Assessment of incipient material damage and remaining life prediction with nonlinear acoustics

Abstract

Subjected to a wide spectrum of operational and environmental loads, engineering structures exhibit first signs of material deterioration at micro and meso scales. In contrast to nondestructive assessment of the macro-scale damage that resulted from material fracture, a limited number of technologies have tackled the complex task of detecting and monitoring the small-scale incipient damage. This paper discuses application of the nonlinear acoustic vibro-modulation technique for assessment of the micro/meso scale fatigue damage and remaining life prediction of metallic samples. A nonlinear acoustic damage index (DI), which indicates strength of the damage-induced nonlinear interaction of the high-frequency ultrasonic wave and the low-frequency structural vibration, was monitored during a set of strain-controlled fatigue tests. Stable growth of the damage index was observed at an increasing number of fatigue cycles showing correlation between DI and the micro/meso scale damage accumulation. This correlation allowed for introducing DI in the remaining life prediction methodology based on an entropy density criterion of local failure. Experimental testing confirmed the effectiveness of the proposed prediction approach. [Work supported by NAVAIR.]