Evaluation of Millimeter-Size Fluidic Flexible Matrix Composite Tubes

Fluidic flexible matrix composite (F²MC) tubes are fiber-reinforced tubes that have been designed to change structural characteristics (e.g., shape, stiffness, damping, actuation force, etc.) based on the control of fluid flow and pressure inside the tubes. In the current investigation, miniature F²MC tubes (2 mm diameter) are designed and evaluated. The tubes are made with fine steel wire and a flexible polyurethane matrix. Tubes with reinforcement angles of ±40 and ±24 degrees relative to the longitudinal axis were evaluated in terms of blocked force and free strain versus internal pressure and axial modulus of elasticity. Sheets of multiple, unidirectionally aligned tubes positioned side by side and potted into a surrounding compliant matrix material were evaluated as well. Encouraging agreement with elasticity solutions based on infinitely long multi-layer tubes with internal pressurization was observed. Over the long term, this line of research is aimed at the development of thin skins for structures that can change shape and stiffness differently as a function of direction.