NONDESTRUCTIVE EVALUATION OF METAL FATIGUE

Studies were conducted to improve and evaluate existing ultrasonic Rayleigh wave and magnetic perturbation equipment for the detection of fatigue damage in aluminum and steel stress cycled specimens. Ultrasonic results obtained from a 7075-T6 aluminum specimen stress cycled in direct uniaxial tension are presented; these include reproductions of Polaroid photographs of signal patterns and photomicrographs of the specimen surface showing the small fatigue crack detected. The recent results are compared with those of the previous program to indicate the improvement in resolution. On steel stress cycled specimens, both ultrasonic and magnetic technique results are presented including reproductions of typical data. These recent results are also compared with previous findings to establish the improvement in resolution. In addition, the fatigue detection results are compared with recent ones reported by other workers. Experimental investigations to determine the refraction properties of surface waves in laboratory size metallic specimens are described and the results discussed. These studies were conducted to obtain evidence that Rayleigh waves can be focused. (Author)