| Recent decades have witnessed the rapid growth and acceptance of nondestructive evaluation (NDE) techniques in assessment of infrastructures' conditions. Assessing the conditions of infrastructures is important to determine their safety and reliability which have a great impact on today's society. The existing NDE techniques include acoustics, ultrasound, radiology, thermography, electromagnetic method, optical method, and so on. Properly employed NDE techniques can reduce the maintenance and repair cost and improve the reliability of the infrastructures.;In the last two decades, the study of the highly nonlinear solitary waves (HNSWs) has received much attention. Most of these studies focused on the propagation of HNSWs in granular systems, but little work on applications of HNSW-based NDE method has been done. HNSWs are mechanical waves that can form and travel in highly nonlinear systems, one-dimensional chain of identical spheres is one of the most common systems that can support the generation and propagation of HNSWs. In the study presented in this dissertation, a new NDE technique based on the generation and propagation of HNSWs was investigated and applied to different structural materials.;First, fundamental research on the generation of HNSWs in a chain of stainless steel beads by laser pulses was conducted. The results showed that the laser-based generation of HNSWs produces results that are equivalent to those obtained by means of a mechanical striker. Then, the feasibility of tuning HNSWs by electromagnetically induced precompression was demonstrated experimentally. By changing the precompression on the chain of particles, the properties of the HNSWs could be tuned in a wide range. Then a HNSW-based transducer was designed and built. The transducer was remotely and automatically controlled by National Instruments PXI running Labview. The ability of the new transducer to generate repeatable HNSWs was assessed. Finally, the HNSW transducer was used to monitor cement setting, concrete curing and epoxy curing, to evaluate the bond condition of an aluminum lap-joint, and to detect the impact damages in a composite plate. The results showed that the HNSW-based technique is promising for structural NDE. A pilot numerical study on acoustic lens which is a device can focus the acoustic waves at a focal point was also conducted. |
