Residual lifetime prediction in aerospace structures using wholefield laser strain techniques

Abstract

The manufacture of aircraft components requires quality control procedures and mechanisms to identify potentially defective units during manufacture, testing stages as well as during service life. Defects can be formed due to random or systematic errors within the manufacturing process and comprise of tiny fatigue fractures within the wheel structure. Use of such defective wheel and tyre units by an aircraft operator could for example least to growth of these fractures, which in turn can generate sudden unexpected catastrophic failure on landing. Qualification and approval of all wheel units is mandatory under UK Civil Aviation Authority (CAA) and US Federal Aviation Authority America (FAA) regulations as well in the aircraft manufacturer standards. The regulatory authorities and manufacturers were requesting improvement in testing and traceability of, analysis methods during manufacture and during routine in service maintenance checks. They were thus considering alternative technologies. Speckle shearing interferometry is a non-contact wholefield sensor system used primarily within the aerospace industry, for analysis of defects in composite materials, including the analysis of manufacturing defects in aircraft tyres. This methodology has traditionally been used qualitatively to identify the location of faults such as disbands. Through laser technology and image processing technology advances, it has become more common for this type of instrumentation to deliver quantitative data. However there has been concern about data integrity, data quality and issues of defects being missed due to instrument sensitivity.