Low-frequency acoustoelastic-based stress state characterization: Theory and experimental validation

In this work, a new model-based stress measurement technique is developed. The technique integrates the acoustoelastic theory with numerical optimization and allows the utilization of the highly-stress-sensitive, strongly-dispersive, low-frequency flexural waves for reference-free stress measurements. The technique is experimentally validated on a long, rectangular aluminum beam, where accurate stress measurements have been achieved at low excitation frequencies. For instance, with a 500 Hz excitation signal, the error in the measured state-of-stress is found to be in the order of 1 MPa for the different loading scenarios considered in this study. Experimental results show that the developed technique is capable of measuring the state-of-stress without the need for calibration at a known stress state, which makes it ideal for in-service structures.