Signal-based bending stress monitoring using guided waves in hollow cylinders

This work provides a time domain approach to detect stress changes in hollow cylinders using low frequency ultrasound guided waves; the proposed scheme makes uses of the subtract method for stress level estimation. Residuals are generated by signal subtraction of the reference signal, at nominal condition, from the current signal. The stress condition is detected when the RMS of the residual goes above certain threshold. A simple supported hollow cylinder is utilized in this research and the different levels of stress, bending moment, are obtained using a vertical variable force applied in the middle of the specimen; the induced stresses are in the elastic region of the stress-strain diagram. The guided waves are generated via a couple of piezoelectric transducers operating in a pitch-catch configuration to excite and detect longitudinal and flexural waves. A Matlab® script is utilized to perform ultrasonic signal generation, signal acquisition and processing. Results of each stress scenario demonstrates the feasibility and potential of using this formulation in the evaluation of the bending stress in hollow cylinders. The studied monitoring scheme can be used on-line and it is a cost-effective approach