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Initial Investigation of Time Dependency on Failure Curvatures of FlexLam High Strain Composites



Using the column bend test (CBT) developed at Opterus R&D Inc. by Tom Murphey, effects of instantaneous and long-term bending stress rupture where investigated for the high strain composite (HSC) architecture known as FlexLam. The CBT method was selected for its ability to induce a pure moment into the test specimen while maintaining a reduced stress concentration at the clamp interface, which is critical for examining the curvature effects on these thin plate specimens at high strain states. In this investigation, two different types of tests were conducted in order to develop an understanding of the time dependent failure curvature behavior of HSC coupons. Both tests involved laminate samples with varied fiber orientations (0, 90, and +/-45 degree). The first test was to quasi-statically compress samples until failure was observed in each sample. This data was required to establish an average instantaneous failure curvature. The samples were then stowed at a constant curvature corresponding to eighty percent of the curvature observed at rupture for a long period to allow for stress relaxation within the sample. Resulting damage from the stowage was characterized into different categories based on the severity of each failure ranging from cosmetic blemishes to catastrophic failure of the laminate. Further empirical and analytical investigation of time dependent stress rupture of FlexLam HSCs will be presented in part two of this investigation.

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