An investigation of stress determination for aircraft fatigue life estimation from in-flight strain data.

Abstract

A thorough knowledge of localized stresses due to geometric effects is necessary for accurate fatigue life estimation in aircraft structures. The Department of Aeronautics, Naval Postgraduate School, Monterey, California, has developed a strain monitoring system that provides data on nominal stresses experienced by aircraft structures, which can be applied to obtain local stresses at a stress concentration, provided a local stress vs. nominal strain relationship is available. A theory proposed by Neuber lends itself to development of a method by which local stress can be obtained with knowledge of nominal strain and material properties alone. Stress relaxation behavior was obtained for two cyclic loading histories of plate specimens in an effort to extend the monotonic local stress vs. nominal strain relationships into practical use for fatigue life estimation of aircraft structures.