Stress and Cure Sensing of Single-Shape Memory Alloy (SMA) Fiber/Epoxy Composites using Electro-micromechanical Technique

SMA (shape memory alloy) is well known to change the microstructure from martensite to austenite with either temperature or stress. Stress and temperature response were investigated for SMA fiber/epoxy composites using an electro-micromechanical technique during curing. SMA fiber can be used in practical applications, including stress or cure-monitoring sensors, due to its inherent shape recovery properties, i.e., it exhibits a shape memory effect (SME) when subjected to applied stress or temperature. Superelasticity was observed for SMA fiber/epoxy composites under cyclic stress–strain curve. Under a certain stress, the original modulus was reduced steeply but then recovered under further stress. A sudden transitional change in electrical resistance was also observed around 87°C with an increase of temperature. Under cyclic loading the stress was suddenly leveled-off with a certain stress, which resulted in a different stress hysteresis repeatedly with two differing matrices and surface treatment. In SMA fiber/epoxy composites, residual stress of single-SMA fiber with and without embedding epoxy matrix exhibited the incomplete and complete recovery, respectively, during the curing process. Interfacial effect between SMA fiber and matrix can be important factor for practical applications including feasible sensing and actuator.