Multi-Component Structural Health Assessment Using Guided Acoustic Waves

Abstract

In this dissertation different structural materials (aluminum and steel) with different geometrical shapes (plates, pipes and bars) are studied for damage detection with guided waves. Specific guided wave modes (also known as Lamb wave modes for plate type structures) are generated in a laminated aluminum plate for damage detection and quantification using a broad band piezoelectric transducer structured with a rigid electrode. Appropriate excitation frequencies and modes for inspection are selected from theoretical and experimental dispersion curves. Sensitivity of anti-symmetric and symmetric modes for delamination detection and quantification is investigated. Longitudinal guided waves are excited and recorded after transmission through reinforcing steel bars for monitoring its corrosion level. Instead of investigating the amplitude of the transmitted guided waves, or in other words, monitoring its attenuation, the differential time-of-flight (TOF) is recorded. A reliable guided wave mode is identified for the detection and quantification of corrosion in reinforcing steel bars. Hole type damage, and bonding/de-bonding or lamination/delamination in pipes are studied with Noncontact Electro-Magnetic Acoustic Transducers and PZT transducers. An adaptive method using phase of the recorded signals for detection and quantification of damages in pipes is established using multiple feature extraction techniques (Time-Frequency representations) and differential time-of-flight cross-correlation technique.