Residual Life Predictions of Composite Aircraft Structures Via Nondestructive Testing, Part 2: Degradation Modeling and Residual Life Prediction

In the second part of this two part paper, we present a residual life prediction model for the Harrier AV-8B horizontal stabilizer (see part 1 in the September 2000 Materials Evaluation, Vol. 58, No. 9, p 1065). The margins of safety of composite structural components throughout the horizontal stabilizer are used to define its structural integrity state. Specifically, we conclude that when any of the strength, stiffness, or stability margins of safety has been sufficiently reduced via any combination of damage mechanisms, the horizontal stabilizer may be said to have operationally failed and thus must be replaced or repaired. Via the horizontal stabilizer's design margins of safety and empirical models for the degradation of composite laminates, we devise margin of safety deterioration surfaces and operational failure criteria that depict the functional dependence of residual life on the local losses of strength and stiffness throughout the structure. Our results establish an analytic framework that can be applied not only to the Harrier AV-8B horizontal stabilizer, but also to a broad class of composite aircraft structures.