Developing thermoplastic hybrid titanium composite laminates (HTCLS) at room temperature: Low-velocity impact analyses

Abstract

Hybrid titanium composite laminates (HTCLs) are high-performance light-weight fiber metal laminates (FMLs) that are being increasingly used in various industries such as aeronautical, military, and marine thanks to their optimized fracture toughness, impact resistance, and thermal performance. In the current study, the low-velocity impact (LVI) characteristics of a new generation of thermoplastic (TP) HTCLs at various energy levels are investigated. To do so, Ti-6Al-4 V sheets, carbon fabrics, and ultra-high molecular weight polyethylene (UHMWPE) fabrics are used to fabricate multiple laminates with different fiber types, metal volume fractions, and lamination layups. A low-cost resin infusion process is employed for manufacturing the laminates at room temperature by using a novel liquid thermoplastic methyl methacrylate resin, Elium® 188. Before fabrication, a multi-step surface treatment method is applied on Ti alloy sheets to enhance the interfacial properties between the composite layer and the metal alloy sheet. In addition to TP-HTCLs, equivalent thermosetting (TS) HTCLs with an epoxy resin, Epolam, are fabricated to compare the results and evaluate the possibility of fabricating recyclable TP-FMLs at room temperature with enhanced out-of-plane properties. Impact properties including contact force, deflection, energy parameters, and related damage modes are investigated and presented for each laminate. It is concluded that the newly developed TP-HTCLs can be cured at room temperature and have enhanced impact properties compared to those of TS-HTCLs. Besides, the HTCL with UHMWPE fabrics on its composite sides (before the Ti alloy sheets) performs better in LVI compared to that with carbon fibers on the top and bottom (of its composite core) since UHMWPE exhibits higher strain to failure and fracture toughness compared to carbon fibers.