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Fatigue Technology Inc. performed extensive fatigue testing using the specimen configuration shown in Figure 1 to determine the likely fatigue life improvement factor associated with the TCTO-2060 repair concept. Specifically, baseline specimens were run, and repaired specimens were cycled to failure. Failure was defined as a crack growing into the thickness-change radius. The results of each of the test specimens are included in Table 1 and graphed in Figure 2.

FIGURE 1

The test data indicates that the ForceTec repair will greatly increase the life of the joint at access panel location #3421. This data should only be used for trends and not for actual life expectancy comparisons.

Life to crack detection

The fatigue life of the specimens can be compared to time to first crack observation. The initial cracks were typically found when they were very small (less than 0.010-inch) except on F16HPFTCX6 (first observation at 0.022-inch). In the baseline specimen (F16HPBASE2) the first crack initiated from a fastener hole. In the specimens prepared with FtCx retainers, the initial crack started from the edge of the cut-out. The time to first observation was a minimum of 2.8 times later for the reworked specimens than for the baseline specimen.

Life to specimen failure

The end of test was determined as a crack that exceeded the length of the land (web) area and was visible outside the door area on the front of the specimen (approximately 1.1 inches long). This size of crack could cause "functional impairment" (a fuel leak on the aircraft). The rework specimens had cracks located away from the test area, typically on the specimen at a stiffener attachment fastener, start before land failure occurred. In these specimens the end of test point is conservative for the comparison to web failure with the baseline specimen. The minimum time to land failure of a specimen prepared with FtCx retainers was 3.1 times that of the baseline specimen.

Test Summary with Maximum Spectrum Load at 46.78 kip

Summary