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M. Vospernig, R. Heuer, M. Reiterer:
"Demonstration of Guided Wave Sensor Signals Effected by Cyclic Loads and Breathing Fatigue Cracks";
in: "Proceedings of the 6th European Workshop on Structural Health Monitoring 2012", C. Boller (ed.); issued by: German Society for Nondestructive Testing (DGZfP); European Workshop on Structural Health Monitoring - We.4.D.1, Dresden, 2012, ISBN: 978-3-940283-41-2, 643 - 650.

This paper presents an examination of ultrasonic guided waves (UGW) affected
by stress in the wave-guide. Detecting faults in structures with sparse sensor arrays
are widely established. The environmental influence of the sensor signals are
significant and have to be compensated when baseline concepts are used in the
sense of structural health monitoring. This investigation demonstrates, based on
experimental observations, deviations of sensor signals caused by a tensioned or
compressed wave-guide. To evaluate the behavior of the signal deviations a
numerical model is developed. Taking stress-stiffening into account, the change of
the sensor signals results from the deviation of the propagation characteristics.
Although the wave characteristics are multimodal, one mode, namely the flexural
A0 mode, is extracted and the signal deviations are reduced in the space domain.
This is performed by a dispersion compensation process and the adaption of the
dispersion curves to the stiffness of the wave guide. The procedure is applied to the
numerical and the experimental signals and the improvement in the accuracy of the
residual signals is presented.
INTRODUCTION