Diagnosing adhesive joints in laminar composites by ultrasonic flaw detection method

Abstract

In rocket and aviation technology, thin-walled elements shaped as casings, shields passages etc. which should be ready to operate under high mechanical loads are applied. In most cases, the operational and maintenance safety is strictly correlated with the expected reliability of these elements. These constructions often operate under additional exposure to heat, erosion and chemical influence of the flowing agent and their protection is therefore necessary. Any visual inspection of the glue joint quality is practically impossible. Up to now, the parts have been inspected manually by guiding the ultrasonic probe along the surface. Lack of special equipment caused difficulties connected with precision guidance of the ultrasonic probe along the examined surface. The article presents the arrangement and components of a computer measurement setup used to examine adhesive joints of thin-walled metal casings with laminar composites. The system makes it possible not only to measure, record and analyze the ultrasonic signal but also to present a graphical representation of the examination results. The use of special so-called broadband probes which generate very short (0.2 µs) pulses of longitudinal waves has made it possible to observe the influence which the quality of the bonding of the composite layer with the thin-walled steel casing has on the conditions of ultrasonic wave propagation inside the steel casing.