The Problem
The use of Non-Destructive Testing (NDT) for defect detection is of primary concern to material producers and
aircraft manufacturers. The risk of failure with its associated potentially catastrophic consequences could
lead to a lack of consumer confidence that can signal the ruin of a particular design and on occasion the
responsible organisation. Defects in titanium alloys are considerably different from those encountered in
traditional aerospace materials. This means that the proven NDT techniques that exist for inspection of
defects in more traditional aircraft structures are not applicable for use in this advanced multi-functional
material. Furthermore, existing NDT techniques currently applied have diminishing usefulness as increased
production rates, operator subjectivity and fatigue drastically decreases the probability of defect
detection (POD). The crash of flight UA 232 at Sioux City, Iowa, USA in July 1989, with 111 fatalities, was
directly attributable to a fatigue crack initiating from a hard alpha inclusion on the surface of a turbine
disc that was not detected during billet manufacture. Other reports, of similar aircraft incidents involving
fatalities have concluded that the current in service NDT inspections had failed to detect defects created
during the manufacturing process that subsequently became responsible for the loss of life. In order to
combat the current failings in material inspections and ensure such catastrophes are kept to an absolute
minimum, extremely conservative component lifing policies are operated by the airline industries. These
lifing polices have crippling effects on airline costs which in turn hinders the potential for expansion of
titanium utilisation and the previously mentioned benefits which could be realised. This illustrates the
urgent need to develop new advanced NDT technologies for application during the manufacture of titanium
destined for aircraft components. Figure 2 shows the catastrophic effects of such failures.
Figure 2. Engine failure following the lack of detection of a Hard Alpha inclusion and the impact of failures.
