Actuation of flu id ic flexible matrix composites in structural media

摘要

Fluidic flexible matrix composite (F~2MC) tubes have been shown to provide actuation and stiffness change in applications that require isolated tubes or multiple tubes embedded in a soft matrix. Structural applications often require stiff and strong composites, however, so this article addresses the actuation performance of F~2MC tubes embedded in structural media. Two analytical models are developed based on Lekhnitskii's solutions for a homogeneous orthotropic cylinder with axial force and pressure loading. These unit cell models are cylindrical and bilayer with the inner layer being a thick-walled F~2MC tube and the outer layer representing the surrounding rigid composite and are composed of either homogeneous epoxy or a second FMC layer made with stiffer matrix material. The models are validated using ABAQUS. Free strain and blocked force are calculated for a variety of unit cell designs. The analytical results show that actuation performance is generally reduced compared to that of an isolated F~2MC tube due to the radial and longitudinal constraints imposed by the surrounding structural medium. The free strain is generally two orders of magnitude smaller for an F~2MC tube in structural media, requiring higher actuation pressures for bilayer F~2MC structures. The blocking force of F~2MC in either epoxy or composite is roughly an order of magnitude smaller than that of an isolated F~2MC tube. The analysis shows a great degree of tailorability in actuation properties, so that the F~2MC tube can be designed to minimize these differences. Higher actuation performance is achieved, for example, with a thick-walled F~2MC tube, as opposed to the thin wall that maximizes performance in an isolated F~2MC tube.