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Damage State Awareness in Composite Laminates Via Ultrasonic Guided Waves

Damage State Awareness in Composite Laminates Via Ultrasonic Guided Waves. Cliff Lissenden Joseph Rose Engineering Science & Mechanics The Pennsylvania State University Workshop on Prognosis of Aircraft and Space Devices, Components, and Systems Sponsored by AFOSR Cincinnati, OH

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Damage State Awareness in Composite Laminates Via Ultrasonic Guided Waves

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  1. Damage State Awareness in Composite Laminates Via Ultrasonic Guided Waves Cliff Lissenden Joseph Rose Engineering Science & Mechanics The Pennsylvania State University Workshop on Prognosis of Aircraft and Space Devices, Components, and Systems Sponsored by AFOSR Cincinnati, OH 19-20 February 2008 Impact delamination in cross-ply laminate

  2. We focus on understanding guided wave prop-agation in order to improve penetration power and sensitivity to damage. Current issues and capabilities Analysis of guided waves in composite laminates Mode excitation and tuning Synthetic reconstruction

  3. Methods for tomographic imaging of internal damage are available. Ray distributions for 16 and 8 element arrays Enable reconstruction based on signal difference, group velocity, etc. Array of PWAS Air-coupled transducer test bed

  4. Tomographic imaging enables visualization of internal damage. C-scan 16 element array 8 element array 4.23 J Impact delamination in ([0/90]s)6 CFRP with a 178 mm diametercircular array of PWAS Needs: penetration distance, number of sensors, damage sensitivity, critical size

  5. Material anisotropy results in skew angles for guided wave propagation that must be accounted for in monitoring. 300 kHz (movie) 100 mm 100 mm Unidirectional CFRP with fibers oriented at 22.5°. Wave activation is in the 0° direction. [0/45/90/-45]s CFRP laminate 200 mm x 200 mm x 1.6 mm excited by 3 cycle toneburst from 10 mm diameter PWAS

  6. Focusing of energy from a phased array can sweep through a plate. Beam control of a linear phased array for an aluminum plate, as pioneered by V. Giurgiutiu

  7. Guided wave ultrasonics can monitor structures. To be used effectively, the underlying wave mechanics must be well understood. Prognostics Signal processing Damage mechanics Etc. DAQ & analysis Angle beam Comb Natural tuning Phased array tuning Sensor design Frequency Group velocity Dispersivity Excitability Attenuation Damage sensitivity Mode & frequency selection encompasses many application specific aspects Dispersion curves and wave structure are the foundation

  8. Lamb-like and SH waves are not decoupled in anisotropic materials. Simply number modes sequentially SAFE (lines) & GMM (symbols) compare well Phase velocity dispersion curves for guided waves propagating in the 0o direction of a [(0/45/90/-45)s]2 carbon/epoxy laminate.

  9. Group velocity and attenuation dispersion curves provide valuable information for health monitoring. Kelvin-Voigt model 1 neper = 8.69 dB Group velocity dispersion curves Attenuation dispersion curves for guided waves propagating in the 0o direction of a [(0/45/90/-45)s]2 carbon/epoxy laminate.

  10. Multiple modes are often excited simultaneously. Mode 1 dominates low frequency region Natural tuning 5 cycle Hanning windowed tone burst excitation with 200 kHz central frequency – normal loading w/ 1 mm wide transducer.

  11. The source influence can be shown clearly in phase velocity-frequency space. 1D model, F(x,t) 2D Fourier Transform, F(k,w) Source Influence spectrum, F(cp,f) cp = w/f, f = w/2p 10 mm transducer, 1 MHz central freq. 10 cycle excitation, variable incidence angle, 2 mm aluminum plate

  12. The source influence is determined using the normal mode expansion (NME). Velocity field Stress field Transducer length Modes are orthogonal; v*(H) = complex conjugate of normalized velocity at top surface, T = traction vector, P = Poynting vector, x1 = prop. dir., x3 = thickness dir. Logo

  13. Guided wave A linear phased array provides mode tuning by using time delays. d Elements uniformly spaced at distance d time delays Li & Rose, 2001, IEEE Trans. 48(3):761 Logo

  14. Frequency tuning and time delays provide tremendous flexibility for mode tuning. Mode 1, cp = 1.5 km/s, Dt = 1.33 ms Dt = 1.09 ms Mode 3, cp = 6.6 km/s, Dt = 0.303 ms Dt = 0.76 ms 200 kHz central frequency 1 MHz central frequency d = 2 mm

  15. Synthetic phased array tuning provides flexibility through reconstruction. Tuned mode 1 Tuned mode 3

  16. In summary, phased array transducers can be used for synthetic focusing in composite laminates. Mode selection and tuning can improve sensitivity and penetration power Long range guided wave monitoring capabilities Questions? Logo

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