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Precise Monitoring of Damage Evolution in Laminated Composite Materials Using Integrated Carbon Nanotube Fiber Sensors: Experimental Results and Validation



Laminated composite materials are susceptible to catastrophic failure due to their relatively low interlaminar mechanical properties and poor resistance to low-velocity impact loading. This is heightened by the fact that it is not easy to detect the damage caused by such loading at the onset as it is most commonly likely to occur at interlaminate locations that are not easy to observe on the surface. The purpose of this research is to study this damage as it evolves and propagates through the laminated composite material and monitor its progression. Carbon nanotube (CNT) yarns are integrated into laminated composite materials and used as a sensing mechanism. CNT yarns with their unique piezoresistive property, can measure the change in the resistance of the materials under strain without altering the innate properties or integrity of the laminated composite material. Strain or damage in close proximity to the CNT yarn alters its electrical properties and the change in its resistance measurement could be used to detect and monitor the damage. This paper includes the experimental results of a study about the precise detection of delamination and its evolution in laminated polymeric composite materials using CNT yarn sensors. The experimental results are presented for glass/epoxy laminated composites and include the mechanical loading data of the samples and the electrical resistance data of the CNT yarn sensors. A combination of sensor configurations including CNT yarns stitched through the thickness direction of the composite laminate and CNT yarns placed straight cross wide to the laminate are used to detect the presence of damage as well as its extent and propagation pattern. The results corresponding to a sample implemented with these integrated sensors demonstrate their ability to detect the damage and provide its location as a function of the applied load and in real time. In order to validate the observations from the integrated CNT yarn sensors, x-ray tomography images of the tested samples are used to provide the exact locations of the damage areas and thus corroborate the readings from the CNT yarn sensors.

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