shear modulus implied by these measurements is*:

(Whitney, Daniels, Pipes, Experimental Mechanics of Fiber Reinforced Materials, Chapter 4, ISBN 0-912053-01-1)

MsiMsiE

Gxy

x 595.0)95.1(2

32.2

)1(212

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Summary of Measured Unidirectional Properties and Predictions for a [0/20/-20]s Laminate

Summary of measured unidirectional properties:

E1 = 59.5 Msi 12 = 0.39

E2 = 0.806 Msi G12 = 0.595 Msi

Predicted properties for a [0/20/-20]s laminate:

Ex = 38.4 Msi xy = 3.0

Ey = 1.08 Msi Gxy = 4.55 Msi

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[0/20/-20]s Specimen

[0/20/-20]s Laminate

0

5000

10000

15000

20000

25000

30000

35000

-3000 -2000 -1000 0 1000

Strain (min/in)

Str

ess

(psi

) Axial Strain (Fabric)

Trans Strain (Fabric)

Axial Strain (Tool)

Trans Strain (Tool)

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[0/20/-20]s Specimen(Predicted Ex = 38.4 Msi)

[0/20/-20]s Laminate

0

5000

10000

15000

20000

25000

30000

35000

0 100 200 300 400 500 600 700 800

Average Axial Strain (min/in)

Str

ess

(psi

)

Ex = 43.7 Msi

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[0/20/-20]s Laminate

0

500

1000

1500

2000

2500

0 100 200 300 400 500 600 700 800

Average Axial Strain (min/in)

-1*A

ve T

rans

Str

ain

(in

/in)

xy = 3.1

[0/20/-20]s Specimen(Predicted xy = 3.0)

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Sensitivity StudyVariation in Exx for [0/+/-]s Laminates

20

25

30

35

40

45

50

55

60

65

0 5 10 15 20 25 30 35 40

Angle (degrees)

Axi

al M

odul

us E

xx (

Msi

)

Predicted

Measured

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Sensitivity StudyVariation in xy for [0/+/-]s Laminates

0.35

0.85

1.35

1.85

2.35

2.85

3.35

0 10 20 30 40

Angle (degrees)

Poi

sson

Rat

io,

xy

Predicted

Measured

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Sensitivity StudyVariation in Eyy and Gxy for [0/+/-]s Laminates

0

2

4

6

8

10

12

0 5 10 15 20 25 30 35 40

Angle (degrees)

Mod

uli

(Msi

)

Eyy

Gxy

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Discussion

Only one measurement has been made for all specimen types; results obtained are not valid in a statistical sense

Specimen thickness is smaller than is customary, and in-plane aspect ratios are lower than ASTM specifications

Nevertheless, comparisons between measurement and prediction for a [0/20/-20]s laminate are reasonable

Given material costs, measured properties are sufficient for present purposes