SAMPLE TEST PROGRAMCrippling response of composite fuselage structure
In support of the NASA/Boeing ACT crown selection design validation test, Intec performed a building block program evaluating compression damage tolerance of a crown panel design.
Intec conducted tests on flat and curved, 3- and 5-stringer panels, evaluating compression damage tolerance and frame spacing effects for various material and forms. Some specimens were impacted for barely visible damage at various locations, and were then tested in compression to evaluate crippling characteristics and determine "worst case" damage locations.
 
Three-stringer panel FEM model
Additional single stringer coupons were tested to investigate skin/stringer separation, a common failure mode of post-buckled structure. Photoelasticity was used to determine full field strains around damage areas for model input.
 
Photoelastic fringe Five-stringer panel
The final building block prior to NASA's test was the compression testing of several 3 x 5 foot, 122" radius curved panels, each with three stringer elements and two circumferential frames. The panels were tow-placed with co-cured stringers and pre-cured RTM frames. An FEM model was developed to predict potential damage zone interaction and load shadowing due to end effects. Using an instrumented impactor, Intec impacted panels in the worst case locations, stringer caps and flanges.
Moiré
Intec then instrumented the panels with strain gages and crack detection wires. Some panels were instrumented with more than 140 gages. Curved panel shadow moiré for out of plane deflection was used along with high resolution video interlaced with digital strain data for real-time test monitoring. This technique allowed for post-test out of plane measurements to be taken at any load or strain level. A high speed digital sequencer was also used to determine stringer disbonding initiation and progression. Intec presented this work at the 5th Annual NASA/DOD Advanced Composite Technologies Conference.
Sample Programs
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