Active dynamic response tuning of adaptive composites utilizing embedded nitinol actuators

Adaptive composites utilizing embedded nitinol fibers have the unique ability to change their material properties, induce large internal distributed forces in a structure, and can modify the stress and strain distribution within a structure in a controlled manner. In this study, nitinol fibers are embedded in graphite-epoxy and are used as distributed actuators to actively tune the dynamic response of clamped-clamped beams. The natural frequencies of clamped-clamped nitinol composite beams are shown, experimentally. to increase linearly as a function of temperature. Beams with nitinol volume fractions of 5% 10%, and 15% can increase their first natural frequency by factors of 1.7, 2.5, and 3.0 respectively.

Classical lamination theory is used to formulate a mathematical model of the dynamic response which includes the adaptive properties of the embedded nitinol fibers as a function of temperature, as well as the thermal aspects of the matrix material. Experimental characterization of nitinol for use as constrained thermosets is performed and the results are used in the mathematical model. The mathematical model is used to calculate the natural frequencies of clamped-clamped nitinol composite beams and the results are compared to experimental results.

It is clear that adaptive composites represent a new concept in active control of structural responses and may act as a catalyst for future developments in both material and structures technology. Demonstrating, experimentally and computationally, the ability to alter the dynamic response using unique adaptive qualities will hopefully inspire new material/structural interaction paradigms.