1. Development of novel hybrid TPMS cellular lattices and their mechanical characterisationNejc Novak, Oraib Al-Ketan, Matej Borovinšek, Lovre Krstulović-Opara, Reza Rowshan, Matej Vesenjak, Zoran Ren, 2021, original scientific article Abstract: Uniform lattices composed of one type of lattice structure repeated periodically have been extensively investigated in literature for their mechanical and physical properties. Their promising properties, which include a desirable combination of high strength, stiffness and toughness, suggest that hybrid structures made of two or more lattice types can exhibit even more advantageous and desired properties. In this work, the mechanical properties of hybrid cellular structures designed using implicit functions are investigated both experimentally and numerically. Two proposed samples are investigated comprised of a Gyroid and a Diamond unit cells hybridised linearly and radially. First, a finite element computational model was utilised in LS-DYNA to capture the mechanical properties of the additively manufactured constituent lattices (i.e., Gyroid and Diamond) made of stainless steel 316L and tested under dynamic and quasi-static loading conditions. The model was validated for three different relative densities. Then, the validated computational model was then tested to predict the mechanical behaviour of the proposed hybrid lattices. Finally, the proposed hybrid lattices were fabricated and mechanically tested to obtain their mechanical properties. A good agreement between experimental and computational results was achieved. The validated computational models will be used to evaluate other designs of TPMS lattices and their crashworthiness performance for protective equipment applications.
Keywords: cellular materials, triply periodical minimal surface, hybrid lattices, experimental testing, computational modelling, multi-morphology
Published in DKUM: 27.11.2024; Views: 3; Downloads: 0
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2. Mechanical behaviour of photopolymer cell-size graded triply periodic minimal surface structures at different deformation ratesYunus Emre Yilmaz, Nejc Novak, Oraib Al-Ketan, Hacer Irem Erten, Ulas Yaman, Anja Mauko, Matej Borovinšek, Miran Ulbin, Matej Vesenjak, Zoran Ren, 2024, original scientific article Abstract: This study investigates how varying cell size affects the mechanical behaviour of photopolymer Triply Periodic Minimal Surfaces (TPMS) under different deformation rates. Diamond, Gyroid, and Primitive TPMS structures with spatially graded cell sizes were tested. Quasi-static experiments measured boundary forces, representing material behaviour, inertia, and deformation mechanisms. Separate studies explored the base material’s behaviour and its response to strain rate, revealing a strength increase with rising strain rate. Ten compression tests identified a critical strain rate of 0.7 s−1 for “Grey Pro” material, indicating a shift in failure susceptibility. X-ray tomography, camera recording, and image correlation techniques observed cell connectivity and non-uniform deformation in TPMS structures. Regions exceeding the critical rate fractured earlier. In Primitive structures, stiffness differences caused collapse after densification of smaller cells at lower rates. The study found increasing collapse initiation stress, plateau stress, densification strain, and specific energy absorption with higher deformation rates below the critical rate for all TPMS structures. However, cell-size graded Primitive structures showed a significant reduction in plateau and specific energy absorption at a 500 mm/min rate.
Keywords: cellular materials, triply periodical minimal surface, photopolymer, mechanical properties, strain rate, experimental compressive testing, computer simulations
Published in DKUM: 22.05.2024; Views: 216; Downloads: 15
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