Detection and Characterization of Imperfections in Composite Pressure Vessels

Interpreting the information given in a thermogram can be a difficult task under ideal circumstances and extremely challenging in a real world setting. The work discussed in this paper illustrates how the microstructure of several commonly found defects in composite structures relate to their thermographie image counterpart. Two test cases are studied herein, including a large graphite/epoxy RP-1 fuel tank and a graphite composite cryogenic fuel feedline. The structures used in this study were designed to serve as manufacturing proof of concept specimens and to undergo hydroburst testing to verify manufacturing practices and structural design. Prior to hydrostatic testing the structures underwent 100% thermographic evaluation to ensure that no manufacturing or handling damage was present. Due to a large inclusion found in the feedline, it was pulled from service and dissected without performing the hydroproof. The thermographie indications found in the RP-1 tank were below critical limits so it underwent a complete hydroproof loading series and finally a hydroburst. Following the hydroburst samples were cut from the tank in regions where thermography had located damage before the test. These regions were re-evaluated thermographically and then were cross-sectioned and photomicrographed.