Aircraft wire degradation often means a reduction in a wire insulation’s ability to withstand physical, electrical, or chemical strain. Such reductions can lead to insulation breaches, which can result in system interruption.
All modern wire insulations are long chains of molecules called polymers. Over time, due to various types of stress, there is wire degradation. One mechanism for wire degradation is exposure to elevated temperatures or mechanical stress that cause the bonds between polymer chains to brake and shorten (this can sometimes be identified by measuring the molecular weight of the insulation). These shorter chains typically will present as a weaker insulation that is more likely to break during mechanical movement (bending, stretching, etc.).
Another mechanism for wire degradation is exposure to intense light or high-energy radiation (UV, x-ray, etc.). Called ‘photolysis’, this is the process in which light causes a chemical reaction within the polymer. Sections of the polymer break down and, in some insulating materials, cause the release of hazardous gases.
Wire degradation may also be caused by oxidation, particularly at elevated temperatures. Oxygen in the atmosphere can attack the surface of the material, resulting in a weakening at locations along the polymer chain.
How a particular wire degrades is as much about the environment in which it operates as it is about the manufacturing process that created the wire. Variability in the base materials, additives, and fabrication process can result in premature wire degradation.
In some cases, if wire degradation is suspected, the easiest course of action is to replace the wiring. However, when this becomes cost prohibitive, technologies can be employed to determine the level and scope of the wire degradation. These technologies can assess if there is a wire degradation issue, and determine if immediate action is necessary.
There are a number of techniques that can determine the state of wire degradation. Technologies as WIDAS, Inherent Viscosity, DelTest, and Wirelytics (all offered by Lectromec) provide a scientific basis for determining wiring system conditions. Each technology is based on extensive lab research and field tests evaluating the different degradation paths for a variety of wire insulations. The application of each is dependent upon the system being investigated.