Abstract
Additive manufacturing (AM) enables the fabrication of complex, lightweight, and architecturally optimized lattice scaffolds with tunable mechanical and biological properties. Among these, Ti6Al4V-based triply periodic minimal surface (TPMS) structures are particularly promising for orthopedic applications due to their bone-mimetic geometry, mechanical compatibility, and interconnected porosity. This thesis tests the hypothesis that topologically tailored, and fatigue-informed lattice designs can significantly enhance AM scaffolds' structural integrity and biological viability in fatigue-prone biomedical and engineering environments, especially under complex multiaxial loading conditions. However, the fatigue behavior of such structures remains insufficiently understood, limiting their widespread clinical and industrial application. Moreover, the influence of lattice architecture, process-induced defects, and post-processing on fatigue life prediction is inadequately captured by current design methodologies. Combining experimental, numerical, and validated analytical approaches across five peer-reviewed studies, this cumulative dissertation addresses these challenges through an integrated exploration of fatigue simulation, mechanical testing, and advanced scaffold design. The first review paper presents a systematic taxonomy of fatigue simulation strategies in metal AM, emphasizing the need for defect-sensitive and multiscale modeling frameworks. The second review synthesizes architected lattices' mechanical, fatigue, and osseointegration performance, establishing structure-property–function relationships across TPMS, strut-based, stochastic, and graded configurations. The third experimental study investigates the quasi-static and fully reversed high-cycle fatigue (R = –1) behavior of gyroid and diamond TPMS lattices, demonstrating improved fatigue limits of 50 MPa and 83 MPa, respectively, following heat treatment and hot isostatic pressing. The fourth paper introduces a multidirectional functionally graded (MDFG) scaffold inspired by bone architecture, in which gyroid, primitive, kelvin, and Voronoi lattices were strategically distributed along three spatial directions to achieve compressive strength up to 240 MPa, energy absorption of 47.7 MJ/m³, and fatigue strength of 25 MPa at 10⁶ cycles. The final study evaluates TPMS scaffold durability under realistic service conditions using strain-controlled multiaxial low-cycle fatigue (LCF) loading conditions with combined axial–torsional loading—an approach closely reflecting physiological and engineering load cases. The work highlights topology-dependent fatigue life and cyclic behavior. It validates fatigue predictions through Brown–Miller, Fatemi–Socie, and energy- based models, offering direct insights for designing implants and components exposed to complex multiaxial stresses. Collectively, these studies provide a comprehensive framework for fatigue-informed lattice design in AM, supporting the development of next-generation biomedical implants and structurally demanding engineering components. The outcomes bridge materials science, structural mechanics, and biomedical engineering disciplines advancing scientific understanding and real-world application readiness.