Title: Composite Hinge Structures with Variable In-Plane Stiffness

Authors: Colin Rowbottom, Lauren A. Moore, and Daniel M. Baechle

DOI: 10.33599/nasampe/c.19.0720

Abstract: This paper investigates a lightweight continuous fiber composite hinge structure employing a dual matrix for tailorable bending stiffness with the intended application for exoskeletons and robotics. Incorporating a dual matrix to the structure restricts torsion and in-plane bending, while allowing for localized out-of-plane bending. Classical laminate theory was applied to optimize the design process coupled with a pseudo-rigid-body model to gain insight into mechanical behavior of the hinge structure under various loading conditions prior to experimental testing. The composite lay-up consists of mid-plane layers of continuous woven fabric with alternating regions of epoxy and flexible polyurethane (PU) film, and additional layers of woven carbon fabric in the epoxy sections to increase stiffness. A two-stage fabrication process first bonds the PU film with the flexible fabric of the hinge section and next, applying a vacuum assisted resin transfer molding (VARTM) process, infuses epoxy resin into the remaining mid-plane fabric layers and the outer carbon layers. Experimental testing exhibited damage to carbon fibers in the PU hinge section under high deformation, whereas Kevlar proved to be more robust. Low-cycle fatigue testing demonstrated a decrease in bending and torsion stiffness after the first test cycle, but remained relatively constant thereafter. Using 0/90 fabric in the hinge section resulted in a 160 % increase in out-of-plane bending stiffness over ±45 fabric. Doubling ply count in the hinge section resulted in an expected 2× increase in torsion stiffness, while doubling the sample width resulted in a 12× increase in torsion stiffness. Material design considerations towards exoskeleton and robotics applications will be discussed.

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Conference: CAMX 2019

Publication Date: 2019/09/23

SKU: TP19-0720

Pages: 15

Price: $30.00