Advanced Ultrasonic NDT of Aero Engine Components Using Standard Transducers and Optimized Mirrors

The inspection of complex-shaped components can suffer from the fact that the area of interest can not be properly insonified due to restricted access. In such cases, mirrors can be applied to turn the ultrasonic beam onto the component’s surface. In this paper, the optimization of such a mirror is illustrated for a specific application in aero engine inspection. Its shape has been designed to compensate the influence of the curved component surface on the ultrasonic beam field and to additionally achieve a focusing of the beam. Introduction The application of new manufacturing processes increases the need for advanced inspection techniques. This especially holds for ultrasonic NDT of complex components which generally suffers from loss of sensitivity, beam distortions and beam misorientations if the transducer is not perfectly matched to the specimen. A procedure which allows to optimize single and multiple element transducers to ensure a proper focusing of the beam field in the range of interest has been presented recently, accounting for the specific inspection configuration under concern [1]. The simulation method is based on delay time calculation for multiple element transducers and employs a superposition technique for beam field calculation. In inspecting aero engine components where the area of interest can not be properly insonified due to restricted access, the use of mirrors to turn the ultrasonic beam onto the components surface has proven to be efficient. Modifying the above mentioned simulation approach we have performed an optimization of such a mirror, where its shape has been designed to compensate the influence of the curved component surface on the ultrasonic beam field and to additionally achieve a focusing of the beam in the area of interest. Simulation as well as experimental results are shown for an engine component, where inspection has been performed applying an unfocused, circular transducer at 25 MHz frequency. Specifically obtained results on eroded notches in a blisk dummy demonstrate the efficiency of the new approach. The aero engine component to be inspected, a bladed disk, is shown in Fig. 1. Here the blades are welded onto the disk through a linear friction welding process (bladed disk = blisk). The inspection of such components, where a new welding process is ECNDT 2006 We.2.1.4