Reliable non-destructive inspection of composite materials in use in the aviation industry

Abstract

Fibre reinforced composite materials are increasingly being used in engineering applications in the aircraft industry as they display an excellent weight to strength ratio. The limitation on the use of these materials in load-bearing applications is largely brought about by the difficulties in inspecting these materials in a non-destructive manner. Also, the lack of mechanical behaviour data for these materials in general e.g. fractures toughness, which could provide information regarding the size of critical defects, contribute to the challenges in inspections. Various inspection technologies have been developed for the inspection of these materials. These include amongst others ultrasonic testing (UT), mechanical impedance or resonance testing, infrared thermography and laser shearography. The range of technologies and equipment are required to cope with the particular requirements of the varied composite materials and structures. No single inspection technology can cope with the variety of builds and style of construction. Although infrared thermographic testing (IRT) has been available for a number of years, the associated costs in applying his technology was generally too high to become a frontline inspection technology out in the field. The IR cameras available were bulky and also very costly. Of late the cost associated with the cameras has been reduced significantly through the use of bolometer technology, so that at present an IRT system can be purchased at more or less the same costs as a UT system which is designed to also inspect composite materials and structures. In order to investigate the possibilities in establishing an inspection capability for the composite manufacturing industry, funds were made available through the Advanced Manufacturing Technology Strategy (AMTS), to assess which technologies are available and to develop a capability in IRT for the country. This paper outlines the theoretical background on which the IRT is based and discusses a number of test scenarios where IRT was successfully applied in industry.