Certification of Discontinuous Composite Material Forms for Aircraft Structures

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Certification of Discontinuous Composite

Material Forms for Aircraft Structures

Paolo Feraboli (UWAA), Mark Tuttle (UW), Larry Ilcewicz (FAA),

Bill Avery (Boeing), Bruno Boursier, Dave Barr (Hexcel)

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Aluminum Clamps Pivots Bottom Load Point HexMC Angle Strain Gage Wiring

to Data Acquisition System Steel Linkages Top Load Point

Tuttle and Shifman

Angle beams with 3 different flange lengths were

tested:

•

3.5 inch (Large Angle Beam, 4 plies)

•

2.5 inch (Medium Angle Beam, 4 plies)

•

1.75 inch (Small Angle Beam, 2 plies)

Four point bending loads were applied to the

Test 1: 0°

+z

+y

+z

Test 2: ‐135° (unsymmetric)

+z

+y

Test 3: ‐45° (unsymmetric) 3 5,6 2 7,8

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Beam Theory

Distances from centroid to extremities of angle beam and moments of inertia:

t a yc zc z (major principal centroidal axis) y (minor principal centroidal axis)

T

M

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Shell elements with MPC

y

x

z

Centroidal axis

Section at C1 & C2

M

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FEM Analysis (Orthotropic/ Quasi-Isotropic Tape)

Typical Strain behavior showing match

between model & beam theory with an

Longitudinal Strain (x-direction)

Orthotropic mechanical

properties:

5.97

0.28

1.8 Average values

for

&

based

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Normalized Strain Curves

EMIN

EAVG

EMAX

Highlighted region is admissible for HexMC based on modulus

variability

EAVG=5.97 EMAX=8.68

Normalized strain is a function of 1/E, hence non linear

EMIN=4.12

Typical Plot of Results

,

∝

1

• ,

,

: three different values for

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Comparison between Experiment and Simulation (Large Angle

Beams, 0 degree)

EMIN EAVG EMAX E BEST FIT

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Comparison between Experiment and Simulation (Large Angle Beams, 180 degree)

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Comparison between Experiment and Simulation (Large Angle Beams,90 degree)

EMIN EAVG

EMAX

E BEST FIT

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Comparison between Experiment and Simulation (Large Angle Beams, -90 degree)

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Comparison between Experiment and Simulation (Large Angle Beams, -45 degree)

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Comparison between Experiment and Simulation (Large Angle Beams,-135 degree)

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Comparison between Experiment and Simulation (Medium Angle Beams, 0 degree)

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Comparison between Experiment and Simulation (Medium Angle Beams,180 degree)

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Comparison between Experiment and Simulation (Medium Angle Beams,90 degree)

EMIN EAVG

EMAX

E BEST FIT

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Comparison between Experiment and Simulation (Medium Angle Beams,-90 degree)

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Comparison between Experiment and Simulation (Medium Angle Beams, -45 degree)

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Comparison between Experiment and Simulation (Medium Angle Beams, -135 degree)

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Comparison between Experiment and Simulation (Small Angle Beams, 0 degree)

EMIN EAVG EMAX EBEST FIT

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Comparison between Experiment and Simulation (Small Angle Beams, 180 degree)

EMIN EAVG EMAX EBEST FIT

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Comparison between Experiment and Simulation (Small Angle Beams, 90 degree)

EMIN EAVG

EBEST FIT

EMAX

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Comparison between Experiment and Simulation (Small Angle Beams, -90 degree)

EMIN EAVG EBEST FIT EMAX

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Comparison between Experiment and Simulation (Small Angle

Beams, -45 degree)

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Comparison between Experiment and Simulation (Small Angle

Beams, -135 degree)

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Modulus Best Fit

Angle [

̊

]

Modulus [Msi]

(Large Angle Beam)

Modulus [Msi]

(Medium Angle Beam)

Modulus [Msi]

(Small Angle Beam)

0

4.93

5.71

11.9

180

4.89

5.62

12.1

90

5.41

5.87

11.2 -90

5.48

6.07

11.5 -45

6.17

5.52

11.8 -135

5.13

6.61

12.4 AVG

5.33

5.90

11.8 CoV

9%

7%

4%

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FEM Analysis (Randomized Orthotropic)

• The models were discretized in:

- 312 RRVE for the large angle beam

- 216 RRVE for the medium angle beam

- 168 RRVE for the small angle beam

• Each RRVE has elastic orthotropic material properties assigned independently

from the neighboring ones and generated by running the stochastic laminate

analogy code in Matlab.

• The discretization of the specimen into RRVE’s has no relation with the mesh size.

