Failure analyses of polymer matrix composite (PMC) honeycomb sandwich joint panels

The objective of this thesis is to investigate the structural behavior and material failure characteristics of polymer-matrix composite (PMC) honeycomb sandwich joint panels under several transverse loads which resulted in web bending as typically experienced by aircraft wing skin. Several PMC honeycomb sandwich joint panels were fabricated as part of the demonstration test elements to provide structural concepts for the High-Speed Civil Transport (HSCT) wing. Test elements were preliminarily designed and sized under design-integration trade studies (DITS) task. Test elements selected for this study included 2 PMC honeycomb sandwich joint panels; 1 panel consisted of a honeycomb sandwich wing skin bolted joint by 2 fiber-reinforced composite spar caps to a honeycomb sandwich spar web; the other panel had the same structural concept except that the composite spar caps were replaced by the titanium ones. Essential components in the sandwich construction were composite face sheets, honeycomb cores, and core-to-facing bonding material.; Subsequently, these test elements were statically loaded to failure in room temperature at NASA Langley Research Center. The test was designed to simulate flight load condition of 15 psi fuel over pressurization against the wing spar during supersonic maneuver. The experimental results were compared via finite element analyses and failure predictions. Geometric linear and non-linear finite element models were constructed to simulate the failure behaviors of these test panels. Failure theories such as the Yeh-Stratton, Tsai-Wu, Tsai-Hill, and maximum stress and strain criteria were utilized to check the experimental results and predict the failures. The basis for calculating the composite failure was the first-ply failure method. Based on the evaluation of these test elements by comparing experimental failures to finite element analysis results, the test element attached by 2 titanium spar caps was structurally superior to the other test element attached by composite spar caps. Therefore, the test element attached by 2 titanium spar caps was down-selected for the upcoming subcomponent qualification test.