Aging wiring has become a critical issue to the aerospace and aircraft industries due to Shuttle and aircraft incidents. The problem is that over time the insulation on wire becomes brittle and cracks. This exposes the underlying conductive wire to the potential for short circuits and fire. The development of methods to quantify and monitor aging wire insulation is highly warranted. Popular methods of monitoring aging wire problems focuses on applying electrical sensing techniques that are

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... tive to the conductor's condition, but not very sensitive to the wire insulation's condition. Measurement of wire insulation stiffness and ultrasonic properties by ultrasonic guided waves is being examined. Initial laboratory tests were performed on a simple model consisting of a solid cylinder and then a solid cylinder with a polymer coating. Experimental measurements showed that the lowest order extensional mode could be sensitive to stiffness changes in the wire insulation. To test this theory conventional wire samples (typically found in aircraft) were heat-damaged in an oven, in a range of heating conditions. The samples were 12, 16, and 20 gauge and the heat damage introduced material changes in the wire insulation that made the originally flexible insulation brittle and darker in color. Extensional mode phase velocity increased for the samples that were exposed to heat for longer duration. The flexural mode was also examined as a means of measuring the insulation condition, but proved to be limited in application. Tensile tests were conducted on wire samples to measure stiffness changes. The trend of the tensile tests compared well to extensional mode measurements. Although the heat-damage conditions may be more extreme than environmental aging, indications are that this method has the potential to detect and quantify degradation in wire insulation.