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Degradation Kinetics of Aerospace Wire Insulation Material
Peter R. Hondred 1 , Sungho Yoon 1, 2 , Nicola Bowler 1 , and Michael R. Kessler 1 *
1 Department of Materials Science and Engineering, Iowa State University
2220 Hoover Hall, Ames, IA, 50011, USA
E-mail address: mkessler@iastate.edu
2 School of Mechanical Engineering, Kumoh National Institute of Technology
Yangho-Dong, Gumi, Gyeongbuk, 730-701, KOREA
ABSTRACT
The past conventional wisdom that aerospace wire insulation failures such as cracks, fraying,
and degradation are atypical and harmless has proven to be a costly liability exhibited in the tragic
accidents of Swissair 111 (Nova Scotia, 1998) and TWA 800 (Long Island, NY 1996). These accidents
have been attributed to damaged wiring insulation caused by degradation, cracking, and fraying; a
problem for many miles of wire buried deep within their structures. As the aerospace industry matures,
hundreds of failures are being discovered in typical aircrafts. Consequently, it is imperative to
understand the cause of the failures. However, despite the importance of understanding the
mechanisms and kinetics of wire degradation under various thermal, environmental, and mechanical
loadings, no systematic studies has been reported on the thermal degradation kinetics of typical wire
insulation materials.
This work investigates the thermal degradation kinetics of three commonly used wire insulation
materials, poly(ethylene-alt-tetrafluoroethylene) (ETFE), poly(tetrafluoroethylene) (PTFE), and
poly[(5,7-dihydro-1,3,5,7-tetraoxobenzo[1,2-c:4,5-c']dipyrrole-2,6(1H,3H)-diyl)-1,4-phenyleneoxy-
1,4-phenylene] (Kapton) through the use of thermogravimetric analysis (TG).
TG measures the degree of degradation (as measured by mass loss) with respect to time (t) and
temperature (T). The degree of degradation (α) can be defined as:
where wt% is the relative mass obtained directly from the TG experiment.
When modeling, two separate functions are assumed, K(T) and f(α), such that the governing
differential equation has the following form:
where is the rate of degradation, K(T) is the temperature-dependent rate constant, and f(α)
corresponds to the reaction model. The temperature-dependent rate constant is commonly described by
the Arrhenius equation:
(3)
where R is the universal gas constant, E is the activation energy, and A is a pre-exponential factor. The
reaction model is chosen based on isoconversional analysis techniques.
When heating at a constant rate, the equation can be redefined to eliminate the time-dependence
by dividing through the differential equation by the heating rate:
(1)
(2)
Society of Engineering Science ▪ 47 th Annual Technical Meeting 36