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Mechanical-electrical properties and failure behavior of 3D printed carbon fiber reinforced composites with multiwalled carbon nanotube (MWCNT)/ waterborne polyurethane (WPU) conductive coating were studied to develop a performance monitoring method for composites. The results indicated that the coating materials could obtain good mechanical-electrical properties and sensitivity factor. Scanning electron microscopy images show that multiple conductive channels exist in the coating. The coating is well bonded to the composites. In order to obtain more details, mechanical-electrical coupling simulation was conducted. The experiment and simulation are in good agreement. The correlation between the strain of composite part and the electrical resistance change rate of the coating is validated. Furthermore, the multi-scale observations reveal the failure mechanism including composite-coating debonding, brittle fracture of polyamide matrix, fiber breakage, and pull-out in the composite part, as well as ductile fracture of WPU matrix and MWCNT pull-out in the coating part. This study can provide some insights for structural health monitoring of composites.

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With the wide application of carbon fiber reinforced polymer (CFRP) composites, dynamic loading cases are increasingly considered in structural design and analysis. Hence, it is necessary to investigate their dynamic mechanical properties. In this paper, the carbon/epoxy laminates with different stacking sequences prepared by vacuum assisted resin infusion process were studied by quasi-static tension and split Hopkinson tension bar experiments. The loading strain rate is ranged from 2.2 × 10−4 s−1 to 2200 s−1. The results indicate that the composites are strain rate dependent. Four stacking sequence laminates show different strain rate sensitivities, and their mechanical performance differences depend on the strain rate. As the strain rate increases, tensile strength and elastic modulus increase, but failure strain decreases. Therein, the elastic modulus is highly sensitive. The elastic modulus difference of unidirection/cross-ply or unidirection/quasi-isotropic decreases but that of unidirection/angle-ply increases with increasing strain rate. The failure strain difference of unidirection/angle-ply decreases significantly with increasing strain rate. These experimental data and research results could provide some insight for epoxy matrix CFRPs.