Evaluation of Innovative NDI Methods for Detection of Widespread Fatigue Damage.

High-performance high-strength aircraft components such as the FA-18 FS488 bulkhead can experience catastrophic failure in fatigue tests from very small cracks. At the same time, the efficiency of design methods used for these components results in highly uniform stressing, and a large number of fatigue cracks all growing at approximately the same rate - multi-site cracking. These circumstances place extreme demands upon the use of Non-Destructive Inspection NDI methods for finding and characterising defects, and when surface treatments such as peening are also employed to extend service fatigue life, it becomes almost impossible to detect the small crack arrays which are of concern. This report examines and evaluates some novel Non-Destructive Inspection techniques, that may allow numerous small cracks less than 1 mm over a large area to be detected. Conventional NDI techniques are also used for comparative purposes. The novel techniques used are 1 Holographic Interferometry, 2 Structural Integrity Monitor, and 3 Laser Ultrasonics. This report examines the extent to which each technique can locate cracks on a large polished specimen representing part of a bulkhead. Techniques which perform well in this evaluation will be further evaluated on a large peened specimen.