5 Composites: N-D Inspection Loads of methodsVisual inspectionOptical methodsEddy current (E-M waves)Thermography (input heat energy)Ultrasonic (high E acoustic waves)Etc.But…Cost & timeBulky transducersPart has to be removed, sometimes placed under waterPoint scan
7 Guided Wave Testing Mechanical stress waves Guided by geometry Super low freq. ( kHz)Other advantages:Elastic waves: reversible deform. mech. propertiesThrough thickness scanningImaging internal hidden defectsHigh detection range mwikipedia.org
8 Lamb Waves: Properties Discovered in 1916 but only recently appliedComplex mathematicsNeed for computational powerElastic wave in solid plates⊥ plate plane∥ propagation direction(Guided by geometry, travel long distances)Infinite number of modes, only two usedSymmetrical S0Asymmetrical A0
9 Lamb Waves: Testing Normally: transducers on the outside Good coupling required!Contact modeAir is not a good mediumImmersion in water part has to be removed…Water jets very sensitive…Non-contact modeEasier option for testingOften expensive
10 Lamb Waves: Smart Systems Small transducers permanently attachedTo the surfaceEmbedded in composite laminateConstantly monitor the structure, on demand infoPiezoelectric Wafer TransducersTransmitter: electrical E mechanical E (elastic waves)Receiver: mechanical E (propagated wave) electrical EE.g.: PZT – Lead Zirconate Titanateeetimes.com
11 Lamb Waves: AnalysisDifferent ways to analyze signal – depends on applicationExamplesTOF measurement: defect locationDefect ≈ material with different prop.Wave: different velocity (slower)Comparison of wave peak locationsLaser vibrometer: defect locationNon-contact vibration measurement: Doppler shift of laser frequency due to surface vibration3D lamb wave, follow peak-to-peak amplitudesFinite element-based technique: defect sizeMeasure reflection and transmission coefficientsPredict these coefficients for set of damage parametersParameter optimization defect geometry
13 Future Work Commercial applications limited… for now Some disadvantagesSingle mode: dispersion properties needed difficult for composites!Low frequency = large wavelengths small defects not correctly measuredAnalysis over long time influenced by T, loading, bad coupling…Anisotropy Commercial applications limited… for now
14 Conclusion Promising technique! Lamb waves Smart systems Special propertiesPropagate through plate geometriesDetection over large distancesSmart systemsActive structural health monitoringMonitor damage (evolution)While in-service! Promising technique!
16 SourcesDiamanti, K. et al (2010) Structural Health Monitoring Techniques for Aircraft Composite Structures. Progress in Aerospace Sciences, Vol 46, pp. 342 – 352Staszewski, W.J. et al (2008) Health Monitoring of Aerospace Composite Structures – Active and Passive Approach. Composites Science and Technology, Vol 69, pp – 1685Castaings, M. et al (2011) Sizing of Impact Damages in Composite Materials Using Ultrasonic Guided Waves. NDT&E International, Vol 46, pp. 22 – 31
Your consent to our cookies if you continue to use this website.