Some wire insulation types have well-defined accelerated aging processes, whereas others are rather non-active in terms of standard aging (heat, strain, and humidity). This procedure provides a vetted process for assessing the age degradation process for polyalkene wire. For non-polyalkene insulated wire/cable types, see Thermal Index.
Life cycling of polyalkene wire is a three-step process that starts with placing the wire in a high-temperature air circulated oven for a defined period of time (according to MIL-W-81044 this is 200degC for a week). The temperature of the oven is monitored to ensure that there are no significant thermal variations during the course of the test. Once the high-temperature test has been performed, the length of wire is subjected to a bend test (described more fully under the bend test method). In this test, the wire is suspended from a mandrel with a weight attached to the free hanging end. At a defined pace, the mandrel is rotated with the wire progressively wrapped around the mandrel. The direction of the mandrel is then reversed and the process is repeated again.
The last part of the age degradation test for the polyalkene wire is for a wet dielectric test . In this, the wire is submerged within a salt water solution and a high voltage is placed on the conductor to identify cracks in the insulation. If current leakage is detected, then the wire has passed the age degradation testing. Progressive repetition of this process can be applied to determine the quality of existing wire on aircraft.
Test reports include pretest and post-test visual examination of the samples and the results of bend and dielectric testing.