PSI - Issue 14

V. Viswanath et al. / Procedia Structural Integrity 14 (2019) 442–448 V Viswanath/ Structural Integrity Procedia 00 (2018) 000 – 000

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5. Results and Discussion

The propellant tank had withstood the room temperature proof test at pressure of 0.46MPa (absolute). Positive margin of safety, against failure by fracture, is observed for the welds in presence of the three minimum detectable crack sizes. At cryogenic temperature, there is an increase in strength and plane strain fracture toughness of the welds by 30% and 10% respectively compared to room temperature (proof test is carried out at RT). Moreover, with the operating pressure being 0.43MPa (absolute), the reference stress is also lower. These factors together contribute to increasing the margin of safety against failure from fracture mechanics point of view. 6. Conclusion The structural integrity of the weld region of a propellant tank used in a new generation launch vehicle, in presence of high welding residual stress, has been evaluated from fracture mechanics point of view. Positive margins against failure by fracture are observed for RT proof test. With the weld having higher toughness at cryogenic temperature and with lower reference stress, higher margin of safety against fracture would be available while in operation. References Koichi Masubuchi , 1980, ‘Analysis of welded structures, residual stresses, Distortion and their consequences’, 1 st Edition, Pergamon Press. J.C Newman, Jr& I. S. Raju, 1984, ‘Stress Intensity Factor Equations for Cracks in Three -Dimensional Bodies Subjected to Tension and Bending Loads’, NASA TM 85793, NASA, Hampton, Virginia, USA Anonymous, 1996, ‘fracture Control Requirements for Payloads Using the Space Shuttle’, NASA STD 5003, Anonymous, 2005 ‘Guide to Methods for assessing the acceptability of flaws in Metallic Structures’, BS7910: 2005, British Standards Institute. T. L. Anderson, 2005, ‘Fracture mechanics - Fundamentals and Applications’, 3 rd Edition, CRC press, Taylor & Francis group UweZerbst, Manfred Schödel, Stephen Webster, Robert A. Ainsworth, 2007, ‘Fitness -for-Service Fracture Assessment of Structures Containing Cracks’, Academic Press. Anonymous, 2005, ‘NASA FLAGRO material database’,