Date of Award
Master of Science
Air-coupled ultrasound is a non-contact technique and has clear advantages over water-coupled testing. This work aims at gaining quantitative understanding of the principles underlining air-coupled ultrasonic measurement. The beams of air transducers, with and without Apodization, were mapped out. The transmission of air-coupled ultrasonic energy through a plate is measured experimentally; model calculation of the transmission coefficient, taking into account the real transducer characteristics, is compared with the experimental results. The occurrence of "Poisson bright spot" in the flaw images of thin laminates and honeycomb composites were investigated; A qualitative comparison with a model based on the Fresnel's wave theory of light is discussed. Through transmission C-scans at 120 and 400 kHz using focused transmitter and receiver were studied; Apodization of the transducers and its effects on the resolution were studied. In addition to the two-sided through transmission mode, the air-coupled ultrasound system was used to launch and receive Lamb waves. Conical attachments were added to reduce the unwanted "cross-talk". The detection sensitivity of disbonds under thick-facesheet using air-coupled Lamb waves was investigated in a set of honeycomb sandwiches with 3-ply to 15-ply facesheets. Furthermore, Air-coupled scan results will be discussed for a variety of composite materials and structures, from thin laminates and honeycomb composites to thick composite rocket casing; [This work was supported by the NSF Industry /University Cooperative Research Center for Nondestructive Evaluation at Iowa State University.]
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
Vashmi Krishna Reddy Kommareddy
Kommareddy, Vamshi K.R., "Air-coupled ultrasonic measurements in composites" (2003). Retrospective Theses and Dissertations. 236.