Bill Armstrong memorial session: elastic modulus and strain recovery testing of variable stiffness composites for structural reconfiguration applications

Abstract

ABSTRACT Morphing structures have the potential to significantly improve vehicle performance over existing fixed component designs. In this paper, we examine new composite material design approaches to provide combined high stiffness and large reversible deformation. These composites employ shape memory polymers (SMP) matrices combined with segmented metallic reinforcement to create materials with va riable stiffness properties an d reversible accommodation of relatively large strains. By adjusting the temperature of the sample, the storage modulus can be varied up to 200x. We demonstrate the segmented composite concept in prototype materials made using thermoplastic polyurethane SMP reinforced with interlocking segmented steel platelets. Measured storage moduli varied from 5-12 GPa, below SMP T g , and 0.1-0.5 GPa above SMP T g . The samples demonstrated more than 95% recovery from induced axial strains of 5% at 80°C. Viscoelastic effects are dominant in this regime and we investigate the rate dependence of strain recovery. Keywords: morphing, variable stiffness materials, shape memory polymer, reconfigurable surface, strain recovery, segmented composite