Geometrically-Tailored Lattice Structures with Tunable Mechanical Characteristics Enabled via Additive Manufacturing

Abstract

In today’s world, the focus on compact and advanced systems has driven demand for smart materials such as lattice structures, which offer high weight-specific stiffness, strength, and energy absorption, particularly valuable in aerospace, biomedical, and engineering applications. Despite their advantages, commonly used lattice architectures, such as the pyramidal lattice exhibit bend-dominated behavior, where deformation is primarily governed by strut bending. This results in ineffective load bearing ability and inefficient material utilization, particularly at low relative densities. A viable approach to enhance material utilization in these strut-based lattices is the geometric tailoring of strut cross-sections. State-of-the-art additive manufacturing (AM) techniques have enabled the fabrication of complex structures with fine features, unlocking new potentials to fabricate intricate and sophisticated designs with exceptional mechanical properties. This Ph.D. dissertation introduces a novel design strategy that converts strut profiles into an I-shape, enhancing load-bearing efficiency in bend-dominated lattice networks. Geometrically tailored I-shaped strut pyramidal lattices are 3D printed via Digital Light Processing (DLP) and their mechanical performance is experimentally evaluated under compressive, shear, and impact loading. In addition to experiments, comprehensive non-linear finite element (FE) analyses are performed to examine underlying collapse mechanisms, accurately simulate experimental results, and explore the vast design space offered by the proposed geometrical tailoring scheme. The key findings in this dissertation demonstrate the superior performance of geometrically tailored pyramidal lattices compared to conventional pyramidal lattices of equivalent weight. The tailored lattices under out-of-plane compressive loading exhibit significant increase in elastic modulus (+24%), collapse strength (+34%), and energy absorption (+109%). These noteworthy enhancements are attributed to lateral buckling, which induces sideways bending of the I-shaped struts during collapse, enhancing collapse resistance. Additionally, geometrical tailoring enhances shear resistance, with enhancements in shear modulus (+23%) and shear strength (+16%) through the optimal choice of architectural parameters. This dissertation also introduces the novel concept of incorporating corrugated stiffeners within hexagonal lattices to enhance the lattice performance under quasi-static compression in both in-plane and out-of-plane directions, without altering the overall relative density. The effectiveness of this approach is validated through a comprehensive set of experiments and finite element (FE) simulations, which demonstrate significant enhancements in the elastic modulus (+348%), collapse strength (+192%), and specific energy absorption (+112%) of the architected hexagonal honeycombs compared to traditional hexagonal honeycombs. These findings demonstrate the efficacy of geometrical tailoring scheme as a viable approach in enhancing the mechanical properties of lattice structures, with significant relevance for various applications, including crashworthiness, impact mitigation, armoring protection, and bird strike resistance in the aerospace, automotive and defence sectors.

Date of Award	11 Dec 2024
Original language	American English
Supervisor	Andreas Schiffer (Supervisor)