| This research investigates the use of Rayleigh waves for the identification of near surface fractures in structural elements. The study involves a conceptual analysis, finite element modeling and small scale experimentation. Initial work on thin Plexiglas sheets develops the methodology of Rayleigh wave measurement and examines the interaction of a Rayleigh wave with a slot Subsequent finite element modeling further advances the understanding of the Rayleigh wave/fracture interaction. The final step uses the methodology and knowledge gained from Plexiglas plates to study the ability of Rayleigh waves to detect slots in small scale concrete beams.;To begin, the study focuses on the characteristics of a Rayleigh wave formed in an infinite half-space. A subsequent chapter introduces the signal processing techniques and algorithms used to measure Rayleigh wave dispersion and energy density in the frequency-wavenumber (FK) domain. Experimental measurements on two-dimensional Plexiglas analogues define the appropriate test procedures and interpretation criteria needed for the characterization of Rayleigh waves.;Finite element modeling provides additional knowledge about the Rayleigh wave/fracture interaction. Initially, the finite element model is calibrated using experimental data and material parameters quoted in the literature. Subsequent simulations study time-acceleration measurements made at different locations inside the plate for various slot depths.;A series of experiments further examines the slot detection ability of Rayleigh waves in small concrete and cement beams. Initial measurements provide insight into Rayleigh wave motion at different locations on the beam. A finite element model calculates theoretical dispersion curves for comparison with experimental results. In addition, the finite element model illustrates that Rayleigh waves form by the superposition of fundamental flexural and longitudinal modes at high frequencies and wavenumbers.;This method would benefit by additional work examining different receiver arrangements and frequency regulated input sources. Also, further theoretical and experimental work should focus on combining the knowledge acquired from Rayleigh waves with information gained from observed higher vibrational modes. (Abstract shortened by UMI.). |
