Modeling, design, and experimental testing of integrated fluidic flexible matrix composite structures

Fluidic Flexible Matrix Composites (F2MCs) consist of a highly anisotropic FMC laminate that encloses a working fluid. The FMC laminate is basically a composite shell that has reinforcements orientated at a particular angle with respect to the longitudinal axis. F2MC tubes have been shown to provide actuation, stiffness change, and vibration reduction in applications that require isolated tubes or multiple tubes embedded in a soft matrix. Structural applications, however, often require stiff and strong materials. The objective of this research is to integrate relatively soft F2MC tubes into rigid host structures, by either embedding or bonding, such that the F2MC integrated structures can have tunable shape, stiffness, fluid pumping, vibration damping, or vibration absorption characteristics.;First, we explore the functionality of F2MC tubes embedded into a stiff matrix. The geometry and anisotropy of the tube can be tailored for either highly leveraged fluid pumping under mechanical deformation or highly leveraged stiffness change by preventing fluid flow into or out of the tube. A bilayer analytical model is developed using Lekhnitskii's solution for an anisotropic tube under axial and pressure loading. The analysis shows a confining effect of the surrounding rigid matrix on the performance of F2MC tubes. With tailoring of the tube wall thickness (thick) and wind angle (near-axial), however, F2MC tubes can pump 250 times more fluid than a piston of the same diameter. Furthermore, axial stiffness can be increased by a factor of 2.2 when fluid flow is prevented.;Secondly, the actuation performance of F2MC tubes embedded in structural media is investigated. The unit cell models examined are cylindrical and bi-layer with the inner layer being a thick walled F2MC tube and the outer layer representing the surrounding rigid composite and composed of either homogeneous epoxy or a second FMC layer made with stiffer matrix material. The analytical models are validated using ABAQUS. The analytical results show that actuation performance is generally reduced compared to that of an isolated F2MC tube due to the radial and longitudinal constraints. Free strain is generally two orders of magnitude smaller for an F2MC tube in structural media, requiring higher actuation pressures for bi-layer F2MC structures. The blocking force of F2MC in either epoxy or composite is roughly an order of magnitude smaller than that of an isolated F2MC tube.;Thirdly, we propose damping the vibration of a cantilever beam by bonding multiple F2MC tubes to the beam and using the strain induced fluid pumping to dissipate energy. Transverse beam vibration strains the F 2MC tube and generates fluid flow through an energy dissipating orifice. An optimally sized orifice maximizes energy dissipation, greatly reducing the resonant peaks and increasing modal damping. An analytical model is developed based on Euler-Bernoulli beam theory and Lekhnitskii's solution for anisotropic layered tubes. Using miniature tubes, a laboratory-scale F 2MC-integrated beam prototype is constructed and experimentally tested. The experimental results agree well with the theoretical predictions, provided the fluid bulk modulus is reduced to reflect the entrained air in the fluidic circuit. A design space study shows that damping ratios of 32% and 16% are achievable in the first and second modes of a cantilever beam, respectively, using an F2MC damping treatment.;Finally, this research shows that F2MC tubes with resonant fluidic circuits can absorb and isolate vibration at a specific frequency when bonded to flexible structures. The transverse structural vibration applies cyclic axial strain to the F2MC tubes. The anisotropic elastic properties of the composite tube amplify the axial strain to produce fluid flow through a flow port and into an accumulator. The fluid inertance in the flow port (inertia track) and the stiffness of the accumulator are analogous to the vibration absorbing mass and stiffness in a conventional tuned vibration absorber or isolator. The collocated tip force to tip displacement analytical transfer function of the coupled system is derived for the vibration absorber analysis. For vibration isolation analysis, the tip force to base shear and moment transfer functions are derived. Experimental testing is conducted on a laboratory-scale F2MC beam structure. The resonant peak becomes an absorber notch in the frequency response function if the inertia track length is properly tuned. Tuning the fluid bulk modulus and total flow resistance in the theoretical model produces results that match the experiment well, predicting a magnitude reduction of 35 dB at the first resonance using an F2MC absorber. Based on the experimentally validated model, analysis results show that the cantilever beam vibration can be reduced by more than 99% with optimally designed tube attachment points and flow port geometry. The model also predicts 99.3% reduction of transmitted forces and moments from the tip force. For a given fluidic circuit design, however, the absorber, shear isolation, and moment isolation frequencies are different.