Tremendous research and development effort was put forth in the past to find suitable structural materials for aircraft designs. Several stages of development were encountered. Different materials were tested and applied, at the various stages, to meet specific design requirements - wood, steel, aluminum, titanium etc. The latest development in aircraft and aerospace structures is composite materials, which provide high strength, high stiffness, corrosion resistance, ease of fabrication, lower weight and eventual fuel savings. The strength/stiffness-to-weight ratio of composite materials has been proved higher than metals.
Along with the development of materials, a very essential aspect is their maintenance and inspection. NASA, Boeing and other aircraft manufacturers have carried out a lot of research in the field. Only a few equipment are available at this time to enable effective inspection of composite material failures - delamination, disbonding, water ingestion, fiber fretting etc, which are quite different from metal failures.
Airline carriers face various problems caused by changes in concepts, material processes and systems in maintenance whenever new materials are introduced. The introduction of composite materials has brought with it new concepts of inspection and maintenance procedures unknown when metals were used. Many air carriers, in collaboration with aircraft manufacturers, were forced to upgrade their maintenance philosophies in order to cope with the latest developments.
Non-destructive-examination (NDE) is a major technique in composite aircraft structural materials inspection. Carefully evaluated and tested equipment for this purpose saves the airlines, especially small-to-medium sized, a lot of cost in terms of man-hours and acquisition and provides the best possible performance. Thermography is one of the best techniques developed. However, the cost of the equipment for this technique is high at this time.
Equipment selection for NDE of composite materials is the major theme of the presentation. It suggests that development in the field needs more effort to make further studies to arrive at appropriate equipment choices for airlines and aircraft maintenance facilities.
The main considerations in equipment selection are:
purpose of inspection
cost of acquisition of the equipment
Discussion proceeds from the above considerations. Data collection and equipment manufacturing firms as well as experience related issues are raised. The necessity for physical evaluation tests and financial constraints are emphasized for final recommendation and decision.