Fluidic flexible matrix composites for the tailoring of variable stiffness adaptive structures

Fluidic flexible matrix composites (F²MC) are investigated in this research for the tailoring of variable stiffness adaptive structures. By taking advantage of the high anisotropy of flexible matrix composite (FMC) tubes and the high bulk modulus of the pressurizing fluid, significant changes in the effective modulus of elasticity can be achieved by controlling the inlet valve to the fluid filled F²MC tubes. Through integration of the F ²MC tubes into supporting matrix materials, multicellular variable stiffness adaptive structures can be achieved. The new adaptive structures have the flexibility to easily deform when desired (open valve) and possess the high modulus required under loading conditions when deformation is not desired (closed valve - locked state). In this paper, a comprehensive numerical model based upon the finite element method is developed that captures the solid and fluid interaction of the single F²MC tube for the open and closed valve states. Using the finite element analysis results for the single F ²MC tube, a mathematical model of the multicellular variable stiffness structure is created based upon a 'Rule of Mixtures' modeling approach. Experiments are performed to validate the proposed models, and good agreement is observed with the model predictions. Modulus ratios of 25.1 and 21.6 are measured for the single F²MC tube and the multicellular structure, respectively. Parameter studies using the validated finite element models are performed to gain design insight for the variable stiffness structures.