The nodes of neighboring RRVE’s are merged to ensure displacement compatibility.

• For each geometry (large, medium, small):

• 30 FEM runs

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Modulus: Global Properties & Distribution

Overall Modulus

MAX [Msi] AVG [Msi] MIN [Msi]

9.18 6.34 3.96

Global properties same as orthotropic with EAVG

x-x y-y 1 2 3 4 5 6 7 Section Modulus

RRVE # _{Section x-x [Msi]}Modulus at _{Section y-y [Msi]}Modulus at 1 6.57 6.64 2 6.63 5.15 3 6.44 5.44 4 5.92 6.77 5 5.16 4.33 6 5.99 5.52 x-x

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Large Angle Beam: Max, Avg, Min @ SG #1 (0 degree)

FEM prediction of strain values with QI Tape approach (MIN, AVG, MIN

predicted modulus) FEM prediction of strain values

with stochastic approach (MIN, AVG, MAX over 30 runs)

NOTE:

Experimental strain value

falls OUTSIDE of range of

random

prediction

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Large Angle Beam: Max, Avg, Min @ SG #2 (0 degree)

FEM prediction of strain values with QI Tape approach (MIN, AVG, MIN

NOTE:

Experimental strain value

falls OUTSIDE of range of

random

prediction

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Large Angle Beam: Max, Avg, Min @ SG #3 (0 degree)

FEM prediction of strain values with QI Tape approach (MIN, AVG,

MAX predicted modulus) FEM prediction of strain values

NOTE:

Experimental strain value

falls INSIDE of range of

random

prediction

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Large Angle Beam: Max, Avg, Min @ SG #4 (0 degree)

MAX predicted modulus) FEM prediction of strain values

NOTE:

Experimental strain value

falls OUTSIDE of range of

random

prediction

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Large Angle Beam: Max, Avg, Min @ SG #5 (0 degree)

MAX predicted modulus) FEM prediction of strain values with

stochastic approach (MIN, AVG, MAX over 30 runs)

NOTE:

Experimental strain value

falls INSIDE of range of

random

prediction

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Large Angle Beam: Max, Avg, Min @ SG#6 (0 degree)

FEM prediction of strain values with QI Tape approach (MIN, AVG, MAX

NOTE:

Experimental strain value

falls INSIDE of range of

random

prediction

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Medium Angle Beam: Max, Avg, Min @ SG#1 (0 degree)

FEM prediction of strain values with stochastic approach (MIN,

AVG, MAX over 30 runs)

MAX predicted modulus)

NOTE:

Experimental strain value

falls INSIDE of range of

random

prediction

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Medium Angle Beam: Max, Avg, Min @ SG#2 (0 degree)

FEM prediction of strain values with QI Tape approach (MIN, AVG, MAX

NOTE:

Experimental strain value

falls INSIDE of range of

random

prediction

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Medium Angle Beam: Max, Avg, Min @ SG#3 (0 degree)

MAX predicted modulus)

NOTE:

Experimental strain value

falls INSIDE of range of

random

prediction

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Medium Angle Beam: Max, Avg, Min @ SG#4 (0 degree)

NOTE:

Experimental strain value

falls OUTSIDE of range of

random

prediction

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Medium Angle Beam: Max, Avg, Min @ SG#5 (0 degree)

NOTE:

Experimental strain value

falls INSIDE of range of

random

prediction

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Medium Angle Beam: Max, Avg, Min @ SG#6 (0 degree)

NOTE:

Experimental strain value

falls INSIDE of range of

random

prediction

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Medium Angle Beam: Max, Avg, Min @ SG#7 (0 degree)

NOTE:

Experimental strain value

falls INSIDE of range of

random

prediction

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Medium Angle Beam: Max, Avg, Min @ SG#8 (0 degree)

NOTE:

Experimental strain value

falls OUTSIDE of range of

random

prediction

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Conclusions

• Prediction based on orthotropic (quasi isotropic) layered with E

₁

=E

₂

=E

_AVGEXPER

are not

sufficient

• All data points fit in the admissible region for the large & medium beams. Small beams fall

outside region. Admissible region based on EMAX, EAVG, EMIN obtained from

experiments

• E

_BESTFIT

shows non negligible error in prediction of elastic response if using E

_AVGEXPER

• Need to define a suitable E for the material (statistical B-basis value?)

• For small beams (2 plies), predictions are too off to be due to normal variability. Different

explanations exist, confirmation will follow.

• If multiple beams of same size are tested, different results are expected. So far only 1

beam per geometry and orientation has been strain gaged & tested. Not possible to

measure the variability of the same location strain over multiple specimens.

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