A few notable problems with mechanical actuators include the tendency of systems to overheat, move in constrained/stiff axis and minimum size limitations. Over the summer, I've had to opportunity to explore the field of nanocomposites to look for potential solutions to mechanical actuation in response to thermal or electrical inputs. Along with the National Research Council of Canada, I had the opportunity to support the University of Toronto on their development of smart materials as a potential solution to the aforementioned problems.
Smart materials are a class of materials that have the ability to respond to external stimuli in a pre-programmed manner. An example of this response is physical deformation by the control of stress concentrations in the geometry of samples. I spent a portion of my research term investigating the materials that could be used for electrothermal actuators and ended up modelling the behavior of Carbon Nanotube (CNT) - Polymer composites. To achieve this, I taught myself how to run parametric simulations using ANSYS to model how the changes in material properties influence the deformation characteristics of the beam.
My initial goal was to develop an accurate model that predicted the deformation of a bilayer material consisting of a stiff carbon nanotube buckypaper and a soft polymer layer. A modification of Stoney's Equation was attempted in order to evaluate how the differences in thermal expansion influence the strain rate as a function of temperature but the solution was highly involved. Instead, I modelled these responses using ANSYS Mechanical to attain the following response:
This is a screen-shot of the bi-layer beams response to an input change in temperature. An interesting observation that was made during this analysis was that by simply restraining the elastomer and by controlling the boundary conditions. This property is evident in the plot below, illustrating 4 unique boundary conditions. Control of these conditions as well as the material properties of the bilayer structure can not only modify the direction of deflection, but also the onset of deflection as a function of the temperature. Further development and control on the boundary conditions would allow us to better control the beams response to external stimuli insofar as to aid the development of electrothermal actuators.
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