Visualising Compliance of Composite Shell Mechanisms

Abstract

In the design of isotropic compliant shell-based mechanisms a desired response of an end-effector is commonly achieved through careful selection of shell geometry and material. However, for applications such as the design of medical support devices the shell must conform to a highly constrained set of permissible geometries, limiting tailorability. One solution to this design challenge is to exploit anisotropic material behaviour. Advanced composite materials may be elastically tailored by varying the fibre orientation, but at the cost of increased design complexity. Herein we present an approach for capturing the effects of material anisotropy on compliant shell mechanisms by providing the designer with a method for visualising their response in a physically intuitive manner. We extend the mechanism characterisation technique of Lip-kin and Patterson [1] using eigen-decomposition, and visualise the compliance vectors for structures with material anisotropy. We characterise the behaviour of cantilevered “tape-spring” shell geometries with varying enclosed angles using nonlinear finite element analysis. For small enclosed angles we observe significant reorienting of the compliance vectors due to stiffness anisotropy; as the enclosed angle is increased, geometry dominates the response. However, in an intermediate region both geometric and stiffness effects interact, highlighting the potential richness of the design space.