Seminar - Nonlinear Ultrasonic Guided Waves for Early Detection of Material Degradation by Prof. Cliff J. Lissenden
Date: 20 November 2015 (Friday)
Time: 2:30 pm – 4:00 pm
Venue: EF305, The Hong Kong Polytechnic University
If detectable, incipient damage in materials provides an opportunity to predict the remaining life of a structure based on its actual condition. This knowledge enables condition-based maintenance, which in turn, would drastically reduce life cycle costs without compromising safety. Therefore, the question is ‘what technologies are capable of characterizing material degradation long before the damage reaches a critical level?’ Nonlinear acoustics is one such technology in that the wave speed depends on the displacement amplitude, thus the wave distorts as it propagates and the distortion is apparent in the frequency spectrum through the generation of higher harmonics. The special case of nonlinear ultrasonic guided waves will be discussed, due to the potential they have for efficient characterization of material degradation in plate and shell structures. As guided waves are multimodal and dispersive, the selection of wave modes and frequencies is fundamental to reliable characterization. Some key aspects of the selection process are discussed, and associated numerical and experimental results will be described.
Cliff J. Lissenden is a professor of engineering science and mechanics at Penn State. He joined the Department of Engineering Science and Mechanics in 1995 and added an appointment in Acoustics in 2011. He is an ASME fellow and was a founder of the Ben Franklin Center of Excellence in Structural Health Monitoring, which is the primary area of his research. Within SHM, his areas of specialization are guided wave ultrasonics and mechanical behaviour of materials.