Research On Damage Detection Of Sheet Using Lamb Wave Combined With Optical Sensing Technology

With the continuous progress and development of science and technology, more and more newthin plates are used in industrial manufacturing. These plates plays an significant role in vulnerablecomponents protecting, structure maintenance and load bearing due to its advantages, such as smallsize, light weight and excellent mechanical properties. Protection and support to the whole structurewould be reduced when thin plates get injured, even threaten the service life and safety of the entirestructure, therefore it is necessary to realize real-time online monitoring and active detection ofstructure health of thin plates.A fiber-optic Lamb wave detection system base on reflective intensity-modulation wasconstructed, according to the high sensitivity and fast measurement of Lamb wave combined with theadvantages of fiber-optic sensing, including immunity to electromagnetic interference, non-contactdetection. The optical online testing was realized and detection methods were improved.First of all, the principle, classification, characteristics and advantages of fiber-optic sensingwere introduced, especially the reflective intensity-modulation were elaborated. A fiber-optic Lambwave detection system base on reflective intensity-modulation was constructed. The system wascalibrated according to the use of figure hitting, pencil breaking and active Lamb wave testing.Results were compared with those measured by1045S broadband sound emission sensor, whichproved the actual detection capabilities. Signal denoising and peak extraction were also finished bythe use of wavelet because the low intensity and noise jamming of Lamb wave.Damage location and shape identification systems of LF21aluminum plate were constructed. Indamage location experiment, the damage coordinates calculated using triangulation algorithm andsensor array was11.5mm from the actual damage point. Making distance141.4mm from Sensor A asthe reference distance, the location error was8.1%, which had a high accuracy. In shape identificationexperiment, the hole of10mm diameter is tested by the use of stepping motor and scanning opticalfiber. Results showed that this method could realize a rough estimate of hole shape in thin plates.