Implementation of Signal Processing Methods in a Structural Health Monitoring (SHM) System based on Ultrasonic Guided Waves for Defect Detection in Different Materials and Structures

摘要

The local defect inspection in longitudinal structures such as plates or pipelines implies highudeconomical costs and it is time consuming mainly in underground infrastructures, energy orudwater, and aerospace sectors. Moreover, if these structures are non-accessible, their localudinspection is not possible. Ultrasonic (US) inspection technique based on guided waves isudone of the potential alternatives to address this issue. The US inspection based on these typeudof waves could be applied in many scenarios to monitor the damage state of structures; i.e.,udin water underground pipelines to identify the wall thickness losses or impact damageuddetection on Carbon Fiber Reinforced Composites (CFRC).udA SHM system based on guided waves requires a special signal processing in order toudidentify possible damage in the structure. The signal emitted and received is a combination ofuddifferent propagation modes which are difficult to identify and analyse. However, if theudsignals are compared to each other (signal related to non-damaged components compared touddamaged signal) it is possible to measure their difference as a distance that can be used toudestimate the damage level.udIn this work, signals corresponding to non-damaged samples have been captured and thenuddifferent types of damage have been applied for different cases. After the data acquisitionudphase, the comparison between signals has been carried out by applying differentudmathematical methods and distance metrics (SDC, DTW, Euclidean, Manhattan andudChebyshev), with the aim of detecting defects in different structures and materials. For thisudpurpose, two cases have been analysed: 1) In CFRC plates subjected to impact damage anduddeformations and 2) In a pipe coated by cement-mortar in order to quantify the walludthickness losses.udIn both cases ultrasonic PZT sensors, an ultrasonic multichannel pulser/receiver and audsoftware developed ad-hoc have been used. Although the SHM system components wereudsimilar, it must be noted that the type of ultrasonic guided waves used were different; in theudcase of CFRC plates, Lamb waves were excited whereas in the case of the pipeline, Loveudwaves have been used. A comparison between the above mentioned methods is provided. Theudresults show the validity of the approach for damage characterization.