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Lamb Waves for Composite Health Monitoring

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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  1. Lamb Waves for Composite Health Monitoring Non-Destructive Testing – Laurens Stevaert2Ma Chemical & Materials Engineering – VUB/ULB 2012-’13

  2. Properties, (Dis)Advantages & Inspection Composites

  3. Composites: Properties • Widely used • Aerospace • Automotive • Naval • Advantages • High specific strength • Light weight • Fatigue and corrosion resistance • Design freedom – tailored properties

  4. 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!

  5. 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

  6. Properties & Application Lamb Waves

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. Weak points & Improvements Future Work

  13. 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

  14. 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!

  15. “Lamb” Wave – Vague de “Agneau”? Questions?

  16. 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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