laser ultrasonic guided wave testing of composites

Laser Ultrasonic Guided Wave

Testing of Composites

B. Boro Djordjevic

Materials and Sensors Technologies, Inc.Maryland, USA

410-766-5002, Fax. 410766-5009, www.mast-inc.com

ATA 2010 Albuquerque, New Mexico, September 19-23, 2010

Copyright Materials and Sensors Technologies, Inc, 2010

• Ultrasonic measurements are in materials plane (x/y axis) of the composite and not in thickness (z axis) direction.• Measurements utilize unconventional transducers

• laser ultrasonic wave source • air coupled receivers• miniature sub-wavelength transducers receivers.

• Tests from one side, on surface, capture full ultrasonic signatures.• Ultrasonic signals are complex guided waves

• separated into material dependent • geometry dependent • structure (path) dependent components.

• Signal amplitude and signal time resolution significantlyimproved over conventional ultrasonic, captured and analyzed with recently available digitizing capabilities, processed via new signal analysis methodology.• The measurements reported are new and cannot be reproducedusing conventional ultrasonic methodology.

TECHNOLOGY SUMMARY


OUTLINE

• Test methodology, stress waves and trunsduction

• Guided ultrasonic waves

• Non-contact ultrasonic techniques ( Hybrid systems: laser source/air detector)

• Materials characterization (Direct sensing of modulus)

• Conclusions

LASER ULTRASONIC GUIDED WAVE TESTING OF COMPOSITES


ULTRASONIC GUIDED WAVES SENSINGWITH

LASER UT SOURCE and AIR SENSORS,



Nd:YAG Laser

Data acquisition and signal processing

Charge amplifier

Lenticular array

Test panel

Air-coupled, laser or contact detector

Large Area Guided Wave (Non-contact) Ultrasonic Test Setup

Wave Source (Time 0 )

Traveling Wave

Test “Gage” Length



Adhesive fillet

Honeycomb cell wall

Skin

Skin

Skin/Core Disbond

Receive

Transmit

Guided Waves have been used for yearsto test honeycombs.Did we and do we recognize theconsequence of this application?



Directional generation of narrow-band Lamb waves

Adhesive fillet

Honeycomb cell wall

Skin

Skin

Skin/Core Disbond

Honeycomb structures detail



Disbond zone

Honeycomb Panel Tests



C-scan image of barely visible honeycomb disbondoutlined in white obtained with an acoustic microscope inpulse echo configuration.

Claudio Cosenza, at all, Johns Hopkins CNDE 2002

25

40

55

70

85

100

0.4 0.5 0.6 0.7 0.8 0.9 1

Normalized Amplitude

Scan

Pos

ition

[mm

]

Disbond zone detail

x

y

Normalized A0 signal amplitude as function of theposition along the disbond zone



Claudio Cosenza, at all, Johns Hopkins CNDE 2002

-0.35

0

0.35

10 60 110 160

Time (µsec)A

mpl

itude

(V)

-0.35

0

0.35

10 60 110 160

Time (µsec)

Am

plitu

de (V

)

0 30 60 90 120 (mm)150

30

60

90

120

(mm)

Composite Graphite/Epoxy, 165mm x 135mm x 2,7mmMask: 5 lines, λ=2mm; Air Transducer 12 Deg. Air gap 18mmSource-Receiver Distance from First Line: 48mm

Defect-12mm diameter teflon

Lamb wave composite delaminations tests

Defect

Plate



Donatella Cerniglia, at all, Johns Hopkins CNDE 2002

Lightning Test PanelTest Side

Lightning Test PanelDamage Side



80 100 120 140 160 180-40

-30

-20

-10

0

10

20

30

40

Am

plitu

de [m

V]

Time [µs]

80 90 100 110 120 130 140 150 160 170 180

-40

-30

-20

-10

0

10

20

30

40

Am

plitu

de [m

V]

Time [µs]

• Diagram of the guided wave test locations for the signal acquired in(a) damage-free zone(b) generated on the defect.

• Lightning damaged area cannot support a Lamb wave mode.• The tests were performed on the back side of the panel.

(a)

(b)




Lamb Wave Signal Change due to “Damage” Condition

Lightning strike to composite panel.Wavelet analysis




ULTRASONIC GUIDED WAVES SENSINGWITH

LASER UT SOURCE and POINT SENSORS



Nd:YAG pulsed Laser

Data acquisition and signal processing

Amplifier

Formed laser source

Test panel

Laser or contact detector

Guided wave source (Time 0 )

Traveling wave

Test “Gage” Length

Guided Wave Ultrasonic Test Setup


16

Stress-waves are mechanical phenomena, in NDE stress-waves can directly sense the mechanical state of the materials.


LASER UT GUIDED WAVE TEST CONFIGURATION FOR MODULUS AND DAMGE

Laser generation and miniature transducer receivers:• Reproducible ultrasonic source• Defines reproducible 0 time to better than 5 ns enabling time measurements and signal processing• Sub-wavelength miniature sensors resolve guidedwaveforms

Small Aperture Sensor


PIN and Miniature Transducers

Transducer Performance

Conventional angle beam transducer



TEST ASSUMPTIONS:

•SOUND VELOCITY VXY RELATES TO COMPOSITE DIRECTIONAL MODULUS VIA

EXY =k x V2XY

where k is specific materials constant

•Depending on “Guided Wave” modes, different material parameters control VXY.

