The spacecraft components viz., central cylinder, deck plates, solar panel substrates, antenna reflectors are made of aluminium / composite honeycomb sandwich construction. Detection of these defects spacecraft structural components is important to assess the integrity of the spacecraft structure . Electronic Speckle Interferometry (ESI) techniques identify the defects as anomalous regions in the interferometric fringe patterns of the specklegram while the component is suitably stressed to give rise to differential displacement / strain around the defective region. Calibration studies, different phase shifting methods associated with ESI and the development of a prototype Twin Head ESSI System ( THESSIS) and its use for the NDE of a typical satellite structural component are presented.
1.INTRODUCTIONThe spacecraft components viz., central cylinder, deck plates, solar panel substrates, antenna reflectors are made of aluminium / composite honeycomb sandwich construction. Also the thin walled propellant tanks of the spacecraft are made of titanium alloy. Defects in these components can severely limit the performance and in some cases cause the failure. Defects like debonds in honeycomb sandwich components are likely to occur either during fabrication process or testing. and crack like defects in the thin walls of the propellant tanks. Detection of these defects spacecraft structural components is important to assess the integrity of the spacecraft structure. Holographic and Electronic Speckle Interferometric techniques, because of their high displacement sensitivity( /2 = 0.3 m), whole-field and non-contact nature are found to be very useful for Non-Destructive Evaluation (NDE) of these spacecraft structural components [1][2][3][4][5]. The defects are identified as anomalous regions in the interference fringe patterns of the holograms / specklegram while the component is suitably stressed to give rise to differential displacement / strain around the defective region.In this paper, details of stressing methods, electronic speckle interferometry(ESI )applications and calibration studies for NDE of spacecraft structural components for NDE of different spacecraft components and the optical set up developed at ISRO Satellite Centre, are presented.
DEVELOPMENT OF STRESSING TECHNIQUESDevelopment of a suitable stressing technique for the NDE of spacecraft structural components is very important because of the special nature of the components. The holographic interferometry calibration studies [7,8] for NDE of honeycomb sandwich panels with thermal and vibration stressing have shown that the thermal stressing is suitable for panels made of aluminum alloy face sheet with only thick film adhesives (like 312) or panels made of carbon composite face sheets and not *rao@isac.gov.in and
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