Enhancement of interfacial strength in drilled fiber metal laminates via additive manufacturing techniques

Fiber Metal Laminates (FMLs) are hybrid materials composed of alternating metallic sheets and fiber-reinforced polymer layers, combining high mechanical performance with reduced structural weight. These characteristics make FMLs attractive for structural applications in sectors such as aerospace and transportation. However, their heterogeneous architecture introduces significant challenges during manufacturing operations, particularly drilling, which remains unavoidable for mechanical assembly. Among these challenges, drilling-induced interfacial delamination represents a critical issue, as it can compromise both structural integrity and joint reliability. This thesis investigates drilling-induced delamination in magnesium-based thermoplastic FMLs, with a specific focus on the role of interfacial bonding strength in governing the laminate response under drilling loads. To this end, an interface-engineering strategy is proposed, consisting of the introduction of an additional thermoplastic interlayer based on polyamide 6 (PA6) between the AZ31B magnesium alloy sheet and the fiber-reinforced prepreg. Experimental activities include the manufacturing of FML specimens with and without the additional thermoplastic interlayer, followed by drilling tests performed using different drill geometries. The drilling behavior of the laminates is evaluated through force–stroke measurements and qualitative assessment of drilling-induced damage at both entrance and exit interfaces. Complementary observations are conducted to examine interfacial characteristics and damage distribution. The objective of this work is to assess how the introduction of a thermoplastic interlayer influences interfacial behavior and drilling performance in magnesium-based FMLs, providing insight into interface-driven strategies for improving damage tolerance during machining operations.