Due to their high strength to weight ratio Fibre Reinforced Plastic (FRP) structures have gained their place as efficient structures for pressurised systems used in space programmes. But due to stringent weight saving measures, the FRP pressure vessels used in space programmes are designed with very low margins. Large size FRP pressure chambers are made using kevlar fibres impregnated with epoxy resin wound in hoop and polar directions in several layers. During qualification testing one of the primary failure mechanisms, namely resin crazing starts as early as 20% of the failure load. This is followed by minor delaminations, fibre pull out or disbonding between fibres and matrix. The failure is preceded by large scale delaminations and fracture of fibre bundles. Acoustic Emission (AE) technique has got proven track record in identifying the flaws, and evaluating their severity and thereby the impending failure in real time. Since the velocity of AE signal is varying from place to place in FRP pressure chambers in view of their anisotropic nature, it is difficult to locate the flaws. Hence zonal location philosophy is adopted for the AE monitoring of FRP pressure chamber testing. The paper covers the details of AE monitoring and studies done on a good number of kevlar epoxy pressure chambers during their proof pressure or burst testing as the case may be. An attempt has been made to grade the pressure chambers based on governing AE parameters like high amplitude emissions and long duration events [1] in addition to roll over of emissions during pressure holds. The percentage of high amplitude events recorded at pressure holds including that at proof pressure are taken as pointer to indicate the degradation that has taken place. The AE performance of two of the burst tested pressure chambers are taken as the basis for the grading of the chambers undergoing proof pressure testing. REFERENCE
E. V. K. Hill and T. J. Lewis, "Acoustic Emission Monitoring of a Filament Wound Composite Rocket Case During Hydro Proof Pressure Testing", Materials Evaluation, Vol. 43, pp. 859-863, 1985
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.Vol. 4, pages 2437 - 2442 Publisher:Ashgate Publishing Company
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