CompositesWorld
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47 CompositesWorld.com NEWS N E W S N S N E W S E N W S W SHM Update SIDE STORY Although CW's coverage of structural health monitoring (SHM) technologies in this issue focuses on those most actively employed in testing/ demonstration environments and most ready for widespread deployment, there are a broad range of SHM types that take advantage of a variety of sensing mechanisms. The following is a short sketch of each, accompanied by two tables that indicate current uses and developmental progress. Acoustic Emission (AE): Passive transducers listen for matrix cracking, delamination and fber breakage. Acousto-ultrasonics (AU): A grid of piezoelectric sensors sends and receives ultrasonic pulses and analyzes changes in wave patterns to identify and describe damage. Comparative Vacuum Monitoring (CVM): The smallest air fow can be detected when galleries alternating between atmospheric pressure and vacuum (enabled by Tefon manifold patch) are breached by a crack or resin microcracks. CVM Through the Thickness (CVM-TT): A <1 mm- diameter hole drilled through a composite into adhesive uses the CVM principle to detect disbond and delamination. Crack Wire (CW): Conductive/resistance wires that trigger alarms when severed by cracks or damage. Electro-Magnetic Interference (EMI): Uses embedded piezoelectric sensors and impedance analyzer. Increasing levels of internal release agent and moisture contamination, for example, produce increasing devia- tion from a reference index, indicating weak bonds. Eddy Current Foil Testing Sensors (ETFS): Sensors generate an eddy-current feld in conductive metals, which is disrupted by cracks and corrosion. Fiber Bragg Grating (FBG): A mature type of Fiber Optic Sensing (FOS), it uses alterations in the refractive index of an optical fber to measure temperature, strain and vibration as well as acoustic and ultrasonic signals for crack and damage monitoring. Impact Damage Detection System (IDDS): Developed by Kawasaki Heavy Industries, this system uses two combined methods: (1) optical intensity measurement before and after impact, using optical fbers to assess damage and (2) shock wave measurement for impact localization via FBG sensors. Imaging Ultrasonics (IU) — Miniaturized, integrated sensor networks generate a signal through the material. Changes in wave refection indicate faws or damage. Strain Gauges (SG) — These output strain, stress and load, using traditional electrical foil sensors and an input voltage. Newer sensor types include fber-optics, microelectromechanical systems (MEMS) and printed conductive-ink sensors. The Structural health monitoring toolbox TABLE 1 SHM TECHNOLOGIES Generic Use Case CVM ETFS AE IU CW IDDS AU FOS EMI CVM- TT SG Crack detection and assessment X X X Rupture detec- tion of structures X X X Impact detection and assessment X X X Delamination detection and assessment X X X X X Bond quality assessment X X X X Bonded repair monitoring X X X Debonding detection and assessment X X X Stress/strain monitoring X X TABLE 2 SHM TECHNOLOGY TESTING (not exhaustive) SHM Suppliers Demonstration Projects In-service Monitoring of Certifcation Tests Protosystems Flying on Aircraft AE Physical Acoustics Corp (PAC, Princeton Junction, NJ, US) • B777 horizontal stabilizer full-scale fatigue and ultimate load tests • A380 full-scale fatigue test Airborne Acoustic Integrity Monitoring System (AAIMS) on U.S Navy P-3 Orion feet ** AU Acellent Technologies (Sunnyvale, CA, US) SMART Layers • Embraer in-fight tests at airlines • H-60 helicopter fight tests • A350 door surround impact detection - ground and fight validators Learjet 85 fight test monitor impact damage to composite vertical stabilizer (tail) CVM Structural Moni- toring Systems (Nedlands, Australia; Ashford, UK and Century City, CA, US) • Embraer in-fight tests at airlines • Delta Air Lines/Sandia program testing seven Boeing 737 aircraft in service A380 full-scale fatigue test CW A380 full-scale fatigue test Tail strike indica- tion (TSI) system on A340-500/600 and A380 FBG JASTAC I and II A350 horizontal tail plane (HTP) structure & fight testing SG A400M Life-Time Monitoring System (LTMS) ** Supplier for AE sensors used in AAIMS is not known. Boldface "X" indicates proven high performance in that area.