Non-destructive testing of future rocket boosters using air-coupled ultrasound

Abstract

Air- and space craft vehicles are constructed from an increasing amount of carbon fibre reinforced plastics (CFRP). In particular, the European Space Agency’s (ESA) future launch vehicle Ariane 6 is intended to have a solid rocket motorcase (booster) fabricated from CFRP for the first time in order to save weight and therefore enable Ariane 6 to work more efficient. In the frame of the joint research project ComBo (Effiziente Fertigungstechnologie für Composite Boostersegmente - efficient fabrication technology for composite booster segments) a pressure vessel had been designed and manufactured by MT-Aerospace to prove production technology for the final rocket booster. In ComBo, the Center for Lightweight Production Technology (ZLP) of the German Aerospace Center (DLR) covered the non-destructive inspection (NDI) of the pressure vessel by using air-coupled ultrasonic testing (ACUT) in reflection mode. In this paper we show the pressure vessel with its high demands regarding testability and outline the physics of lamb waves and working principles of ACUT as well as its advantages over water-coupled ultrasound. The high-end capabilities of the ACUT device and -procedure applied at DLR/ZLP as well as measured C-scans and the automated detection of flaws on it are presented.