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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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Abstract: The study presents an extensive mechanical and computational characterisation of novel cellular metamaterial with axisymmetric chiral structure (ACS) at different strain rates. The Direct Impact Hopkinson Bar (DIHB) testing device was used for impact testing up to 21 m/s striker speed, which was insufficient to reach the shock deformation regime. Thus, using computational simulations to estimate the structure behaviour at high strain rates was necessary. Experimental and computational results showed that all ACS structures exhibit a nominal stress–strain relationship typical for cellular materials. As the loading conditions shifted to a dynamic regime, the micro–inertia effect became increasingly pronounced, leading to a corresponding rise in structure stiffness. The Poisson's ratio in all ACS increases gradually, making them superior to traditional cellular materials, which experience a sudden increase in Poisson's ratio during loading. Additionally, the study found that the structures exhibited a rise in the auxetic effect with an increase in strain rate, highlighting the benefits of axisymmetric structures in high-loading regimes. Overall, the obtained results provide valuable insights into the mechanical properties of ACS under different loading regimes and will contribute to further design improvements and the fabrication of novel ACS metamaterials.
Keywords: axisymmetric chiral structure, auxetic, chiral unit cell, impact testing, dynamic characterisation, finite element simulations
Published in DKUM: 15.02.2024; Views: 345; Downloads: 31
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Abstract: This study investigated the high-strain rate mechanical properties of open-cell aluminium foam M-pore®. While previous research has examined the response of this type of foam under quasi-static and transitional dynamic loading conditions, there is a lack of knowledge about its behaviour under higher strain rates (transitional and shock loading regimes). To address this gap in understanding, cylindrical open-cell foam specimens were tested using a modified Direct Impact Hopkinson Bar (DIHB) apparatus over a wide range of strain rates, up to 93 m/s. The results showed a strong dependency of the foam's behaviour on the loading rate, with increased plateau stress and changes in deformation front formation and propagation at higher strain rates. The internal structure of the specimens was examined using X-ray micro-computed tomography (mCT). The mCT images were used to build simplified 3D numerical models of analysed aluminium foam specimens that were used in computational simulations of their behaviour under all experimentally tested loading regimes using LS-DYNA software. The overall agreement between the experimental and computational results was good enough to validate the built numerical models capable of correctly simulating the mechanical response of analysed aluminium foam at different loading rates.
Keywords: Open-cell aluminium foam, Micro-computed tomography, High-strain rate, Direct impact hopkinson bar, Digital image correlation, Computer simulation
Published in DKUM: 06.12.2023; Views: 428; Downloads: 42
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Abstract: V diplomskem delu je opisana nadgradnja Split Hopkinson Pressure Bar (SHPB) preizkuševališča z motoriziranim sistemom za pozicioniranje dveh hitrih kamer. Kameri dodata raziskavi karakteristik materialov nov vir podatkov in način analiziranja le teh. Kameri se delita na horizontalno in vertikalno. Vsaka kamera bo imela svoj motoriziran sistem, ki bo zmožen krmilja po vseh treh koordinatah v prostoru. Sistem za horizontalno kamero je že bil razvit na Czech Technical University v Pragi in ga je potrebno prilagoditi za SHPB v Mariboru. Vertikalni del je potrebno na novo skonstruirati. Oba motorizirana sistema bosta za nosilne dele uporabljala lahke aluminijast profile. Za krmilje pa bodo uporabljena kroglična vretena in okrogla vodila skupaj s pripadajočimi krogličnimi maticami in linearnimi krogličnimi ležaji. Horizontalni in vertikalni motoriziran sistem bo možno upravljati posamezno ali skupaj kot celoto.
Keywords: Split Hopkinson Pressure Bar, hitra kamera, krmilje, konstruiranje, linearno vodilo, kroglično vreteno
Published in DKUM: 24.09.2020; Views: 1086; Downloads: 81
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Abstract: Namen diplomske naloge je umeriti model sublimacijskega sušenja tako, da se bodo dobljeni rezultati čim bolj ujemali z eksperimentalnimi rezultati. Za izdelavo naloge smo izvedli več simulacij, ki ponazarjajo potek realnega sušenja. Umerjanje smo izvedli na podlagi dobljenih rezultatov. Vsaka sprememba parametra vpliva na rezultat, vendar se vplivi parametrov med seboj nekoliko razlikujejo. Ugotovili smo, da na potek simulacije najbolj vpliva parameter robni pogoj. Ob spremembi sevalnega robnega pogoja so odstopanja največja. Vsem konstantam v robnih pogojih smo določili nove vrednosti, kar je pripomoglo k večjemu ujemanju z eksperimentalnim potekom sublimacijskega sušenja.
Keywords: liofilizacija, sublimacija, sušenje z zamrzovanjem, prenos toplote, prenos snovi
Published in DKUM: 15.09.2016; Views: 3937; Downloads: 282
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