Numerical simulation of mid-IR ultrasound testing in CFRP

Kanae Oguchi1*, Manabu Enoki1

Hisashi Yamawaki2, Masahiro Kusano2, Makoto Watanabe2

1Department of Materials Engineering, The University of Tokyo, Japan

2Optical & Electronic Materials Unit, National Institute for Materials Science (NIMS), Japan

Contents

Mid-IR LUT system

• Sample surface effect on ultrasonic wave

• Computer simulation

Computer simulation of non-linear ultrasound method for closed defect

Carbon-fiber-reinforced plastic(CFRP)

Laser ultrasound Testing

• Non-contact operation • Non Destructive Testing • Freedom in shape of sample

Feature of LUT

• Smaller light weight solid state light source which generate a ultrasound efficiently in CFRP is desirable !

Conventional ultrasound laser sources

Dubois et al. ultrasonics, Vol40-p809 (2002)

Suitable wavelength of a laser for LUT in CFRP

Wavelength of 3.2mm seems the best !

Developed a 3.2 mm laser by wavelength conversion device

CO2 Laser

• 3.2 mm laser is NOT available in the market

Optical depth vs. Laser wavelength

Wavelength conversion by OPO

-Z

Y 5m

m

+Z

Periodically-poled structure of wide aperture device Optical Resonator

PP-MgSLT crystals

(NIMS-original device)

Mid-IR LUT system

Contents

Mid-IR LUT system

• Sample surface effect on ultrasonic wave

• Computer simulation

Computer simulation of non-linear ultrasound method for closed defect

Sample surface effect

Mid-IR YAG

epoxy thickness[mm] 0-130 0-130

Fluence[J/cm2] 0.051 0.059

Without Coating With Epoxy coating

Wave detection point

Sample surface effect

YAG Mid-IR

Without coating

40mm-t coating

• Epoxy coating increase the amplitude of ultrasonic

• Mid-IR laser can generate the strong ultrasonic compare to the YAG laser

• ultrasonic amplitude increased with the epoxy thickness until around 50μm and reached to a constant value

• maximum amplitude of YAG laser was less than half of the mid-IR laser

C-scan Images with mid-IR laser

C-scan images of the CFRP samples including the PTFE plate

• Coated sample shows the significant SNR improvement !

5mm 1mm

Artificial defect (PTFE)

Without coating 40mm coating

Contents

Mid-IR LUT system

• Sample surface effect on ultrasonic wave

• Computer simulation

Computer simulation of non-linear ultrasound method for closed defect

Ultrasound testing for closed defect

• traditional ultrasonic techniques are only sensitive to open defects

defects in laminar composites where the surfaces of the laminates are in close physical contact with each other, but there is little to no bonding strength between the surfaces

Non-Linear ultrasound method

delamination

Open crack

Micro crack

Kissing bonds

Kissing bonds

various type of defect in CFRP

Non-linear ultrasound method

conventional method

Non-Linear ultrasound method

transmitting Incident wave

Frq.

Amp.

A

Open defect

f

f

A

f

closed defect

closed defect

Defect!

Without Defect

f0

A0

A0

A0

f0

f0 f2 f3

f

A

Defect!

Large amplitude wave

f0

f0

f0 fundamental component

f2 2nd harmonic component f3 3rd harmonic component

Amplitude Change

Frequency Change

A1

Elastic

wave

Non-linear elastic response

Previous report:

Fatigue damage

1D solid model with closed defect

Unit cell with

closed defect T, C, r, S V, d

Strain of unit cell with closed defect

Elastic

wave

Compressive stress, Tcomp≦ 0

0/ CTS compc

0cS

0cS

0cS

)0( compTS : strain

T : stress

C : stiffness

Input signal

Governing Equation

Material Properties for Fe

r=7650,C=274GPa

x

T

t

v

r

x

vC

t

T

C=0 T=0

C=C0

Input signal :

Frequency, f: 5MHz

)2cos(2/ ftTamp

Tamp : -1Pa -100Pa

2D simulation with closed defect

2D solid model with closed defect of 4mm

Incident signal： frequency: 5MHz, wavelength: 1.2mm, amplitude: -3Pa

500×500, Δx=40μm, Δt=2.5ns

Displacement wave foam

Transmission wave

Incident wave

Time (s)

Dis

pla

ce

me

nt (m

)

2D simulation

Incident signal： frequency: 5MHz, wavelength: 1.2mm, amplitude: -3Pa

500×500, Δx=40μm, Δt=2.5ns

conclusion

• The epoxy coating on CFRP sample surface dramatically

increase the ultrasound amplitude which lead to the significant

SNR improvement

• Maximum amplitude of ultrasound generated by mid-IR lase is

abut twice the size of that by YAG laser.

• Laser ultrasound propagation model in CFRP laminate with

epoxy coating is developed, and the simulation results is good

agreement with the experimental data.

• 2D solid model with closed defect is developed, and confirmed

the saw-like shaped transmission wave containing the second

and third harmonic component.