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Composite honeycomb sandwich structure is widely used for aircraft structures such as control surfaces, radomes, engine cowls, and aircraft interior structure because of its lightweight and high strength characteristics. One of the disadvantages of honeycomb sandwich structure is that they are prone to fluid intrusion. The purpose of this study is to determine if the structural properties of honeycomb core are affected by contact with a fluid. The test specimens were manufactured of fiberglass prepreg for the facesheets and Nomex® honeycomb core for the core material in accordance with ASTM C-365/365M. Test specimens were soaked in several different kinds of fluids, such as aircraft fuel, turbine engine oil, hydraulic fluid, and water for a period of 60 days. Some of specimens were tested right after soaking period ended, and some of them were dried before they were tested. A flatwise compressive test was performed, and the test results were analyzed to determine how the contact with aircraft fluids affected the compressive strength of the Nomex® honeycomb core and how the strength was recovered when the specimens were dry. In addition, the investigation of de-bonding between facesheet and core material after soaking was performed to support the study. [ABSTRACT FROM AUTHOR]

A single-ply unidirectional IM7/8552 carbon fiber reinforced plastic composite with artificially introduced circular defects is subjected to dynamic tensile loading using a modified Kolsky tension bar. A high-speed X-ray phase contrast imaging method is integrated with the Kolsky bar setup to record the crack initiation from the defects and subsequent propagation in the material in real time during the tensile loading. The tensile loading was applied either in longitudinal (0° to fibers) or transverse (90° to fibers) direction of the specimens. Shear failure of the matrix and axial splitting along the loading/fiber direction were observed in longitudinal specimens to initiate from the edge of the artificial circular defects. Debonding of fiber and matrix was observed in transverse specimens, which initiated from the top and bottom edge of the hole. The dynamic tensile loading history during the crack propagation was recorded using a piezoelectric load cell and synchronized with the observed damage and failure processes. [ABSTRACT FROM AUTHOR]