Insulation aging from simultaneous mechanical strain, polymer-chemical, and temperature interactions

A theoretically based multistress life relation is developed for aromatic polyimide insulated wire, military specification type MIL-W-81381. The stresses are water, temperature, and mechanical strain. The energy states, chemical mechanisms, diffusion constants, and molecular energy versus strain relationships are so complex that the authors are not capable of ab initio derivation of constants. As an alternative, over 1300 specimens have been tested from 1981 to 1991. The results fit the theoretical trends and reduce to the classical Arrhenius curve for a two-parameter function. The three-parameter effect is being applied to data from laboratory aging experiments that are simulating the deterioration that is occurring in actual aircraft service experience