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Lamb Waves for Composite Health Monitoring

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Presentation on theme: "Lamb Waves for Composite Health Monitoring"— Presentation transcript:

1 Lamb Waves for Composite Health Monitoring
Non-Destructive Testing – Laurens Stevaert 2Ma Chemical & Materials Engineering – VUB/ULB 2012-’13

2 Properties, (Dis)Advantages & Inspection

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. ( kHz) Other advantages: Elastic waves: reversible deform.  mech. properties Through thickness scanning Imaging internal hidden defects High detection range m

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

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  Commercial applications limited… for now
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  Promising technique! Lamb waves Smart systems
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”?

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 – 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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