NDTnet 1998 Aug, Vol.3 No.8

Full-Text - Abstract

High performance materials such as sandwich components are attractive materials for lightweight structures in aerospace, naval and automotive engineering. Their application to primary aircraft structures requires the knowledge of damage incurred after fabrication or in service. Honeycomb sandwich components are inhomogeneous and anisotropic materials with an extremely high sound damping. The ultrasonic imaging technique for these material must be capable of detecting all kinds of defects such as delaminations in the skin, debondings between skin and core and defects in the core (crushing). The inspections should beside to laboratory use be practicable for in-field inspections of 'real components. This requires the application of the echo technique because the components can only be handled from one side.

For this problem, optimizations of pulse parameters have been carried out. Only frequencies below 1.4 MHz can pass through the whole thickness. System components such as transducers, transmitter (pulser) and receiver had to be optimized. A water split coupling between transducer and component was used. Inspections of sandwich components with impacts (energies from 4 to 18 Joule)clearly displayed the defect areas in C- scans. B-scans delivered additional informations about the defect depths. Fig.1, a typical B-scan, shows echoes even in the core.

The experiences of the laboratory investigations were employed to in-field inspections of a ,,tail-unit" of the EH 101 helicopter. For the in-field recording of C- and B- scans a manual scanner was used. Defects such as impacts have been indicated with amplitude decreases of more than 15 dB. Due to time consuming for the manual scanning the MUSE-system (Mobile ultrasonic equipment) with a motor-driven manipulator and a special water circulation system for coupling has been developed. The MUSE provides ultrasonic imaging of components with optimized pulse parameters.

Fig. 1: B-scan of a sandwich specimen

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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