1. |
2. 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
 Link to full text |
3. 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
Link to full text |
4. 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
Link to full text |
5. 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
Link to full text |
6. Thermal post-impact behaviour of closed-cell cellular structures with fillersMatej Vesenjak, Andreas Öchsner, Zoran Ren, 2007, original scientific article Abstract: The study describes the behavior of regular closed-cell cellular structure with gaseous fillers under impact conditions and consequent post-impact thermal conduction due to the compression of filler gas. Two dependent but different analyses types have been carried out for this purpose: (i) a strongly coupled fluid-structure interaction and (ii) a weakly coupled thermal- structural analysis. This paper describes the structural analyses of the closed-cell cellular structure under impact loading. The explicit code LS-DYNA was used to computationally determine the behavior of cellular structure under compressive dynamic loading, where one unit volume element of the cellular structure has been discretised with finite elements considering a simultaneous strongly coupled interaction with the gaseous pore filler. Closed-cell cellular structures with different relative densities and initial pore pressures have been considered. Computational simulations have shown that the gaseous filler influences the mechanical behavior of cellular structure regarding the loading type, relative density and type of the base material. It was determined that the filler's temperature significantly increases due to the compressive impact loading, which might influence the macroscopic behavior of the cellular structure.
Keywords: mechanics, cellular structures, closed cells, gas fillers, impact loading, fluid-structure interaction, dynamic loads, LS-DYNA, ANSYS CFX 10.0, computational simulations
Published in DKUM: 31.05.2012; Views: 1851; Downloads: 37
Link to full text |
