ACOUSTIC EMISSION TECHNIQUE - AN EFFECTIVE TOOL FOR THE INTEGRITY EVALUATION OF M250 MARAGING STEEL AEROSPACE PRESSURE CHAMBERS
T. Chelladurai*, A. S. Sankaranarayanan*, S. V. Subba Rao$, AVSSSR. Sarma*, A. R. Acharya*, R. Krishnamurthy** *Vikram Sarabhai Space Centre, Trivandrum 695022, India $Sriharikota Range Centre, Sriharikota 524124, India **Indian Institute of Technology, Madras 600 036, India
Acoustic Emission (AE) technique has demonstrated capability for the structural integrity evaluation of pressurised systems. The technique has been employed where real time evaluation of the hardware is warranted particularly the ones which are fracture prone. In the aerospace industry application of low alloy high strength materials such as M250 maraging steel forpressurised systems forming the lower stages of launch vehicles is common place. The hardware bear a low margin of safety. As such there is an undesirable possibility of any of the active defects or discontinuities located on the highly stressed regions of the hardware leading to catastrophic failure during proof pressure or acceptance testing. Such costly failures can be effectively averted in real time by making judicious use of AE technique followed with appropriate remedial measures by way of repairs etc. Acoustic Emission technique identifies active discontinuities in terms of AE parameters, the severity can be assessed quantitatively based on high energy AE emissions which are characterised by high amplitude long duration events. Any quantitative evaluation requires certain guidelines or criteria evolved based on comprehensive studies done at specimen as well as sub scale chamber level. The paper describes the lab. scale studies carried out as above on M250 maraging steel [1] and the criteria - both acceptance and abort - evolved there from particularly to suit large pressure chambers. The criteria is based on governing AE parameters like event rate, high amplitude emissions, long duration events and roll over of emissions during pressure hold etc. [2]. An empirical formula deduced from the governing AE parameters to estimate the margins on the pressure chamber is also covered in the paper. The AE monitoring and evaluation carried out on a large number of large size pressure chambers bearing known and unknown cracks and other defects are summarised. The refinements being contemplated to enhance the margin of prediction is also discussed in the paper. REFERENCES
T. Chelladurai et al, "Acoustic Emission Response of 18% Ni Maraging Weldment with Inserted Cracks of Varying Depth to Thickness Ratio", Materials Evaluation, Vpl. 53, No. 6, pp. 111-115, 1995.
T. Chelladurai et al, "An Approach for the Integrity Assessment of M250 Maraging Steel Pressurised Systems", Journal of Acoustic Emission, Vol. 8, No. 1-2, pp. S88-S92, 1989.
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 2409 - 2412 Publisher:Ashgate Publishing Company
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