EXTENDED FATIGUE TESTING OF HIGH-USAGE AIRCRAFT FUSELAGE STRUCTURE

Teardown inspections and extended fatigue testing are an effective means to determine the structural integrity of high-time, high-usage aircraft. The Federal Aviation Administration (FAA), Delta Air Lines, and Drexel University teamed to perform teardown inspection and extended fatigue testing of a retired B727 aircraft near its design service goal of 60,000 flight cycles. Eleven fuselage panels were removed from the aircraft. In seven panels, the state of multiple-site damage (MSD) is characterized through nondestructive inspections (NDI) and fractographic examinations. For the remaining four panels, the state of MSD will be advanced through extended fatigue testing using the FAA’s Full-Scale Aircraft Structural Test Evaluation and Research facility and continuously assessed through both conventional and emerging NDI methods. This paper reports the results of extended fatigue testing of the first of four panels. The test panel was instrumented with strain gages, and quasi-static tests were conducted to ensure a proper load introduction into the panel. Crack formation during fatigue testing was monitored in realtime using high-magnification visual inspections and conventional and emerging NDI methods. To support these tests, geometric nonlinear shell analyses were conducted using the finite element method to predict the strain distributions and other parameters governing crack initiation. No cracks were detected in the panel skin test section after an additional 43,500 simulated flight cycles. The test was terminated due to extensive cracking in the load attachment points of the panel outside the test section. A posttest destructive evaluation is underway to determine if nondetectable cracks developed.