The Fall 2021 MatSE 590 for graduate students consists of an exciting and jam-packed schedule. MATSE 590 is a colloquium (1-3 credits) consist of a series of individual lectures by faculty, students, or outside speakers. Fall 2021 Speakers
Graduate students will receive a weekly email with information via @psu.edu email. Graduate students are required to attend all 590 Seminars. If you have any questions, please email Hayley Barnes at firstname.lastname@example.org.
*Due to the ongoing Covid Pandemic this program is being offered virtually through Zoom. Please reference the weekly email from Hayley Barnes (email@example.com) for Zoom link.
September 30, 2021
“Nonlinear ultrasonics: A cross-scale bridge between materials microstructure and macroscopic elastic properties”
Parisa Shokouhi, Associate Professor of Engineering Science and Mechanics at Penn State
Nonlinear ultrasonic testing relies on the principles of elastic wave propagation. Finite amplitude elastic waves (resulting in strains on the order of 10-6) propagating in a medium containing micro-scale features and imperfections such as grain boundaries, dislocations and micro-cracks undergo distortion, resulting in subtle but measurable changes in the response’ temporal (time domain) or spectral (frequency domain) characteristics. Measuring such changes (known as nonlinear ultrasonic parameters) makes the basis for nonlinear ultrasonic testing methods. The measured nonlinear ultrasonic parameters are directly related to the higher-order elastic constants of the medium. As a result, nonlinear ultrasonic testing provides a link between microstructure (e.g., grain size distribution and microscopic flaws) and macroscopic elastic properties of materials. The cross-scale connection between nonlinear ultrasonic parameters and performance-critical microscopic imperfections makes nonlinear UT an attractive tool for applications such as detection of ‘closed’ fatigue cracks and additively manufactured (AM) part qualification.
In this seminar, I will describe three nonlinear ultrasonic testing methods: dynamic acousto-elastic testing (DAET), nonlinear resonant ultrasound spectroscopy (NRUS) and second harmonic generation (SHG) and present some of the related work of my research group. These include: application of DAET for detection of closed fatigue cracks in aluminum, which go undetected by traditional linear ultrasonic testing; NRUS for characterizing AM samples and SHG for nondestructive evaluation of fracture toughness. Finally, I will discuss our ongoing research and some of the research needs to exploit nonlinear ultrasonics for materials characterization including developing quantitative connections between ultrasonic nonlinearity and microstructure.
Dr. Shokouhi is an Associate Professor of Engineering Science and Mechanics. Prior to coming to Penn State, Dr. Shokouhi was a research group leader in Nondestructive Testing Department of BAM - Federal Institute for Materials Research and Testing, Berlin, Germany - and a visiting Professor at Los Alamos National Laboratory (LANL). Her main research experience and expertise include: Stress wave propagation in fractured media, Nondestructive evaluation (linear and nonlinear ultrasonic testing), Structural health monitoring (acoustic emission), Machine learning and data analytics as well as Elastodynamic metamaterials. Her research projects have been supported by various programs of Department of Energy (DOE), National Science Foundation (NSF), National Institute for Standards and Technology (NIST), US Department of Transportation (USDOT) and Pennsylvania Department of Transportation (PennDOT), among others. She is a recipient of Alexander von Humboldt Fellowship, 2019 American Society of Nondestructive Testing (ASNT) Fellowship and 2020 ASNT Faculty Grant Awards. Dr. Shokouhi is the Editor-in-Chief of Research in Nondestructive Evaluation. When not working, Dr. Shokouhi enjoys spending time with her 2-year old daughter Amitis and traveling (before pandemic) as well as running and gravel/road biking in beautiful Central Pennsylvania.