ABSTRACT
Nondestructive testing (NDT) and nondestructive evaluation (NDE) methods are used throughout the life of materials and structures from the initial steps of fabrication and throughout the operating life of the structures in service [Bar-Cohen, 2000]. Such methods are applied to inspect materials, parts, safety-critical components, structures, and systems. Similar methods are even used to perform diagnosis of our body and are also applied throughout the world to detect concealed weapons and explosives on passengers in airports. Generally, NDE methods require removal of the test articles from service; the structure is scanned to detect the presence of ¤aws as well as determine the material properties. To test structures while they are in service, structural health monitoring (SHM) methods are used where sensors are employed to detect defects that are forming. Flaws that may
CONTENTS
5.1 Introduction .......................................................................................................................... 79 5.1.1 NDE and NDT Methods .........................................................................................80 5.1.2 Structural Health Monitoring ................................................................................80 5.1.3 Electromagnetic Acoustic Transduction ............................................................... 81
5.2 Cryogenic NDT and Transition Detection Methods ...................................................... 82 5.2.1 EMAT Test of Transonic Wind Tunnel Turbine Blades ......................................84 5.2.2 EMAT Test of North American Eagle F-104 Fighter Jet ...................................... 89 5.2.3 Signal-to-Noise Reduction of Low Temperature Eddy-Current NDE ............. 96
5.2.3.1 The Material Parameters That Affect Eddy-Current Measurements ....96 5.2.3.2 Maximizing the Signal-to-Noise Ratio at Cryogenic Temperatures ......97 5.2.3.3 NDT of the Cryogenic Processing Effects on Structure-Critical
Fasteners ..................................................................................................... 97 5.3 Low Temperature NDE Case Study ................................................................................ 101
5.3.1 Problem Description .............................................................................................. 102 5.3.1.1 NDE Limitations ..................................................................................... 102 5.3.1.2 The Developed Test Method .................................................................. 103
5.4 Conclusions ........................................................................................................................... 106 Acknowledgments ...................................................................................................................... 106 References ..................................................................................................................................... 107 Internet Reference ....................................................................................................................... 107
emerge in service include corrosion and fatigue cracks. The use of SHM methods allows extending the life of structures and safely operating them, since they are monitored while they are aging and they are removed from service only if a cause for concern is identi†ed. The NDE methods that are generally used include ultrasonics, visual, infrared, thermal, electrical, electromagnetic and eddy current, radiographic, microwave, and spectroscopy. The SHM methods that are used rely on the availability of sensor technologies that are applicable to the operating conditions of the speci†c materials and structures as well as the required information that needs to be determined. The application of NDE and SHM methods at low temperatures is mostly done at the lab and under outdoor conditions in the †eld, including aircraft structures that are operated under cold conditions, as well as drilling facilities and pipelines in such cold places as Alaska in the winter.
