(From LI Changzheng of Ultrasonic Physics and Exploration Laboratory)Dr. John H. Cantrell, a Senior Material Physicist of NASA, was invited by Research Department and Ultrasonic Physics and Exploration Laboratory to give an academic report on October 11, 2010. The title is "Fatigue damage accumulation and acoustic nonlinearity in metals".
Dr. John H. Cantrell graduated from University of Tennessee with PhD in physics in 1976. Now he is a Senior Materials Physicist in Research and Technology Directorate of Nondestructive Evaluation Sciences Branch, NASA Langley Research Center. He is well up in Materials Physical field due to his abundance of speculative knowledge and practical experiences. His achievements on material structure-physical property relationships led to a number of scientific awards. He is a Fellow of the American Physical Society, Fellow and Chartered Physicist of the Institute of Physics (London), and Fellow of the Acoustical Society of America. Up to now, he published 167 articles and was granted 26 U.S. patents.
In the report, based on the developing history of harmonic generation in the material fatigue research field, Dr. John H. Cantrell firstly introduced most significant findings of bulk wave studies, nonlinear wave equations and the appliance of nonlinear parameters. Then he provided the theoretical plots of nonlinearity parameter versus stress amplitude for several kinds of metals and curves of nonlinearity parameter versus percent fatigue life for aluminum alloy. He gave an inspecting example of a steam turbine and analyzed the nonlinear harmonic inspecting results. Finally, Dr. John H. Cantrell expected to develop physics-based model of nonlinear interactions of acoustic waves with fatigue-generated substructures that evolve during fatigue process, and study reliable fatigue monitoring system on harmonic generation utilizing comparison method between model predictions and experimental measurements.
Focusing on some hot spots on material inspection, the researchers of Ultrasonic Physics and Exploration Laboratory took lively discussion with Dr. John H. Cantrell. Participants thought they had obtained much knowledge in the fields of fatigue material and nonlinear inspection, especially in the realm of nondestructive assessment and development overseas.
