题目：Fully Non-contact Systems for Damage Visualization and Diagnosis in Composite Structures
报告人：Prof. Fuh-Gwo Yuan，Professor of North Carolina State University
时间：2015年1月21日（周三）上午9:30
地点：明故宫校区9号楼506 报告厅
主办单位：国际合作交流处、科协、机械结构力学及控制国家重点实验室、航空宇航学院
报告简介：Structures fabricated with carbon fiber reinforced polymer (CFRP) composites have enjoyed wide applications, mainly due to numerous advantages over metals such as lighter weight, higher specific strength, better corrosion/chemical resistance, and etc. However, the inherently multi-layered laminate configurations are vulnerable to delamination and debonding. These failure modes can be hidden and barely visible from the surface. Such hidden flaws have also hindered the wide acceptance of using these composites for commercial applications. The nondestructive inspection (NDI) techniques become critical to determine and quantify the size, shape, and severity of the flaws.
The fully non-contact NDI techniques poses many distinct merits over any other conventional NDI techniques: (1) no sensor is needed to be either mounted onto or embedded inside the structure, which can become the weakest links in NDI system when the permanently installed sensors will be deteriorated over time; (2) the region can be arbitrarily chosen for detecting the damage as long as they are within line of sights; (3) the technique can detect incipient damage without any baseline for comparison; (4) it can scan any complex curved surfaces; (5) it can apply to structures under harsh environments such as high temperature and radioactive conditions; and (6) it can be extremely fast (in the order of thousands of measurements per second compared to the few tens of conventional technologies) and fully automated. The Integrated Structural Health Management (ISHM) Laboratory at National Institute of Aerospace has been recently focusing on developing two types of fully non-contact damage imaging systems: 1. laser-based and 2. air-coupled based.
In this talk, the two non-contact systems will be discussed and designed for automated damage visualization in composite structures respectively. The system will integrate and synchronize a Q-switched Nd:YAG laser or an air-coupled transducer for ultrasonic Lamb wave generation, a laser Doppler vibrometer (LDV) for measurement the guided waves field. A set of galvano-meters will be used to raster scan the Q-switched laser over the potential damaged area with sub-millimeter resolutions, while the LDV continuously measures the ultrasonic waves at a fixed point. The non-contact laser-based NDI system has been recently successfully developed for imaging BVID in space honeycomb structures. Using the standing wave energy approach in the frequency-wavenumber domain, the delaminated region is imaged and has agreed very well with that from X-ray CT scans. The air-coupled non-contact showed some promise for composite material characterization and damage imaging.
报告人简介：Prof. Fuh-Gwo Yuan is a professor of North Carolina State University and a Samuel P. Langley Distinguished Professor of the U.S. National Institute of Aerospace (NIA). He also served as associate director of the U.S. National Science Foundation (NSF) Center for Integration of Composites into Infrastructure (CICI). He received his Ph.D. degree from University of Illinois-Urbana-Champaign in 1986. Prof. Yuan’s main research interests include structural health monitoring, damage tolerance of composite structures, smart materials and structures, fracture and life prediction of advanced materials and structures. Currently, he is developing methods for structural diagnosis and prognosis (involving evaluating remaining life of structures using failure/statistical analysis tools). He is also developing a wireless sensor that monitors structural integrity, and methods for in-situ, mounted/embedded sensors for multi-functional composite structures. Furthermore he is studying bio-inspired morphing technologies for civil, mechanical and aerospace structures. Prof. Yuan has hosted more than 30 projects funded by NSF, NASA, U.S. ARMY, the U.S. Air Force Research Laboratory, etc.
