Lamb waves for composite health monitoring
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Lamb Waves for Composite Health Monitoring. Non-Destructive Testing – Laurens Stevaert 2Ma Chemical & Materials Engineering – VUB/ULB 2012-’13. Properties, (Dis)Advantages & Inspection. Composites. Composites: Properties. Widely used Aerospace Automotive Naval Advantages

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Lamb Waves for Composite Health Monitoring

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Lamb waves for composite health monitoring

Lamb Waves for Composite Health Monitoring

Non-Destructive Testing – Laurens Stevaert2Ma Chemical & Materials Engineering – VUB/ULB 2012-’13


Composites

Properties, (Dis)Advantages & Inspection

Composites


Composites properties

Composites: Properties

  • Widely used

    • Aerospace

    • Automotive

    • Naval

  • Advantages

    • High specific strength

    • Light weight

    • Fatigue and corrosion resistance

    • Design freedom – tailored properties


Composites properties1

Composites: Properties

  • Disadvantage: impact damage

    • Low through-thickness strength

    • Even low velocity!

    • Bird strike

    • Tool dropped during servicing

    • Runway stones

  • Damage

    • Indentation

    • Delamination

    • Fibre/matrix cracking

    • “Barely Visible Impact Damage”

 Detect, locate & characterize damage!


Composites n d inspection

Composites: N-D Inspection

  • Loads of methods

    • Visual inspection

    • Optical methods

    • Eddy current (E-M waves)

    • Thermography (input heat energy)

    • Ultrasonic (high E acoustic waves)

    • Etc.

  • But…

    • Cost & time

    • Bulky transducers

    • Part has to be removed, sometimes placed under water

    • Point scan


Lamb waves

Properties & Application

Lamb Waves


Guided wave testing

Guided Wave Testing

  • Mechanical stress waves

  • Guided by geometry

  • Super low freq. (10-100 kHz)

  • Other advantages:

    • Elastic waves: reversible deform.  mech. properties

    • Through thickness scanning

    • Imaging internal hidden defects

High detection range 100m

wikipedia.org


Lamb waves properties

Lamb Waves: Properties

  • Discovered in 1916 but only recently applied

    • Complex mathematics

    • Need for computational power

  • Elastic wave in solid plates

    • plate plane

    • propagation direction

    • (Guided by geometry, travel long distances)

  • Infinite number of modes, only two used

    • Symmetrical S0

    • Asymmetrical A0


Lamb waves testing

Lamb Waves: Testing

  • Normally: transducers on the outside

  • Good coupling required!

  • Contact mode

    • Air is not a good medium

    • Immersion in water  part has to be removed…

    • Water jets  very sensitive…

  • Non-contact mode

    • Easier option for testing

    • Often expensive


Lamb waves smart systems

Lamb Waves: Smart Systems

  • Small transducers permanently attached

    • To the surface

    • Embedded in composite laminate

    • Constantly monitor the structure, on demand info

  • Piezoelectric Wafer Transducers

    • Transmitter: electrical E  mechanical E (elastic waves)

    • Receiver: mechanical E (propagated wave)  electrical E

    • E.g.: PZT – Lead Zirconate Titanate

eetimes.com


Lamb waves analysis

Lamb Waves: Analysis

  • Different ways to analyze signal – depends on application

  • Examples

    • TOF measurement: defect location

      • Defect material with different prop.

      • Wave: different velocity (slower)

      • Comparison of wave peak locations

    • Laser vibrometer: defect location

      • Non-contact vibration measurement: Doppler shift of laser frequency due to surface vibration

      • 3D lamb wave, follow peak-to-peak amplitudes

    • Finite element-based technique: defect size

      • Measure reflection and transmission coefficients

      • Predict these coefficients for set of damage parameters

      • Parameter optimization  defect geometry


Future work

Weak points & Improvements

Future Work


Future work1

Future Work

  • Some disadvantages

    • Single mode: dispersion properties needed  difficult for composites!

    • Low frequency = large wavelengths  small defects not correctly measured

    • Analysis over long time influenced by T, loading, bad coupling…

    • Anisotropy

 Commercial applications limited… for now


Conclusion

Conclusion

  • Lamb waves

    • Special properties

    • Propagate through plate geometries

    • Detection over large distances

  • Smart systems

    • Active structural health monitoring

    • Monitor damage (evolution)

    • While in-service!

 Promising technique!


Questions

“Lamb” Wave – Vague de “Agneau”?

Questions?


Sources

Sources

  • Diamanti, K. et al (2010) Structural Health Monitoring Techniques for Aircraft Composite Structures. Progress in Aerospace Sciences, Vol 46, pp. 342 – 352

  • Staszewski, W.J. et al (2008) Health Monitoring of Aerospace Composite Structures – Active and Passive Approach. Composites Science and Technology, Vol 69, pp. 1678 – 1685

  • Castaings, M. et al (2011) Sizing of Impact Damages in Composite Materials Using Ultrasonic Guided Waves. NDT&E International, Vol 46, pp. 22 – 31


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