Braided reinforcements in orbiting bodies: The effect of UV photodegradation on the tensile properties of 2D tubular braided composites intended for space applications

The high specific stiffness, damage tolerance, and tailorable thermal expansion of tubular braided composites (TBCs) render them attractive options for lightweight space structures. Research into the durability of TBCs under space-relevant ultraviolet spectra remains limited. This study is the first to examine the effect of AM0 ultraviolet, visible, and near-infrared radiation (350–1200 nm) on tensile behaviour of carbon/epoxy and Kevlar®/epoxy 2D TBCs. Specimens were manufactured at three braid angles (35°, 45° and 55°) and exposed to 0 and 14 days (∼336 h) of continuous low Earth orbit irradiance, with mass measured at 0, 7, and 14 days, followed by tensile tests to determine mechanical properties. Carbon/epoxy TBCs showed negligible mass change (±0.1%), implying ultraviolet damage was confined to a thin epoxy surface layer. Carbon 45° and 55° TBCs exhibited increases in tensile modulus (up to 76%) and UTS (up to 46%) with reduced yield strain, indicating ultraviolet-induced stiffening and embrittlement of the matrix and fibre–matrix interface. Kevlar®/epoxy TBCs lost approximately 1% of their initial mass and developed surface discolouration. Kevlar 35° TBCs showed significant increases in modulus (∼10%) and yield strength (∼14%) yet the yield strain and UTS did not change. Kevlar 45° and Kevlar 55° showed no tensile changes, supporting a self-screening mechanism. Overall, AM0 exposure increases stiffness and tensile strength while reducing deformation capacity in carbon TBCs, whereas Kevlar® TBCs exhibit smaller, braid-angle dependent tensile changes, highlighting the importance of fibre type and braid architecture in the implementation of UV-exposed braided composite components for space applications.