SIMPLE FRICTION MODEL FOR SCISSOR-TYPE MOBILE STRUCTURES

Mobile or articulated structures have kinematic connections that permit large relative displacements between components that undergo small elastic deformations. Deployable structures are one example. They can be stored in a compact, folded configuration and can be deployed into a load-bearing, open form by simple articulation. The deployable structures investigated in this paper are assemblages of basic units consisting of two straight bars connected to each other by a pivot that are called scissor-like-elements. These structures are stress free and stable in both their folded and deployed configurations, but exhibit a geometrically nonlinear behavior during deployment and dismantling. This behavior is influenced significantly by friction between the bars of each scissor-like-element as they experience a relative rotation about the pivotal connection. Because of the highly nonlinear nature of the structural response, modeling of the problem with contact-type finite elements is not only very expensive, but also of doubtful convergence. Therefore, a simple model is proposed, based on simulating the effect of friction by adding nonlinear rotational springs at the pivotal connections. Numerical results obtained from this model were found to be in very good agreement with experimental measurements.