Active Tuning of Variable Stiffness Structures Utilizing Fluidic Flexible Matrix Composites

Active tuning of a variable stiffness structure utilizing fluidic flexible matrix composites (F²MC) through valve control is investigated in this research. Previous efforts have shown that significant changes in the effective modulus of elasticity can be achieved by simply opening and closing the inlet valve to the fluid filled F²MC tubes. Through integration of the F²MC tubes into supporting matrix materials, multicellular variable stiffness adaptive structures can be achieved. The new adaptive structures can be easily deformed when desired (open valve) and can be switched to a high modulus mode when deformation is not desired (closed valve – locked state). In this paper, active valve control is investigated for improving the performance of the variable modulus structure over the semi-active approach (on/off valve control). An analytical model of the fluid-filled F²MC tube is developed that captures the dynamics of the composite tube and the flow rate of the fluid through a variable orifice. A feedback controller for modulus tuning is determined. Analysis results indicate that the modulus of the structure can be accurately tuned by active valve control. Advantages over semi-active valve control are increased performance, greater control of modulus selection, increased applicability, and elimination of potentially damaging pressure spikes observed with on/off valve control.