Ultrasonic guided wave inspection of a 747 tear strap structure

An efficient guided wave inspection technique for a 747 tear strap inspection problem in the flight deck region is presented in this paper. The approach represents an alternative to normal beam pulse echo or resonance inspection. Many researchers have examined the possibility of inspecting aging aircraft skin structures using guided waves. Benefits over traditional point by point, normal beam ultrasonic or resonance include simplicity of data analysis, sensitivity due to longitudinal and shear type particle motion, and inspection in a line by line fashion vs. point by point. Previous feasibility studies have been carried out on adhesively bonded, Boeing 747 and 737 tear strap and lap splice samples using through transmission and pulse echo techniques. Two of the drawbacks of these studies were the necessity of using liquid couplants to introduce the ultrasound to the structure and the expense of the equipment. To solve these problems, dry contact couplants along with inexpensive, standard flaw detectors and narrow band probes were used to carry out the inspection.