Parameter determination in damaged laminate model by optical full-field measurement of the displacement using ESPI

PARAMETER DETERMINATION IN DAMAGED LAMINATE MODEL BY OPTICAL

FULL-FIELD MEASUREMENT OF THE DISPLACEMENT USING ESPI

1

_{Institut Jean Lamour, SI2M, Nancy-Université, EEIGM 6 Rue Bastien Lepage, F-54010, Nancy, France}

_{Division of Polymer Engineering, Lulea University of Technology, SE-97187 Lulea, Sweden}

Mohamed LOUK IL

1,2

_{, Janis VARNA}

2

_{, Zoubir AYADI}

1

5

_{International Conference on Composites Testing and Model Identification}

EPFL, Lausanne, 2011

Where is Luleå?

Luleå

Where is Nancy?

Outline

Introduction : Laminate Damage

Potential of ESPI for characterizing damaged laminates

Damage development in a glass fiber/epoxy laminate

Loukil Mohamed 5th_{International Conference on Composites Testing 14}th_{February 2011}

Damage development in a glass fiber/epoxy laminate

Conclusion and perspectives

Damage in composite

debonding

Initiation (micro-scale)

Propagation (ply-scale)

Transverse cracks

Interface problem:

Direction

of propagation

Delamination

Interface problem:

Fiber/matrix

-70

°

70

°

70

°

0

°

0

°

σσσσ

σσσσ

Crack

surface

Crack surface

y

σσσσ

σσσσ

x

_→

Laminate length (Tensile axis)

y

_→

Laminate width

z

_→

Laminate thickness

COD : Crack Opening Displacement

CSD : Crack Sliding Displacement

CSD

x

y

z

.

Why we want to measure COD and CSD?

1

1

2

1

1

















−

−

+

=

ν

ν

ν

ν

E

E

h

t

COD

E

E

“Glob-Loc” approach (Janis VARNA)

COD(opening) and CSD(sliding) govern

the stiffness reduction

These parameters are calculated for 90° layer using linear

Which technique we are going to use?

These parameters are calculated for 90° layer using linear

elastic models: Shear lag, Hashins and FEM

Basic Principles of ESPI

Full Field Method: Interferometry of Speckle

ESPI

(Electronic Speckle Pattern Interferometry)

Laser

Wavelength = 0.6328 µm

Power = 30 mW

The area of study is lit by two beams coming for the same laser

9/27

Before displacement

Speckle before

displacement

x

y

After displacement

Loukil Mohamed 5th_{International Conference on Composites Testing 14}th_{February 2011}

x

y

9

=

Results Filtering Demodulating

=

1

4

5

2

3

Steps:

Speckle after

displacement

Speckle before

displacement

Fringes

map

Filtered fringes

map

Displacement

map

Displacement map

Measurement field:

about 1 cm

x

z

Loukil Mohamed 5th_{International Conference on Composites Testing 14}th_{February 2011 11}

x

y

Z

.

Advantages of ESPI

Full field imaging of displacement

with a resolution of

10 nanometers

.

Measurements can be done on a variety of materials and the displacements

under

mechanical and thermal loads

can be measured along three perpendicular axis

without

contact with the sample.

ESPI offers the unique possibility to measure both, the

in-plane and out-of-plane

displacement without surface preparation

.

Drawbacks of ESPI

Drawbacks of ESPI

Complexity

,

high costs of optical setups

,

difficulties in aligning of the optical

elements

.

There are problems in working outside the laboratory especially due to high sensitivity of

ESPI devices against environmental

vibrations and daylight

.

E

= 44.7 GPa

E

= E

= 12.7 GPa

G

= G

= 5.8 GPa

G

= 4.885 GPa

ν

= ν

= 0.297

ν

= 0.3

The [0,70

,-70

,70

,0] laminate was made of

glass fiber/epoxy.

Specimen of 19.5 mm width, the thickness is

2.75 mm and reinforced with GF/EP end tabs in

the gripping area.

Materials

0

°

+70

°

+70

°

-70

°

Z (mm)

X

Damage evolution by increasing the stress

σσσσ

13/27

-1.222 -1.375

+70

°

0

°

Crack

surface

Crack surface

y

σσσσ

σσσσ

In plane displacement measurement

CSD

RD

x

y

z

.

Measurement

direction

θ

θ

cos

sin

+

×

×

=

COD

CSD

RD

Symmetric

illuminations:

the

Relative Displacement in (-70°) layer

0

.1

8

9

µ

m

1

9

6

µ

m

RD

=0.380 µm/MPa

Crack 1

Crack 2

R

e

la

ti

v

e

D

is

p

la

c

e

m

e

n

t

(µ

m

)

0

.1

8

9

µ

m

1

9

6

µ

m

Loukil Mohamed 5th_{International Conference on Composites Testing 14}th_{February 2011}

0

.1

9

6

_RD

=0.380 µm/MPa

RD

=0.394 µm/MPa

x

z

R

e

la

ti

v

e

D

is

p

la

c

e

m

e

n

t

Pixels

Profile of the X-direction relative displacement along the mid-plane (on the specimen

edge) corresponding to a variation of the relative average stress (

_∆

σ

= 0.497MPa).

