Hybrid composite tubes under torsion: natural versus synthetic fiber performance

Introduction: Although composite materials have been studied and validated through several tests, research on torsional behavior in tubular structures remains limited. Tubular configurations are common in diverse engineering fields, and composites, particularly those reinforced with synthetic and natural fibers, hold promise for advancing technology by offering a combination of good strength and low density. In this context, the main objective of this work is to compare the torsional behavior of laminated composite and hybrid (aluminum/composites) tubes. Materials and methods: In this study, prepregs were manufactured by hand lay-up using fibers and epoxy with different numbers of layers and fiber angle dispositions, maintaining a 30% volume fraction. The specimens were fabricated using the roll-wrap method, in which prepregs were manually wound onto tubular molds, obtaining the following configurations: sisal4 [45°]/epoxy, glass2 [45°]/epoxy, sisal2 [0°]/epoxy/Al, and glass:aramid [0°]/epoxy/Al. Sisal fiber was pretreated with 5% (w/v) sodium hydroxide (NaOH) to enhance adhesion to the matrix. Subsequently, the specimens were subjected to thermal analysis and torsional tests. Results: The results indicate that the glass:aramid [0°]/epoxy laminate, after curing, exhibited higher thermal stability (343.24 °C) than the cured sisal2 [0°]/epoxy laminate (322.82 °C). The degree of cure was essentially the same for both systems, although the glass:aramid [0°]/epoxy sample showed a slightly higher degree of cure (98.57%) than the sisal2 [0°]/epoxy sample. In addition, the sisal2 [0°]/epoxy/Al specimen under torsional loading reached a higher torque (19.65 N·m) than the glass:aramid [0°]/epoxy/Al specimen (17.98 N·m). Conclusions: The hybrid composites exhibited superior properties compared to sisal4 [45°]/epoxy and glass2 [45°]/epoxy composite tubes. Nonetheless, sisal fiber shows potential as a substitute for synthetic fibers in select projects, contingent on specific performance criteria.