Effects of laser-textured groove geometry on interfacial bonding in titanium-based thermoplastic fiber metal laminates

Fiber metal laminates are increasingly used in lightweight structures, but interfacial delamination arising from the mismatch between dissimilar layers remains a major reliability concern. Laser texturing can improve metal–polymer bonding through enhanced wettability and mechanical interlocking, yet the resulting surface geometry is still treated as an empirical descriptor of the treatment rather than as a variable of the interfacial response. In this study, the interfacial behavior of Ti6Al4V/PA6-based thermoplastic FMLs was investigated experimentally and numerically. Oriented microgrooves with distinct morphologies were produced by varying the laser texturing parameters, and the normal and shear interfacial strengths were evaluated through normal-separation and single-lap-shear tests, supported by SEM and EDS observations of the delaminated surfaces. Within the investigated processing range, lower scanning speeds produced larger effective groove-wall slopes, accompanied by a transition from metal–polymer adhesive failure toward polymer cohesive and prepreg-involved substrate failure and by increases in both normal and shear strength. A mechanics-based analysis showed that the groove-wall slope governs the partitioning of displacement and traction into components normal and parallel to the groove walls, and hence the effective interface stiffness. The measured arithmetic mean slope was therefore incorporated into a geometry-dependent traction–separation formulation and implemented in a cohesive-zone model. Calibrated exclusively on the two pure-mode tests, the model reproduced both the force–displacement response and the geometry-dependent delamination initiation and propagation measured in double cantilever beam tests, providing an independent validation under mixed-mode loading.