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Description:
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In the design of cryogenic fuel tanks for the next generation Reusable Launch Vehicles (RLVs ) , the permeability of liquid hydrogen (LH2 ) across the thickness of the tank is a critical issue . The rate of permeation of LH2 is largely dependent on the internal damage state of the composite tank wall . Damage in the form of matrix cracks in the composite material of the tank is responsible for the through -the -thickness permeation of LH2 . In this context , the detection of matrix cracks takes on an unprecedented significance . In this work , an ultrasonic technique for the ply -by -ply detection of matrix cracks in laminated composites is developed . Experimental results are presented for graphite /epoxy laminates with different lay -ups and laminate thicknesses . Matrix cracks in each of the plies of the laminated composites were detected even when there was a rather high density of cracks in all of the plies . The ultrasonic data were calibrated by comparing them with the corresponding results obtained by using the traditional methods of optical microscopy and penetrant enhanced X -radiography . Excellent quantitative correlation was observed between the results obtained with ultrasonics and the traditional methods . |