Beams with controllable flexural stiffness

Abstract

This paper describes a method to vary the flexural bending stiffness of a multi-layered beam. The multi-layered beam comprises a base layer with polymer layers on the upper and lower surfaces, and stiff cover layers. Flexural stiffness variation is based on the concept that when the polymer layer is stiff, the cover layers are strongly coupled to the base beam and the entire multi-layered beam bends as an integral unit. In effect, we have a 'thick' beam with contributions from all layers to the flexural bending stiffness. On the other hand, if the shear modulus of the polymer layers is reduced, the polymer layers shear as the base beam undergoes flexural bending, the cover layers are largely decoupled from the base, and the overall flexural bending stiffness correspondingly reduces. The shear modulus of the polymer layer is reduced by increasing its temperature through the glass transition. This is accomplished by using embedded ultra-thin electric heating blankets. From experiments conducted using two different polymer materials, polymer layer thicknesses and beam lengths, the flexural stiffness of the multi-layered beam at low temperature was observed to be between two and four times greater than that at high temperature.