Amorphous Bonding for In-Space Welding of Thermoplastic Composite Deployable Structures

Abstract To meet the demands for large-scale space structures and overcome the constraints of volume and weight during delivery, stowing segments of a boom and welding in-space offers a possible solution. As a result, thin-ply thermoplastic polymer composites (TPCs) are analyzed in this study for their ability to undergo multiple welding cycles through fusion bonding, which consists of intimate contact, healing, and solidification. Crystallization of TPCs poses a challenge during thermoplastic processing, as it impairs interface healing and requires slow cooling to achieve proper fiber-matrix adhesion, which can be challenging for in-space welding. To address this, a composite material is developed by introducing an amorphous polyetherimide (PEI) sheath layer to the surfaces of a semi-crystalline polyetheretherketone (PEEK) composite. Notably, the sheath is miscible with and healable below the melt temperature of the PEEK, resulting in a thermoplastic composite capable of welding without melting the crystals, forming a “Goldilocks Zone” for structural bonding. This research initiates an exploration for the potential of amorphous bonding for deployable space structures, by presenting a series of material tests. The details of the fabrication of the new thin-ply TPC are discussed and large-curvature Column Bending Test (CBT) results are presented. CBTs are conducted to assess the effect of the additional amorphous PEI layer on bending stiffness, strength, and failure modes in the large-curvature regime. The results show promise for amorphous bonding of deployable segments in-space.