Composite materials have gained importance in various fields because of their properties like higher specific strength, higher specific stiffness, corrosion resistance etc. They are used as ablative nozzle liners in aerospace sector for functioning under high thermal and erosive environments. Quality assurance is very important for these composite liners, being critical components of launch vehicles and rockets. Defects like delaminations, low density regions can significantly change the erosion rate of these liners thereby leading to mission failure. Till now, radiography testing (RT) has been the primary NDT technique for composite liners. Thicker and larger diameter nozzle liners need very high energy for taking tangential radiography thereby necessitating linear accelerators. Ultrasonic testing (UT) is introduced with the aim of reducing/replacing radiographic testing. UT using liquid couplant is to be avoided while testing because of the porous nature of these composite liners, as the liquid couplant may ingress inside the liner thereby affecting performance and further processing. In this paper, the application of air-coupled ultrasonic system for the NDT of nozzle liners using through transmission mode is discussed. Air-coupled Ultrasonics is an emerging non-contact ultrasonic technique which avoids the physical contact between the transducer and material being tested. The transducers and equipment are designed to reduce the energy losses occurring due to acoustic impedance mismatches. Finite element analysis is performed using the general-purpose finite element package-ABAQUS to simulate the wave propagation in composites with air-coupling and to study the interaction of wave with defects in composites. Experimental studies are carried out on composite specimens. A specially designed seven axis manipulator system is used for the quick scanning of the nozzle liners with air-coupled transducers.
Air-coupled ultrasonics. Modelling and experimental studies for thick composite liners
Luftgekoppelter Ultraschall. Modellierung und experimentelle Untersuchung von dickwandigen Komponenten aus Verbundwerkstoff
2009
5 Seiten, 5 Bilder, 1 Tabelle, 5 Quellen
Conference paper
English
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