| Based on a survey of aging aircrafts, critical elements in skin structures and their failure mechanisms were identified A global guided wave approach we proposed as a reliable and economically efficient NDI technique. Resonance matching and mode selection tools were developed following solutions to boundary value problems of an infinite plane wave incidence in single and multi-layered media, treated with a physical insight provided from a partial wave technique. Dispersion curves for a three layer media were analyzed to seek sensitive modes for cohesive and adhesive weakness detection. Influence of finite size transducers on guided wave excitation and subsequent implementation in probe design was addressed. The utility of the developed tools to solve practical problems in aging aircrafts was demonstrated both on laboratory fabricated specimens and on the Boeing 737 test bed at the AANC facility of the Sandia National Laboratories, Albuquerque. Protocols and procedures were laid out to handle inspection of unknown structural geometries. A Double Spring Hopping Probe (DSHP) was developed to handle curved surfaces and was also tested on a Boeing test bed. |
