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: 11
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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: 29
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3. From stochastic foam to designed structure: balancing cost and performance of cellular metalsDirk Lehmhus, Matej Vesenjak, Sven De Schampheleire, Thomas Fiedler, 2017, review article Keywords: cellular metal, metallic foam, metal foam, porous materials, lattice materials, costs, manufacturing, additive manufacturing, mechanical properties, energy absorption
Published in DKUM: 04.09.2017; Views: 1649; Downloads: 649
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4. HEAT TRANSFER IN UNIPORE CELLULAR STRUCTUREMatevž Frajnkovič, 2017, master's thesis Abstract: This master’s thesis deals with heat transfer in a specific cellular structure, called UniPore cellular structure. Said structure has been developed at Japan’s Kumamoto university. The structure is manufactured using the technique of explosion welding. Due to longitudinal orientation of the pores and high thermal conductivity of materials, the thermal properties of the structure as a heat exchanger have been analysed. Influence of different boundary conditions on the effectiveness of heat transfer in the structure has been analysed. The results are compared and analysed. It has been concluded, that the structure itself might be suitable when dealing with dirty liquids. Usage of the structure in such systems would enable a quick and efficient cleaning process of the waste, that deposits on the walls over time.
Keywords: Heat transfer, cellular structure, porous materials, CFD
Published in DKUM: 24.08.2017; Views: 1824; Downloads: 212
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5. Computational simulations of unidirectional cellular material unipore subjected to dynamic loadingMatej Vesenjak, Kazuyuki Hokamoto, Zoran Ren, 2012, published scientific conference contribution Abstract: Cellular structures have an attractive combination of mechanical properties and are increasingly used in modern engineering applications. Consequently, the research of their behaviour under quasi-static and dynamic loading is valuable for engineering applications such as those related to strain energy absorption. The paper focuses on behaviour of a newly developed cellular structure UniPore with unidirectional pores under dynamic loading. The computational model of the cellular structure was based on realistic (reconstructed) irregular geometry of the manufactured specimens and analysed using the code LS-DYNA. The mechanical properties have been investigated by means of parametric computational simulations considering various material and geometrical parameters. Additionally, the influence of the gaseous pore filler influence has been considered using fully coupled computational models. Furthermore, with computational simulations also the influence of the anisotropy has been evaluated.
Keywords: cellular materials, computational model, UniPore
Published in DKUM: 10.07.2015; Views: 903; Downloads: 36
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6. Heat conduction in closed-cell cellular metalsMatej Vesenjak, Zoran Žunič, Andreas Öchsner, Matjaž Hriberšek, Zoran Ren, 2005, original scientific article Abstract: The purpose of this research was to describe the thermal transport properties in closed-cell cellular metals. Influence of cell size variations with different pore gases has been investigated with transient computational simulations. Heat conduction through the base material and gas in pores (cavities) was considered, while the convection and radiation were neglected in the initial stage of this research. First, parametric analysis for definingthe proper mesh density and time step were carried out. Then, two-dimensional computational models of the cellular structure, consisting of the base material and the pore gas, have been solved using ANSYS CFX software within the framework of finite volume elements. The results have confirmed theexpectations that the majority of heat is being transferred through the metallic base material with almost negligible heat conduction through the gas in pores. The heat conduction in closed-cell cellular metals is therefore extremely depended on the relative density but almost insensitive regarding tothe gas inside the pore, unless the relative density is very low.
Keywords: heat transfer, cellular metal materials, porous materials, closed cells, gas fillers, computational simulations
Published in DKUM: 01.06.2012; Views: 2314; Downloads: 104
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7. Characterization of open-cell cellular material structures with pore fillersMatej Vesenjak, Andreas Öchsner, Zoran Ren, 2008, original scientific article Abstract: Due to their mechanical properties, cellular material structures are often used in automotive, aerospace, ship and railway industries, as elements for deformational energy absorption. New advanced cellular material structures have been evaluated and characterised in the scope of this study in order to determine their energy absorption capability through the deformation process. Parametric computational simulations in the framework of the finite element method have been used for this purpose. Newly developed computational models of regular open-cell cellular material structures considering viscous pore fillers have been developed and their response under impact conditions was analysed using the explicit code LS-DYNA. The results of the performed study show that introduction of viscous fillers indeed increases the energy absorption capability of open-cellular material structures. Additionally, it was determined that the size of the cellular material (number of cells) dramatically influences the cellular structure response and that the filler influence is stronger in cellular structures with higher relative density.
Keywords: cellular materials, computer simulation, deformation, mechanical properties
Published in DKUM: 31.05.2012; Views: 1751; Downloads: 84
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9. Behaviour of cellular materials under impact loadingMatej Vesenjak, Zoran Ren, Andreas Öchsner, 2008, original scientific article Abstract: The paper describes experimental and computational testing of regular open-cell cellular structures behaviour under impact loading. Open-cell cellular specimens made of aluminium alloy and polymer were experimentally tested under quasi-static and dynamic compressive loading in order to evaluate the failure conditions and the strain rate sensitivity. Additionally, specimens with viscous fillers have been tested to determine the increase of the energy absorption due to filler effects. The tests have shown that brittle behaviour of the cellular structure due to sudden rupture of intercellular walls observed in quasi-static and dynamic tests is reduced by introduction of viscous filler, while at the same time the energy absorption is increased. The influence of fluid filler on open-cell cellular material behaviour under impact loading was further investigated with parametric computational simulations, where fully coupled interaction between the base material and the pore filler was considered. The explicit nonlinear finite element code LS-DYNA was used for this purpose. Different failure criteria were evaluated to simulate the collapsing of intercellular walls and the failure mechanism of cellular structures in general. The new computational models and presented procedures enable determination of the optimal geometric and material parameters of cellular materials with viscous fillers for individual application demands. For example, the cellular structure stiffness and impact energy absorption through controlled deformation can be easily adapted to improve the efficiency of crash absorbers.
Keywords: mechanics, porous materials, cellular materials, impact loading, mechanical testing, fluid-structure interaction, failure mechanism
Published in DKUM: 31.05.2012; Views: 1923; Downloads: 89
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10. Evaluation of thermal and mechanical filler gas influence on honeycomb structures behaviourMatej Vesenjak, Andreas Öchsner, Zoran Ren, 2007, original scientific article Abstract: In this paper the behavior of hexagonal honeycombs under dynamic in-plane loading is described. Additionally, the presence and influence of the filler gas inside the honeycomb cells is considered. Such structures are subjected to very large deformation during an impact, where the filler gas might strongly affect their behavior and the capability of deformational energy absorption, especially at very low relative densities. The purpose of this research was therefore to evaluate the influence of filler gas on the macroscopic cellular structure behavior under dynamic uniaxial loading conditions by means of computational simulations. The LS-DYNA code has been used for this purpose, where a fully coupled interaction between the honeycomb structure and the filler gas was simulated. Different relative densities, initial pore pressures and strain rates have been considered. The computational results clearly show the influence of the filler gas on the macroscopic behavior of analyzed honeycomb structures. Because of very large deformation of the cellular structure, the gas inside the cells is also enormously compressed which results in very high gas temperatures and contributes to increased crash energy absorption capability. The evaluated results are valuable for further research considering also the heat transfer in honeycomb structures and for investigations of variation of the base material mechanical properties due to increased gas temperatures under impact loading conditions.
Keywords: mechanics, cellular materials, honeycomb structure, gas filler, thermal properties, mechanical properties, dynamic loading, LS-DYNA, computational simulations
Published in DKUM: 31.05.2012; Views: 2094; Downloads: 73
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