0

.1

9

Relative Displacement in (70°) layers

R

e

la

ti

v

e

D

is

p

la

c

e

m

e

n

t

(µ

m

)

Relative displacement profile along the X-axis in the midplane of the 70°ply. (

_∆

σ

= 0.497 MPa)

0°

70°

-70°

R

e

la

ti

v

e

D

is

p

la

c

e

m

e

n

t

Pixels

x

z

Relative Displacement in (0°) layers

R

e

la

ti

v

e

D

is

p

la

c

e

m

e

n

t

(µ

m

)

Relative displacement profile along the X-axis in the midplane of the 0°ply. (

_∆

σ

= 0.497 MPa)

Loukil Mohamed 5th_{International Conference on Composites Testing 14}th_{February 2011}

0°

70°

70°

0°

-70°

R

e

la

ti

v

e

D

is

p

la

c

e

m

e

n

t

Pixels

x

z

Out of plane displacement measurement

CSD

Crack

surface

Crack surface

RD

y

z

.

σσσσ

σσσσ

Non Symmetric illuminations:

the measurement is

perpendicular to the fiber

RD

x

.

Measurement

direction

Bisector

Crack 1

Crack 2

COD

= 0.300 µm/MPa

1

6

6

µ

m

0

.1

6

0

µ

m

R

e

la

ti

v

e

D

is

p

la

c

e

m

e

n

t

(µ

m

)

COD measurement

Loukil Mohamed 5th_{International Conference on Composites Testing 14}th_{February 2011}

Profile of the X-direction COD along the mid-plane (on the specimen edge)

corresponding to a variation of the relative average stress (

_∆

σ

= 0.533MPa).

COD

=0.311 µm/MPa

0

.1

6

6

R

e

la

ti

v

e

D

is

p

la

c

e

m

e

n

t

Pixels

x

z

RDn

CODn

CSDn

COD/CSD

Crack 1

0.380

0.300

0.286

1.049

Crack 2

0.394

0.311

0.297

1.047

Comparison of COD and CSD

For (-70°) layer

θ

θ

cos

sin

+

×

×

=

COD

CSD

RD

θ

θ

cos

sin

COD

DR

CSD

=

−

Interactive cracks

RD

= 0.200 µm/MPa

RD

= 0.299 µm/MPa

RD

= 0.313 µm/MPa

RD

= 0.257 µm/MPa

Crack 1

Crack 2

Crack 3

Crack 4

R

e

la

ti

v

e

D

is

p

la

c

e

m

e

n

t

(µ

m

)

Loukil Mohamed 5th_{International Conference on Composites Testing 14}th_{February 2011}

RD

= 0.257 µm/MPa

Profile of the X-direction COD along the mid-plane (on the specimen edge)

corresponding to a variation of the relative average stress (

_∆

σ

= 0.569MPa).

R

e

la

ti

v

e

D

is

p

la

c

e

m

e

n

t

Pixels

0,010 0,015 0,020

C

O

D

(

m

m

)

Crack Opening Displacement in (-70°) layer by FEM

[0, 70

, -70

]

0.25 _{Experimental points}

Elliptical model (fitted)

0,000 0,005 0,010 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7

C

O

D

(

m

m

)

Elliptical Profile

Actual Crack Profile = Elliptical Profile

0.05 0.1 0.15 0.2 0 5 10 15 20 25

z (pixels)

C

O

D

(

µ

m

)

)

(

1

)

0

(

)

(

a

z

COD

z

COD

=

−

Elliptical model

Conclusion

ESPI Potential for characterizing damage in laminates

Displacement field on the edge of a cracked laminate

Typical profile the displacement for each ply

Displacement jumps (cracks) can be measured,

Loukil Mohamed 5th_{International Conference on Composites Testing 14}th_{February 2011}

By changing the directions of laser beams, the COD is directly

measured; the comparison between COD and CSD is done in this

work.

The ratio COD/CSD depends on the material and on the ply

orientation.

Perspectives

Comparison with micromechanics models.

Investigate the effect of interaction between cracks

Delamination effect on COD

Thank you for

your attention!

your attention!

Camera

θθθθ

θθθθ

2

Δx

δ

M’

M

∆x

λ

)

(

π

δ

λ

π

δ

λ

π

θ

φ

=

2

₁

+

2

₂

=

4

sin

∆

θθθθ

1

1’

M’