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Internal Defect Detection in Composite Plates on Demand



The motivation for this research is a lack of accurate, efficient and costeffective methodology to detect internal defects in composite plates. A micro-size network of strings is interwoven into the composites. Each string consists of a pair of tubes, containing one of two different non-polar reactants. A local defect within the composites causes straining and cracking of the tube shell, resulting in the direct contact of the two non-polar reactants. The latter undergo a chemical reaction resulting in a polar product. Our preliminary investigation shows that a polar product, when exposed to a microwave energy source, heats up dramatically in comparison to the ambient composite material or the non-polar reactants. Our proposed structure-health monitoring approach builds upon this finding by using a short term low-power microwave exposure, causing a local high-thermal signature along potential internal defects. The elevated temperature regions are visualized with an infrared camera. The research presented in this paper has the following objectives: (a) We introduce adequate non-polar reactants and quantify the temperature sensitivity of the polar product. (b) We investigate the optimized microstructure and material of the double-cell tube and fine-tune the design to enable fracturing of the cell walls under certain strain and ease embedment into the composites. (c) The paper sheds light on potential manufacturing processes of the micro-size sensing network per se as well as the embedment into the composites. The clear advantages of this methodology over others are that it provides large area coverage, has no requirement for an internal power source and wiring and hence does not compromise the structural integrity of the composites.

doi: 10.12783/SHM2015/214

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