Fluid-ingression phenomena in composite sandwich structures is a concern for componentsemployed in the aerospace industry. Poor design/material selections, impact damages, thermomechanicalloads occurring during ground-air-ground (GAG) cycling and changes to internalpressure within the sandwich structure all lead to localized transverse cracks, delaminations,facesheet/core disbonds and core damages which create more passageways for fluid migration. Insome cases, damage growth due to latter two cases is stable and occurs over a period of flights,but may not be readily detected on the ground when the thermo-mechanical and internal pressureloads are released. Hence, the structure will continue to sustain load-carrying capabilities until thedamage size reaches a critical damage threshold (CDT) which leads to catastrophic failure. Unlesssuch damage is detected and repaired prior to reaching CDT, GAG effects will further increase thedamage size and threaten the structural integrity and safety of the aircraft. Current researchprovides an analytical method to predict facesheet debond based on the Winkler foundationapproach that agrees well with both numerical and experimental results and evaluates thecapabilities of cohesive zone modeling to predict onset of damage growth. Also, a standardizedprocedure and test apparatus for GAG testing to simulate damage under a mixed-mode stress statecaused by the pressure differential and in-plane mechanical loads is developed. Current phase ofthe research focusses on investigating the effects of GAG cycling on sandwich structures bysubjecting them to combined pressure and in-plane mechanical loads and investigate the conditionsleading to the onset of damage, and to develop a method to conduct GAG simulation based onSCB model calibration. The information gathered through this research will be instrumental indeveloping analytical methods and validating finite element analysis procedures to furtherinvestigate the damage growth mechanics of sandwich composite structures.
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