Fundamental Studies in Embedded Ultrasonic NDE

Victor Giurgiutiu

University of South CarolinaColumbia, SC 29208

AFOSR Grant FA9550-04-0085: 3/2004—12/2006

Air Force Office of Scientific Research Contractors’ Meeting

Structural Mechanics

Wintergreen, Virginia, 18-20 August 2004

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Structural Health Monitoring (SHM)

Passive SHM: records flight parameters, loads, strain, environment, vibrations, acoustic emission from cracks, etc.

Active SHM: detects damage, cracks, disbonds, delaminations, etc. (embedded ultrasonic NDE)

SHM Research Aim: Develop embedded sensors for active SHM

(Giurgiutiu, V.; Zagrai, A. N.; Bao, J. “Piezoelectric Wafer Embedded Active Sensors for Aging Aircraft Structural Health Monitoring”, Structural Health Monitoring – An International Journal, Sage Pub., Vol. 1, No. 1, July 2002, pp. 41-61 )

Data concentrator

Structural health monitoring unit

Active sensors cluster 2

Data concentrator

Active sensors cluster 3

Active sensors cluster 4 Active

sensors cluster 1

3

Rivet head

Piezoelectric Wafer Active Sensors (PWAS)

PIEZO ELEMENT

Conventional ultrasonic transducer

PWAS

P-wave

t

PWAS ~ V(t)

Lamb wave

t

/2

7 mm

4

Non-dispersive (S0) Wave Propagation

5

Dispersive (A0) Wave Propagation

6

State of the Art Chang et al. (Stanford)

Inman et al. (Virginia Tech)

Yuan et al. (NC State)

Cesnik et al. (Michigan)

Adams et al. (Purdue)

Kessler & Spearing (MIT)

Cawley, Soutis, Culshaw, et al. (UK: Imperial College, Sheffield…)

Boller et al. (Germany: EDAS UK: Sheffield)

Balageas et al. (France: ONERA, CNAM, INSA, …)

Galea, Ye et al. (Australia)

…

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Pitch-Catch Crack Detection in Metallic Plate

(T)

(R)

(Ihn, J.-B.; Chang, F.-K. (2002) “Built-in Diagnostics for Monitoring Crack Growth in Aircraft Structures”, Proceedings of the SPIE 9th International Symposium on Smart Structures and Materials, 17-21 March 2002, San Diego, CA, paper #4702-04 )

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Pitch-Catch Detection of Composite Damage

Lemistre, M.; Osmont, D.; Balageas, D. (2000) “Active Health System Based on Wavelet Transform Analysis of Diffracted Lamb Waves”, SPIE Vol. 4073, 2000, pp. 194-202

Wang, C. S.; Chang, F.-K. (1999) “Built-In Diagnostics for Impact Damage Identification of Composite Structures”, in Structural Health Monitoring 2000, Fu-Kuo Chang (Ed.), Technomic, 1999, pp. 612-621

Su, Z.; Ye, L. (2004) “Fundamental Lamb Mode-based Delamination Detection for CF/CP Composite Laminates Using Distributed Piezoelectrics”, Structural Health Monitoring – An International Journal, Vol. 3, No. 1, March 2004, pp. 43-68

Signal processing

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Pulse-Echo Detection of Composite Damage

(Diaz Valdes, S. H.; Soutis C. (2002) “Real-Time Nondestructive Evaluation of Fiber Composite Laminates Using Low-Frequency Lamb Waves”, Journal of the Acoustical Society of America, May 2002, Volume 111, Issue 5, pp. 2026-2033)

• Carbon fiber/epoxy composite

[±45/0/90]3s

• Impact damage

• 15 KHz flexural waves

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Embedded Ultrasonics Structural Radar (EUSR)

• Broad-side crack specimen: Φ0=90°; R=305 mm• Off-side crack specimen: Φ0=135°; R=431 mm

9-element PWAS array

Data acquisition

TDS-210 digital oscilloscope

Aluminum plate specimen

HP-33120A signal

generator

(Giurgiutiu, V.; Bao, J. “Embedded-Ultrasonics Structural Radar for the Nondestructive Evaluation of Thin-Wall Structures” 2002

ASME International Mechanical Engineering Congress, November 17-22, 2002, New Orleans, LA, paper # IMECE2002-39017)

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EUSR: Broadside Crack Detection

Result from the EUSR algorithm mapping the upper half of the plate

and the crack location

crack

20mm Slit

1220-mm sq., 1-mm thick 2024 T3 (48-in sq., 0.040-in thick)

PWAS array

Square plate specimen with 9-element PWAS array at its center

(Giurgiutiu, V.; Bao, J. “Embedded-Ultrasonics Structural Radar for the Nondestructive Evaluation of Thin-Wall Structures” 2002

ASME International Mechanical Engineering Congress, November 17-22, 2002, New Orleans, LA, paper # IMECE2002-39017)

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EUSR: Offside Crack Detection

crack20mm Slit

1220-mm sq., 1-mm thick 2024 T3 (48-in sq., 0.040-in thick)

