Analysis of digitized on-site ultrasonic state measurements

Abstract

Of concern is noninvasive gage-less monitoring fatigue experiments as well as detection and tracking of cracks, surface, and bulk. Accordingly, a digital signal decomposition method is developed for the analysis of sharp, time-limited ultrasonic pulses traveling through a tensile specimen on-site. The method extracts from the propagating pulses, respective elongation, and diameter reduction due to stress, associated with signal delays and changes in amplitude and shape. The analytical process is based on a nonlinear multivariate regression analysis. When applied to the current experiments, the method extracts delay variations accurate to the order of ±1 ps and quantified signal-deformation data. These results relate to a tensile-stress experiment under a five-cycle strain-cycle experiment, extending some of the cycles well into the plastic regime of a stainless steel specimen. The three-section cylindrical specimen consists of two gripper heads and a slender cylindrical section 6 mm in diameter and 20 mm long. Transducers are implanted on both specimen faces along the main axis [Mostafa et al., Int. J. Fract. 85, 99–109 (1997)]. [Work supported by NASA.]