Service Life Prediction of Composite Structures Through Fiber Testing.

Increasing the severity of the stress history of a structure reduces it's service life. Feasibility studies to increase the zero fuel weight of the P-3 Orion depend heavily on the resulting decrease in service life of the wing box and airframe. One option of extending the service life of existing aircraft is through the replacement or augmentation of critical structural members with composite materials. Since structural composites do not yet have adequate service life statistics, life predication must be through probability modeling. Such modeling can begin with experimental data on accelerated testing of fiber life under several sustained load levels. This data can be the basis for an appropriate strength-life model of the fiber which can in term be related to the strength-life model of the composite by the local-load sharing model. The local load sharing model captures the physical failure sequence of fiber failure within a composite. Such a strength-life model, when combined with structural analysis, can be used to predict an airframe's service life under the changed conditions associated with the zero fuel weight increase. Service Life, S-N Curve, Weibull, Maximum likelihood estimators break down rule.