As part of the development of a Structural Integrity Prognosis System (SIPS), two outer wing panels from a retired aircraft have been destructively examined.  The results of this examination will be used to compare the actual damage observed with that predicted by the various models being employed in the program.

Two outer wing panels that were recently retired from service were investigated.  They had been fabricated in the late 1970’s and were flown until their fatigue life was judged to be expended.  The critical area of the panel was the row of fastener holes in the lower wing cover where it was attached to rib 1.  This area of the wing cover was cut out, and the fasteners carefully removed.  The condition of each hole was documented, and the corrosion protection coatings were characterized and removed using a two-step procedure.  The condition of the holes was documented at each phase of the coating removal process.  Eventually, all of the fatigue cracks and manufacturing defects were photographed and their sizes and locations documented.  Approximately thirty holes in each panel were analyzed.  Crack initiation was found to be primarily associated with constituent particles and/or cracks in the anodized coating.  Manufacturing defects (e.g. scratches, gouges, grooves, etc.) accounted for only a small fraction of the cracking.

*This work is partially sponsored by the Defense Advanced Research Projects Agency under contract HR0011-04-C-0003.  Dr. Leo Christodoulou is the DARPA Program Manger