Multi-layered controllable stiffness beams for morphing: energy, actuation force, andmaterial strain considerations

Abstract

Morphing aerospace structures could benefit from the ability of structural elements totransition from a stiff load-bearing state to a relatively compliant state that can undergolarge deformation at low actuation cost. The present paper focuses on multi-layered beamswith controllable flexural stiffness—comprising polymer layers affixed to the surfaces of abase beam and cover layers, in turn, affixed to the surfaces of the polymer layers. Heatingthe polymer through the glass transition reduces its shear modulus, decouples the coverlayers from the base beam and reduces the overall flexural stiffness. Althoughthe stiffness and actuation force required to bend the beam reduce, the energyrequired to heat the polymer layer must also be considered. Results show that forbeams with low slenderness ratios, relatively thick polymer layers, and cover layerswhose extensional stiffness is high, the decoupling of the cover layers throughsoftening of the polymer layers can result in flexural stiffness reductions of over 95%.The energy savings are also highest for these configurations, and will increase asthe deformation of the beam increases. The decoupling of the cover layers fromthe base beam through the softening of the polymer reduces the axial strainsin the cover layers significantly; otherwise material failure would prevent largedeformation. Results show that when the polymer layer is stiff, the cover layers are thedominant contributors to the total energy in the beam, and the energy in the polymerlayers is predominantly axial strain energy. When the polymer layers are softenedthe energy in the cover layers is a small contributor to the total energy which isdominated by energy in the base beam and shear strain energy in the polymer layer.