Transducer Arrangement for Baseline-Free Damage Detection Methods With Guided Waves

Structural Health Monitoring (SHM) refers to methods for the early detection of damage in components in order to initiate planned repair. Acoustic methods using guided waves are widely established for the monitoring of large-area, thin-walled structures. Current SHM approaches based on active ultrasonic techniques use the knowledge of a known reference condition of a considered transmit–receive path, with which all subsequent conditions are compared, in order to obtain a statement about the local component condition. In most cases, these methods evaluate amplitude or phase changes with respect to the reference signal. The dependency of the signal evaluations on environmental influences such as temperature or humidity changes makes it necessary to explicitly consider these influences through statistical analyses and background knowledge on the material side or to provide different reference states known as baselines for different environmental conditions. The subject of this study is the development of baseline-free methods. The focus is on the identification of the damage interaction of the guided waves and the mode identification by suitable transducer arrangements for the determination of structural damage on reciprocal sensor transmission paths. For this purpose, parameterized simulation experiments were performed to investigate different arrangements of piezoelectric transducers for wave mode identification and to validate their results in laboratory measurements. It could be shown that stacked transducers can be used for wavemode identification. Further more an additional effect of phase shifts in between two wavemodes was observed using a piezoelectric ring transducer with two electrode pairs.