Development of an ultrasonic dry-coupling inspection wheel for Online NDI composite application

Abstract

T he application of ultrasonic waves to the inspection of aeronautic compone nts is based on the use of couplants (water, gel, etc...) to facilitate the propagation of the sensi ng wave through the material. Although several solutions have been designed to integrate the use of these couplants and the NDT operations in different stages of component life (from production to in-service operation) its use incre ases the complexity of the process and the cost of the inspection because in some cases special infrastr uctures may become necessary. Some of the research effort developed in the last decades has been a ddressed to reduce the necessity of couplant gel or fluids. In this sense, the development of ultrasonic inspection w heels based on special rubbers with a high degree of humidity has been proposed and is being commercialized nowadays. How ever, its use is not allowed in applications where the condition of completely dry coupling is imperative. Other tools based on air-coupling have been also developed but they mainly operate in through transmission arrange ments and its use is limited to low frequencies. T his work examines a new wheel-based tool which can operate in dry condit ion . It has been developed in the context of the ICARO Project (Innovación en Composites Avanzados y Rear- End Optimizado) to provide a nondestructive inspection solution to be integrated into an Out of Autoclave ( OoA) composite manufacturing process based on electron beam curing technology layer by layer. T he solution requires be able to inspect very thin composite specimens (from 0.5mm) in clean and dry conditions compatibl e with the manufacturing process. T o overcome these conditions, a special inspection wheel prototype has bee n developed that integrates a 5MHz ultrasonic array transducer composed by 128 elements mounted in a particula r wedge. T his aperture operates in pulse-echo and generates an ultrasonic image based on linear scanning beam forming process and a synthetic aperture acquisition procedure known as 2R-SAFT . Inspection results obtained from reference standard of different thic kness are presented. T hese results are compared with conventional immersion UT inspections and show the high potentia l of this inspection wheel for this special applications.