In ultrasonic structural health monitoring (SHM), environmental and operational conditions, especially temperature, can
significantly affect the propagation of ultrasonic waves and thus degrade damage detection. Typically, temperature
effects are compensated using optimal baseline selection (OBS) or optimal signal stretch (OSS). The OSS method
achieves compensation by adjusting phase shifts caused by temperature, but it does not fully compensate phase shifts
and it does not compensate for accompanying signal amplitude changes. In this paper, we develop a new temperature
compensation strategy to address both phase shifts and amplitude changes. In this strategy, OSS is first used to
compensate some of the phase shifts and to quantify the temperature effects by stretching factors. Based on stretching
factors, empirical adjusting factors for a damage indicator are then applied to compensate for the temperature induced
remaining phase shifts and amplitude changes. The empirical adjusting factors can be trained from baseline data with
temperature variations in the absence of incremental damage. We applied this temperature compensation approach to
detect volume loss in a thick wall aluminum tube with multiple damage levels and temperature variations. Our specimen
is a thick-walled short tube, with dimensions closely comparable to the outlet region of a frac iron elbow where flow-induced
erosion produces the volume loss that governs the service life of that component, and our experimental sequence
simulates the erosion process by removing material in small damage steps. Our results show that damage detection is
greatly improved when this new temperature compensation strategy, termed modified-OSS, is implemented.
Peng Gong, Thomas R. Hay, David W. Greve, Warren R. Junker, and Irving J. Oppenheim, "Compensating temperature-induced ultrasonic phase and amplitude changes," Proc. SPIE 9803, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2016, 98033K (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 24, 2016; Published: 20 April 2016); https://doi.org/10.1117/12.2218899.
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