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Embedded sensors are being explored to non-intrusively monitor the loading experienced by a part either during the manufacturing process or in subsequent service. With the advancement of additive manufacturing techniques, it may be possible to print sensors directly into a part fabricated from metals, polymers, or composites. There is even more benefit if the sensor is also an integral part of the assembly. Single-walled carbon nanotubes and multi-walled carbon nanotubes are used to improve the stiffness and strength of polymeric resins. But they also offer an additional benefit of reversible piezo-resistive behavior. The objective of this study was to explore the fidelity of a signal extracted from nanocomposite samples of multi-walled carbon nanotube/epoxy resin under uniaxial loading, as a function of increasing content of multi-walled carbon nanotube. Data obtained from the multi-walled carbon nanotube networks formed correlated with the strain as a function of the mechanical loading. The gauge factors calculated for the multi-walled carbon nanotube/epoxy samples ranged from 2.651 to 5.064 as compared to the metallic strain gauge factor of 2.125 used to calibrate the samples. Under repeated mechanical loading, the initial zero-strain condition was recovered within 5 min after unloading. In samples with 5 wt% of multi-walled carbon nanotubes, the electrical conductivity and gauge factor plateaued. Furthermore, increases in the w/w% of multi-walled carbon nanotube resulted in degradation of the mechanical properties of the multi-walled carbon nanotube/epoxy resin.

Polymeric composite laminates play a vital role in the fabrication of strong, lightweight materials. Composites also play a critical role in the aerospace and automotive industries. They are the very things that protect us from harsh environments. Due to widespread usage, it is important to understand how these materials age and perform over time. The advantages of polymeric composites are high rigidity, high strength to weight ratio, corrosion resistance, high fatigue strength, low thermal expansion, and manufacturability. The advantages of polymeric composite parts in machines and vehicles are low mass, high speed of operation, excellent fatigue resistance, quiet running due to shock absorption, easy installment and demounting, low maintenance cost, low energy costs during production and life cycle. Despite the advantages, there are concerns regarding the long-term durability of these composites especially when it comes to performances under critical and varying conditions. Since Terfenol-D, a magnetostrictive material will be placed in these polymeric composites for structural health monitoring, it is imperative to understand the microstructure of the particles and their net effect on the resin, e.g. distortions, volume fraction, and induced strain. Terfenol-D (Tb1−xDyxFe2) is of the cubic laves phase structure in which there is less plastic deformation which in turn makes the particles hard and brittle.