Quantitative Assessment of Thermal Liner Delaminations in Large Size Composite Rocket Boosters for its Repair using X-Ray Radiography

Advent of long range rocket motor has inevitably forced the designers to accord prime importance to the low weight and high strength materials and thus composites are preferred. Technological challenges in manufacturing a composite material large size rocket booster are enormous and therefore production of a defect free motor is a formidable challenge. The metal shell and composite shell both of them have thermal liner, but unlike metal shell, composite shell does not support Ultrasonic Echo Technique for bond evaluation prior to propellant filling. Ultrasonic Transmission Technique has its own limitation for the quantitative assessment of gaps. With the current processing methods, unlike metal shells, delamination occurrence between composite shell and thermal liner are more frequent and critical in nature. Tap Test give quick view of the bond integrity of thermal liner, but in few cases, delaminations are evident by naked eyes and it looks like a hump. Here lies a scope for the rectification of hump. This paper presents the adopted technique for providing insight into hump and quantitative assessment of the de-lamination by evaluating angular & radial extension, gap, surface area and volume using RT (Radiographic Testing). Apart from tap test, RT revealed additional delamination areas. The mapped details helped the engineers in visualizing the internals of hump and designing a suitable repair scheme. Then after, the soundness of repair process was confirmed by RT and cleared for further processing. The entire exercise was validated by a successful static test. The post test evaluation of the repaired zone was performed using RT. Here, RT played a vital role and the efforts put from investigation to rectification of the problem generated good data & gives enough confidence to tackle problems of similar nature in future.