Abstract Summary
3D printing (additive manufacturing, AM) is a promising approach for the production of light and strong structures with many successful applications, e.g., in dentistry and orthopaedics. Numerous types of filaments differing in mechanical properties can be used to produce 3D printed structures, among others, polymers, metals or ceramics. Thanks to the ease of the manufacturing process, the wide use of biodegradable polymers is observed, e.g., polylactide (polylactic acid – PLA) and polyvinyl alcohol (PVA) with a practical application as soluble support for manufacturing complex-shaped elements. The current work dealt with the application of ultrasonic guided waves for non-destructive damage detection and imaging in AM plate elements. Different specimens were considered. The first one had an area of 100 x 180 mm2 and a thickness of 2 mm and was only made of PLA filament. It had structural defects in the form of voids, one being a total lack of material and three with different meshed fillings. The second one had the same surface area but its thickness was equal to 3 mm. The specimen was also made of PLA, however, some PVA inserts were introduced, thus it could be considered a composite structure. Each specimen was tested using the same algorithm. Guided waves were excited using a single PZT actuator and recorded contactless with the use of scanning laser Doppler vibrometry (SLDV) at a set of points spread in a regular grid located on one surface of the sample. Additionally, numerical finite element models of analysed samples were prepared using Abaqus/Explicit software. The real structure of the prepared plates was reflected using volume finite elements with a grid size of 1 mm. The wave excitation was simulated as a concentrated force with varying amplitude. The signals of propagating waves were registered in the same area as in the experiment. The collected signals were processed using the weighted root mean square (WRMS) algorithm. The processing was performed with different values of calculation parameters, namely, time of averaging (time window), determining the part of the signal taken into calculation, and the weighting factor, differentiating the influence of specific parts of the signal due to the time of propagation. The WRMS damage maps for both samples were prepared to differentiate intact and damaged areas. It was observed that the type of defect strongly influenced the efficiency of imaging. The limitations of the proposed approach were characterized. The presented results confirmed that guided waves are promising for non-destructive damage imaging in AM elements.
