讲座题目：报告一：Evaluation of Material Damage Using Nonlinear Acoustic Waves 
           报告二：Recent Research in SHM and NDT of Wind Turbine Blades

报告人：Dr. Jin-Yeon Kim

时 间：10月15日（周五）下午2:30
地 点：力学楼434会议室
主持人：励争（教授）

报告一内容摘要：
      Higher order harmonics are generated when ultrasonic waves propagate through a nonlinear material. One of the sources of such an acoustic nonlinearity in metallic materials is micro-structural defects such as dislocations, persistent slip bands (PSB), and precipitates that arise during fatigue, creep and other damaging processes.  Therefore, it is plausible that the magnitude of higher order harmonics may be used as a measure of damage in metallic materials.  In this talk, extensive ultrasonic measurement data using bulk, surface and Lamb waves are presented to demonstrate the correlation between the higher order harmonics and accumulative damage in different metallic materials due to monotonic loading and/or cyclic fatigue.  Other theoretical and experimental aspects of this research such as the correlation between material damage and the acoustic nonlinearity are also discussed. Finally, future research directions and unresolved important topics are briefly introduced.

报告二内容摘要：
     Wind power is a fast-growing source of non-polluting, renewable energy with tremendous potential. However, the current wind turbine technology must be improved before the potential of wind power can be fully exploited.  Wind turbine blades are one of the key components in improving this technology.  Blade failure can be very costly because it can damage other blades, the wind turbine itself, and possibly other nearby wind turbines.  A successful damage monitoring system incorporated to wind turbines may extend blade life and allow for an optimum scheduling of full-scale inspection and maintenance/ repair.  Due to their size (up to ~50 m), exposure to harsh environment, and material characteristics, the existing SHM and NDT techniques cannot be directly applied and thus need to be carefully examined and adapted for a proper operation in the actual field environment.  This talk presents recent research activities on the development of on-board monitoring and off-line inspection techniques for ensuring health of the wind turbine blade structure.  Some comparative results among different techniques are also shown.