Aging in wire insulation under multifactor stress

Abstract

A fundamentally based chemical-thermodynamic multifactor stress aging functional relation requiring experimentally based constants is developed. The specific example presented is that of 120-V aromatic-polyimide-insulated wire. The stresses of water, temperature, and mechanical strain are included and electrical stress is considered. The results for over 2000 specimens are fitted to the theoretical trends. For a single independent variable function, the resulting relation reduces to the classical Arrhenius curve. The three independent variable relations presented here are applied to data from laboratory aging experiments that simulate insulation deterioration occurring in actual aircraft service. The results used in age categorization of US Navy aircraft are taken from wire specimens taken from active aircraft. The paradigm does not use ab initio based constants because of uncertainties in the theoretical development, two forms of which are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>