Design and Testing of a Variable Stiffness Honeycomb Composite

Abstract

Abstract Shape Memory Polymer (SMPs) have been of interest for use in morphing structures. Owing to their low cost and density, large stiffness change in excess of 1000X, and easy tailorability, they are an attractive option as a variable stiffness material and in variable stiffness structures. One limitation of these polymers, however, is that they are generally too compliant for high force applications, with maximum moduli less than 3 GPa. It is of interest then to develop methods to increase the modulus of these materials while preserving their stiffness change. In this research a novel multimaterial smart carbon fiber honeycomb is designed as a reinforcement for a styrene SMP infill, creating a variable modulus honeycomb composite. A unit cell finite element model is created, and parametric studies are completed to explore the design space of the composite. Selected cell geometries are fabricated and tested to validate the fabrication method and determine their the in-plane effective modulus, Poisson’s ratio, and stiffness change through SMP activation. The results find increases in modulus over the SMP alone of up to 400%, and modulus close to those of the SMP are found to be possible. Modulus changes of nearly 450X are demonstrated, which is found to be an underprediction owing to experimental uncertainty. The predicted and measured performance of this type of composite, along with the ease of tailoring the cell geometry, represent a potentially attractive option for variable stiffness SMP composites and morphing structures.