One example of rod-reinforced advanced composite structures is the rodpack hat stringer developed for tiltrotor wing applications. Previous rodpack hat stringer compression tests indicated that the initial failure mode involves the skin buckling away from the hat. A possible source of this buckling instability is a delamination growing from the free edge of the flange. Hat stringer pull-off tests were performed to evaluate the delamination failure mechanisms in the flange region for a rod-reinforced hat stringer section. A special test fixture was used to pull the hat off the stringer while reacting the pull-off load through roller supports at both stringer flanges. Microscopic examinations of the failed specimens revealed that failure occurred at the ply termination in the flange area where the flange of the stiffener is built up by adding 45/-45 tape plies on the top surface. Test results indicated that the as-manufactured microstructure in the flange region has a strong influence on the delamination initiation and the associated pull-off loads. Finite element models were created for each specimen with a detailed mesh based on micrographs of the critical location. A fracture machanics approach and a mixed mode delamination criterion were used to predict the onset of delamination and the pull-off load. By modeling the critical local details od each specimen from micrographs, the model was able to accurately predict the hat stringer pull-off loads and replicate the variability in the test results.
Test and analysis of composite hat stringer pull-off test specimens
Test und Analyse von Verbundträger-Zugproben
Journal of the American Helicopter Society ; 42 , 4 ; 350-357
1997
8 Seiten, 17 Bilder, 1 Tabelle, 10 Quellen
Aufsatz (Zeitschrift)
Englisch
Test and Analysis of Composite Hat Stringer Pull-off Test Specimens
Online Contents | 1997
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