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1.
Thermal post-impact behaviour of closed-cell cellular structures with fillers
Matej 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: 31.05.2012; Views: 892; Downloads: 16
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2.
Evaluation of thermal and mechanical filler gas influence on honeycomb structures behaviour
Matej 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: 31.05.2012; Views: 1037; Downloads: 20
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3.
Heat conduction in closed-cell cellular metals
Matej 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: 01.06.2012; Views: 1322; Downloads: 64
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4.
Computational model for the analysis of bending fatigue in gears
Janez Kramberger, Matjaž Šraml, Srečko Glodež, Jože Flašker, Iztok Potrč, 2004, original scientific article

Abstract: A computational model for the determination of service life of gears with regard to bending fatigue in a gear tooth root is presented. The fatigue process leading to tooth breakage is divided into crack initiation (Ni) and crack propagation (Np) periods, where the complete service life is defined as N = Ni + Np. The strain-life method in the framework of the FEM method has been used to determine the number of stress cycles Ni required for fatigue crack initiation. Gear tooth crack propagation was simulated using a FEM method based computer program which uses principles of linear elastic fracture mechanics. The Paris equation is then used for the further simulation of the fatigue crack growth. The presented model is used to determine the service life of a real spur gear made from through-hardened steel 42CrMo4.
Keywords: machine elements, gears, bending fatigue, service life, fatigue crack initiation, fatigue crack propagation, computational simulations, numerical modelling, fracture mechanics
Published: 01.06.2012; Views: 2219; Downloads: 60
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