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Structural Health Monitoring (SHM)

Structural Health Monitoring (SHM). By Kevin Wynter. Outline. SHM Basics Invasive Methods Non-Invasive Methods Experimental Methods. SHM Basics. What is SHM?

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Structural Health Monitoring (SHM)

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  1. Structural Health Monitoring (SHM) By Kevin Wynter

  2. Outline • SHM Basics • Invasive Methods • Non-Invasive Methods • Experimental Methods

  3. SHM Basics What is SHM? • Structural Health Monitoring, is an approach used for damage detection and behavioral characterization of structures, in order to evaluate performance • Can be large scale (bridge) or small scale (helmet) • Long-term analysis (material creep effects) • Short-term analysis (impulse testing) • Think of SHM systems as complex transducers: physical properties optical/electrical/acoustic response (stress, strain, resistivity)

  4. SHM Basics Statistical Pattern Recognition Paradigm [1] • Operational Evaluation • Data Acquisition • Extraction and Data Compression • Modeling for Feature Discrimination SHM System • Structure • Sensors • Data acquisition/transfer/management system • Data processing and interpolation software

  5. SHM Basics Examples • Huey P. Long Bridge, Louisiana • More than 800 sensors • Axial and bending • Comanche Helicopter • Active rotor system • Our of plane loading effects

  6. Invasive Methods Strain Gauges • Surface mounted electromechanical sensors • Measures the state of strain in an object • Correlates the mechanical deformation of structure to resistance of the coil by the gauge factor • Wheatstone bridge design • Extensive surface preparation required

  7. Invasive Methods Destructive Methods • Enveloping, cutting or otherwise permanently changing physical state • Decommissioning • Combines with some other technique (strain gauge, optical, ultrasound etc.) • Usually performed according to cyclic schedule or specific event • Structure is rendered inoperable – tested to failure

  8. Non-Invasive Methods Carbon Nanotube (CNT) • Main idea is to integrate thread directly into the fibers of the composite. • CNT thread was chosen due to its highly favorable electrical and mechanical properties • Fibers are small in size (10-30 µm in diameter) [1] allowing them to be integrated into the structure without compromising reliability • Can be implemented as one sensory circuit, and provide real time monitoring of the structural health of a component CNT thread being pulled from the forest b) Close up of thread c) Two threads in twist d) CNT ribbon [2] Two-thread yarn. [2]

  9. Non-Invasive Methods Electronic Speckle Pattern Interferometry (ESPI)[3] • Optical method using lasers and sophisticated cameras to detect subtle changes in a surface • Surfaces must be non-uniform • Laser reflects off of surface, and the interference of multiple light fields create a speckle image representing the surface • Surface will appear the same if the phase difference of the light fields is an integer multiple of 2π

  10. Non-Invasive Methods Digital Image Correlation (DIC)[4] • Optical method similar to ESPI which tracks small changes in an object associated with deformation • Surface is prepared with optical element, and cameras are used to associate each point on the surface with a reference coordinate • A stochastic intensity pattern on the surface is used to create 3D and 2D imaging of the property being analyzed by way of a correlation algorithm

  11. Non-Invasive Methods Ultrasonic Scan (UT)[5] • Acoustic method in which an object is submerged and using pulses, internal characteristics of the object are examined • Frequency used is typically <1 - 50 MHz • Comprised of a pulser/receiver, transducer and display devices • Very useful for complex structures and detection of small flaws and changes • A direct image of subsurface and its properties can be obtained

  12. Experimental Methods 3D Technology Acoustic Signatures

  13. Questions? ???

  14. Sources [1] Farrar, C. R.; S. W. Doebling and D. A. Nix (2001). "Vibration-Based Structural Damage Identification". Philosophical Transactions of the Royal Society: Mathematical, Physical & Engineering Sciences 359 (1778): 131–149. doi:10.1098/rsta.2000.0717. [2] Edge Delamination in Angle-Ply Composite Laminates S. S. Wang. 1984. [3] Jones R & Wykes C, Holographic and Speckle Interferometry, 1989, Cambridge University Press [4] http://www.dantecdynamics.com/Default.aspx?ID=1030 [5] http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/Introduction/description.htm

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