NONDESTRUCTIVE DETECTION OF STRUCTURAL DAMAGE UNIQUELY ASSOCIATED WITH FATIGUE

摘要

The program was directed at the development of reliable nondestructive testing and inspection methods to locate and assess fatigue damage in Air Force aircraft structures. The primary nondestructive test approach is the application of exoelectron emission to the detection of fatigue damage. Initially, a series of controlled fatigue tests were conducted in an ultrahigh vacuum chamber to fully characterize the surface state of the specimen prior to, during, and after fatigue measurement. Next, a series of fatigue tests were conducted in air on specimens of different shapes with and without discontinuities under various loading and environmental conditions, in order to develop a practical technique for applying exoelectron emission and surface potential difference measurements to assess fatigue damage as well as to predict final failure sites. A porototype system design for the automatic scanning and exoelectron emission testing of aircraft-type structures was developed.