Ultrasonic Characterization of Porosity in Composite Laminates
Ultrasonic waves can be used as a tool to characterize the mechanical properties of materials as well as various types of defects in them. Ultrasonic characterization of the porosity (distributed minute pores) in carbon fiber reinforced composite laminates is an important issue regarding the structural integrity of composite structures. In this seminar, the basic physics of ultrasonic waves in solid media is first reviewed, and their applications to the characterization of porosity in composite laminates are discussed. Based on the recent experimental and numerical study, the influence of porosity on the ultrasonic wave velocity, wave attenuation and interlaminar interface echoes is examined. The study suggests that the irregular manufacturing conditions may lead not only to increased porosity content but also to decreased interlaminar interfacial stiffnesses of the composite laminate. By accounting for this tendency, the numerical simulations reasonably reproduce the measurements. It is also shown that while the wave velocity and attenuation can be used to characterize the average porosity content over the laminate thickness, the time-decaying features of interlaminar interface echoes can distinguish uneven porosity distributions in the thickness direction. Finally, the complexity in the ultrasonic wave propagation in curved composite laminates is demonstrated, and the feasibility of focused ultrasonic waves for characterizing porosity in such laminates is discussed.
Shiro Biwa received the degrees of Bachelor, Master and Doctor of Engineering from Kyoto University in 1990, 1992 and 1995, respectively, in major of mechanical engineering. After working in Kyoto University as a research associate during 1995-1998, he was appointed as an instructor in Nagoya University in 1998. He moved to Kyoto University as an associate professor in 2004, and has been a professor since 2009. His current appointment is in the Department of Aeronautics and Astronautics, the Graduate School of Engineering, Kyoto University. His research interests include various topics of solid mechanics, in particular, elastic wave propagation in complex media and ultrasonic methods for materials characterization and nondestructive evaluation. Currently, he is an Associate Editor of the ASME Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, and an Editorial Board Member of ZAMM (Zeitschrift für Angewandte Mathematik und Mechanik).