•The test sample measurements' are examples of fiber and overall average plate material dominated properties.

Materials Properties Measurements


Measuring V2XY Enables Direct Sensing of the Composite Material

Elastic Modulus


GAUGE PATH, FLAT SURFACE

PATH ERROR

PATH ERROR

TIME INTERVAL ΔT in μs

DIGITIZER ERROR

FIRST ARRIVA

L

PEAK ARRIVAL

ZERO CROSSING

mm + /-mm

% ASSUMED V =10 mm/μs

+ / - 4ns + / -50 ns

% + / - 20

ns

% + / - 4 ns

200 0.1 0.10 % 20,000 0.02 % 0.25 % 0.10 % 0.04 %

150 0.1 0.13 % 15,000 0.03 % 0.33 % 0.13 % 0.053 %

100 .05 0.1 % 10,000 0.04 % 0.5 % 0.20 % 0.08 %

50 .05 0.2 % 5,000 0.16 % 1.0 % 0.40 % 0.16 %

25 .05 0.4 % 2,500 0.32 % 2.0 % 0.80 % 0.32 %

Laser generation and miniature transducer receivers:• Reproducible ultrasonic source• Defines reproducible 0 time to better than 5 ns enabling time measurements and signal processing• Sub-wavelength miniature sensors resolve guidedwaveforms

Miniature Receiver

Performance estimates for the guided wave composite characterization


Laser source:•convenient in access and non-contact•controlled stress wave source interactions•Laser source defines reproducible 0 time to better than 5 ns thusenabling signal processing



0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25

VE

LO

CIT

Y

VERTICAL LOCATION (cm )

Kevlar Bottles

NO 7 mm/usec

No 53 mm/µsec

No 61 mm/µsec

No 91 mm/µsec

Velocity maps on the sample bottles. Bottle No 61 is considered a virgin sample.



KEVLAR STRIP IN THE TENSILE LOAD FRAME

Kevlar Composite tape UT Guided Wave Velocity Tests

7.8

8

8.2

8.4

8.6

8.8

9

0 0.5 1 1.5 2

SPEE

D m

m/μ

s

PERCENT STRAIN

Kevlar Velocity Change Under Load

RUN 1, mm/μs

RUN 2, mm/μs

•Plot of sound speed as function of strain for the two test runs.•1 in grips were used to hold 1 ½ in wide strip of Kevlar material.•The overall strip length between grips was 38 cm.•Ultrasonic guided wave test path was 57.99 mm between laser source and receiving transducer roughly in the middle section of the sample.


0.01.02.03.04.05.06.07.08.09.0

0 20 40 60 80 100

VEL

OCI

TY m

m/µ

s

ANGLE Deg.

UNIDIRECTIONAL GR/E

V 1st arrival mm/µs

V 1st Peak mm/µs

0.01.02.03.04.05.06.07.08.09.0

0 20 40 60 80 100

VEL

OCI

TY m

m/µ

s

ANGLE Deg.

ISOTROPIC GR/E

V peak mm/µ

V first mm/µsec

Directional materials velocities

Directional change of V inisotropic vs unidirectional composite materials


Direct Sensing of the Composite Materials Elastic Modulus

MODULUS ( MSI) VS Velocity Square

0.0000

10.0000

20.0000

30.0000

40.0000

50.0000

60.0000

70.0000

80.0000

90.0000

0 2 4 6 8 10 12 14 16

MODULUS (KSI)

Velo

city

(Firs

t Arr

ival

) Squ

are

Series1

Plot of first arrival velocity square vs measured modulus for samples D,E,F and G


D E F G

Direct Sensing of the Composite Materials Elastic Modulus


Defect/property Characteristics

Guided Wave Sensitivity

Variable Material Property Correlation of the square of measured velocity to modulus

Porosity Velocity is slowed by porosity , frequency shift at certainwavelengths

Wrinkle Frequency shift of signals through wrinkle locations

Heat damage Velocity is slowed by heat damage, sever damage inducesmode changes and signal attenuation

Microcrack Velocity is slowed and sound is scattered at specificfrequencies by microcracks

Impact damage Velocity is slowed and guided modes changed in impactdamage regions, signal level attenuated

Complex geometry Guided wave from skin side can travel into and aroundstiffeners and be sensitive to defects

Delaminations Cause mode conversions and signal attenuation

* Table summary from Richard H. Bossi; Boeing Company;Boeing Applied Physics Lab MC2T50; 1420 S. Trenton St.; Seattle, WA 98108)

List of guided wave test responses to composite material damages or degradations*.



SUMMARYUltrasonic Testing of Advanced Composites

•Ultrasonic wave propagation in composites is unique and must be consideredfor the proper test measurements.

•Ultrasonic transduction process affects validity of test measurements for composites structures.

•A new laser ultrasonic technology has been developed for the sensing of the composite material properties.

•Laser generation, and sub-wavelength transducer sensing is critical.

•In plane guided waves can sense mechanical modulus of composite material.

•Experimental tests confirm the material properties sensing.


THE IMPACTWe can sense and measure materials information

that was considered inaccessible.

laser ultrasonic guided wave testing of composites

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