PWAS array

Result from the EUSR algorithm mapping the upper half of the plate

and the crack location

Square plate specimen with 9-element PWAS array at its center(Giurgiutiu, V.; Bao, J. “Embedded-Ultrasonics Structural Radar for the Nondestructive Evaluation of Thin-Wall Structures” 2002

ASME International Mechanical Engineering Congress, November 17-22, 2002, New Orleans, LA, paper # IMECE2002-39017)

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Detection of Pin Hole with EUSR Pin-hole damage of increasing size was detected with the

EUSR method

Pin-hole sizes: d1 = 0.5 mm d2 = 1.0 mm d3 = 1.57 mm d4 = 2.0mm

PWAS array

1.57 mm pin-hole

2 mm pin-hole

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Proposed Research Relevancy

Objective: Understanding the Lamb-wave interaction between piezoelectric wafer active sensor (PWAS) and aerospace structure:– Multiple mode-tuning of Lamb waves with broadband PWAS transducers– In-situ immittance of PWAS transducers

State of the art: PWAS have been used experimentally in several laboratory applications; fundamental studies are still needed

Approach: – Advanced modeling of the mechano-electrico-acoustical interaction – Energy transfer optimization for various Lamb-wave modes– Electromechanical impedance of the PWAS interacting with the Lamb-waves– Space-domain Fourier transform solutions with broadband simulations– Experimental verification of the models and theoretical predictions

Systems to benefit from research: present and future USAF systems

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Background Information and Partnerships

Past history in the field:– Chang et al. (Stanford); Inman et al. (Virginia Tech); Yuan et al. (NC State);

Cesnik et al. (Michigan); Adams et al. (Purdue); Kessler & Spearing (MIT); Cawley, Soutis, Culshaw, et al. (UK: Imperial College, Sheffield Univ.); Boller et al. (Germany: EDAS; UK: Sheffield Univ.); Balageas et al. (France: ONERA, CNAM, INSA, …); Galea, Ye et al. (Australia)

– Giurgiutiu et al. (South Carolina): PWAS modeling and experiments

Collaborators:– Other USAF projects:

• AFRL: “Structural Monitoring with Piezoelectric Wafer Active Sensors”– Other government agencies

• NSF: “Predictive Methodologies for the Design of Lamb-Wave Piezoelectric Wafer Active Sensors for Structural Health Monitoring, Damage Detection, and Failure Prevention”

– Relevant international research projects• University of Sheffield, UK and University of Patras, Greece:

“European Collaboration on Structural Health Monitoring Sensors”

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Innovation in Science - I

What makes the research unique:– Embedded Lamb mode tuning and in-situ PWAS immittance using

analytical modeling, numerical simulation, and experimental validation with harmonic/Bessel functions and space-domain Fourier/Hankel transforms

How is it different from what has been done in the past:– Electro-acoustic transfer function of the transmitting and receiving PWAS

transducers is determined from a coupled-fields analysis of the mechanical stress/strain and the electrical voltage/current in Lamb-wave formulation

ta

t

tb

PWAS

-a +a

x

0 ( ) i tx e y=+d

y=-d

PW AS, 0.2-m m thick

Substrate structure 1-m m thick

Bond layer

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Innovation in Science - II

Scientific success story:– Preliminary studies performed in

2-D coordinates have been confirmed by experimental results

Scientifically “new”:– Unique modeling-experimental

analysis for behavior prediction

h =

2d

/2

PWAS ~ V(t)

S0 Lamb mode

Res

pons

e, m

V

0 20 40 60 80

100 120 140 160

0 100 200 300 400 500 600Frequency, kHz

S0 mode

A0 modeExperiment

0 100 200 300 400 500 6000

0.5

1

f, kHz

No

rmal

ized

str

ain

S0

A0

Theory

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Problems to be addressed– Adhesive interface between the PWAS and the structure

• Shear wave transmission• Durability and survivability

– Lamb wave tuning effects:• PWAS geometric effects• PWAS material properties effects• “Dial-up” the Lamb wave modes

– In-situ PWAS immittance• Prediction of the electro-acoustical transfer function• Correlation of immittance peaks with Lamb wave tuning

Approach:– Analytical modeling:

• Space-domain Fourier and Hankel transforms• Closed form and series solutions

– Numerical simulation• Advanced finite elements

– Experimental confirmation• Coupon specimens• Realistic specimens (as available)

Proposed Work

0

10

20

30

40

200 1000 1800 2600Frequency, kHz

Re

Z, O

hms

Sensor 1

Sensor 2

Sensor 3

Sensor 4

Experimental Lamb-mode ReZ impedance peaks

x

y uxuy

S0 @ 1,000 kHz

x

y

ux

uy

S0 @ 3,000 kHz

x

yux uy

S1 @ 3,000 kHz

Plat

e th

ickn

ess

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Innovation in Design

Hardware or design methodology improved as a result of the research:– Comprehensive modeling and analysis of the

interaction between PWAS transducers and Lamb-waves in aerospace structures structural health monitoring

Research results implementation:– Integrated health monitoring of current and

future aerospace systems

Data concentrator

Structural health monitoring unit

Active sensors cluster 2

Data concentrator

Active sensors cluster 3

Active sensors cluster 4 Active

sensors cluster 1