Acoustic Characterization of Materials

Bernhard R. TittmannGroup Leader

Francesco CostanzoClifford Lissendon

Joseph RoseBrian ReinhardtManton Guers

CAV

Acoustic Characterization of Materials

Current Projects:

1. “Ultrasonic High Temperature Phased Array” Bechtel Bettis

2. “Sensor Fabrication and Testing for In-Situ Operation of NDE” PNNL.

3. “Signal Enhancements to Ultrasonic Spray-on Technology” EPRI

CAV

Air-coupled Non-Contact Ultrasound for SHM of

CompositesB. R. Tittmann1, L. P. Rojas1, A. Bhardwaj2, M. Bhardwaj2 D. Pellkofer and Y.

Trivedi1

1Penn State University, University Park, PA 168022The Ultran Group, 2380 Commercial Blvd, State College, PA 16801

Outline

1. Introduction and Background2. Gas Matrix and Piezoelectric Transducer3. Signal Processing and Simulation4. Results-Application Examples

1. Example #1 Fiber reinforced plastic FRP2. Example #2 Helicopter rotor blade3. Example #3 carbon-carbon aircraft disc brakes4. Example #4 Food Products5. Example #5 Medical

5. Conclusions

SHM and NDE with Air-coupled Ultrasound

• Advantages: • Non-contact, no-coupling material, target movement

• Approaches:1. Capacitive micromachined ultrasonic transducers (cMUTS)

(M.I. Haller; and B. T. Khuri-Yakub, 1996)2. Piezoelectric gas matrix transducers

(M. and A. Bhardwaj)

Gas-matrix piezoelectric transducer (GMPT)Active piezo-ceramic pillars are embedded in air, passive filler material of rods out of epoxy. (Gachagan et al. 1996)

Time and frequency domain of 4 MHz GMPT at 3 mm in ambient air.

• Transmission • Loss analysis

Signal processing

Simulation with Wave2000Pro to find materials for matching layers: acoustic properties of selected materials.

λ/4 matching of real materials (P*: low-density polyethylene)

Balsa Wood as Matching Layer - results of simulations using Balsa wood as matching layer material with varying thicknesses.

Example #1 Carbon fiber reinforced polymers (FRP)• Images of cured FRP

• Embedded defects• Porosity • Fiber artifacts

• Images of Pre-PregDisplacement of fibers – WavesFiber balls - Fuzzballs

CFRP composite with embedded defects (4mm thick) with line scan to the right - poor bonds attenuate signal amplitudes

CFRP composites with varying porosity (4mm thick) with line scan to the right. Increased porosity tends to attenuate ultrasound more heavily.

C-scan images of aerospace prepreg material with defects and varying resin content. The left image contains overt defects (red spots) and lower porosity (blue regions). The right image does not contain defects and is of relatively normal porosity.

C-scan image of wind turbine blade prepregmaterial with fiber misplacement (Wave Defect)

C-scan image of wind turbine prepreg with “fuzzball” ( fiber in circular ball) on left and high porosity region on right

Example #2 Rotor blade

• Rotor blades on helicopters• Difficult to inspect because of un-accessibility• Coupling via immersion or contact is difficult • Hammer-hit inspection too subjective• In-service inspection necessary

Typical External & Internal Defects

Tap-Test Hammer (Dimensions in mm)

Impact damage of composite sandwich(left)-Surface Dent(middle)-

Surface Erosion(right)

Voids in resin filler

Flaws in a layered composite -- Delamination initiation

Cross section of a helicopter rotor blade

Proposed Air-coupled inspection system

C-Scan immersion imageswith blade wrapped in plastic sheet.

Data-Gate in A-Scan with immersion

Air-coupled C-Scan of a surface impact leading to delamination

Example #3: Carbon/carbon composites

– carbon-carbon aircraft disc brakes

Impedance contrast

Material Impedance [x106 Kg ⋅m-2 ⋅ s-1]

Air 0.0004

Water 1.5

Composite Material (approximate value)

4.0

Carbon-Carbon Aircraft Disk Brakes

•Red areas=good bonding; •blue areas=disbonds between layers.

Through transmission-2D Carbon-CarbonJumbo Aircraft Disc Brakes – dark blue areas indicate poor bonding between layers

Example #4 Food Products

• Cheeses are composites of milk products and water.• hardness depends on water content• Can we measure maturity?

• Frozen meats are composites of fiber and frozen water• When partially thawed there is presence of liquid.• Can we determine degree of thawing?

Texture Analyzer TA-XT2i & Its Functional Principle

Cheese HardnessCheese Type Hardness (g)Cheddar 642Edam 753Mozarella 275Provolone 403Farmers 298Havarti 473Parmesan 687

Cheese Hardness vs. Elastic Modulus

Maturity of Cheddar Cheesevs. Acoustic Velocity

Maturity of Cheddar Cheesevs. Relative Attenuation

Received Signal for Swordfish

Calculation of Acoustic Velocity

Acoustic Velocity of Swordfish Wrapped in Plastic

Ultrasonic Signal of totally Thawed Swordfish Fillet

Acoustic Velocity of Swordfish Fillets

Relative Attenuation of Swordfish

Ultrasonic Properties of Swordfish at Distinct Temperatures

Temperature[C°]

Velocity[mm/µs]

rel. Attenuation[dB/mm]

+5 1.2376 4.96

-10 1.6501 2.75

Example #5 Medical Applications

• Contact imaging of burnt wounds are very painful• Physician needs to know depth of burn damage• Dermis damage heals quickly• Below dermis are nerves, blood vessels etc –takes special treatment• Need B-scan of burn area.

Cross-Sectional Images of Normal and Burnt Skin – pulse-echo.

Conclusions

• Air-coupled non-contact ultrasound with piezoelectric has become feasible for many applications

• The gas matrix piezoelectric transducer and advanced signal processing play key roles in the applications

• Through-transmission are routine for various composites, ranging from fiber reinforced polymers to carbon/carbon to food products to medical applications.