• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1663-1666
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• 2007

The finite element method is applied to analyze the deformation mechanisms in the closed-cell Al foam under the compression. The modeling of the real cellular structure proceeds with the concept of the reverse engineering. First of all, the small, $10{\times}\;10{\times}\;10mm^3$ sized specimens of the closed-cell Al foam are prepared. The micro focus X-ray CTsystem of SHIMADZU Corp. is used to scan the full structures of the specimens. The scanned structures are converted to the geometric surfaces and solids through the software for 3-D scan data processing, RapidFormTMof INUS Tech. Inc. Then the solid meshes are directly generated on the converted geometric solids for the finite element analysis. The large elastic-plastic deformation and 3-D contact problems for the Al cellular material are considered. The clear and successful analysis for the deformation mechanisms in the closed-cell Al foam is carried out through the comparison of the numerical results in this research with the referred experimental ones.

• Journal of Powder Materials
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• v.19 no.4
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• pp.278-284
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• 2012

$Al_2O_3$ foam is an important engineering material because of its exceptional high-temperature stability, low thermal conductivity, good wear resistance, and stability in hostile chemical environment. In this work, $Al_2O_3$ foams were designed to control the microstructure, porosity, and cell size by varying different parameters such as the amount of amphiphile, solid loading, and stirring speed. Particle stabilized direct foaming technique was used and the $Al_2O_3$ particles were partially hydrophobized upon the adsorption of valeric acid on particles surface. The foam stability was drastically improved when these particles were irreversibly adsorbed at the air/water interface. However, there is still considerable ambiguity with regard to the effect of process parameters on the microstructure of particle-stabilized foam. In this study, the $Al_2O_3$ foam with open and closed-cell structure, cell size ranging from $20{\mu}m$ to $300{\mu}m$ having single strut wall and porosity from 75% to 93% were successfully fabricated by sintering at $1600^{\circ}C$ for 2 h in air.

• Journal of Mechanical Science and Technology
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• v.20 no.6
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• pp.819-827
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• 2006

The stress-strain relation of aluminum (Al) alloy foam cell wall was evaluated by the instrumented sharp indentation method. The indentation in a few micron ranges was performed on the cell wall of Al-alloy foam having a composition or Al-3wt.%Si-2wt.%Cu-2wt.%Mg as well as its precursor (material prior to foaming). To extract the stress-stram relation in terms of yield stress ${\sigma}_y$, strain hardening exponent n and elastic modulus E, the closed-form dimensionless relationships between load-indentation depth curve and elasto-plastic property were used. The tensile properties of precursor material of Al-alloy foam were also measured independently by uni-axial tensile test. In order to verify the validity of the extracted stress-strain relation, it was compared with the results of tensile test and finite element (FE) analysis. A modified cubic-spherical lattice model was proposed to analyze the compressive behavior of the Al-alloy foam. The material parameters extracted by the instrumented nanoindentation method allowed the model to predict the compressive behavior of the Al-alloy foam accurately.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.10
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• pp.1686-1694
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• 2003

The foam-filled tube beams can be used for the front rail and firewall structures to absorb impact energy during frontal or side collision of vehicles. In the case of side collision where bending is involved in the crushing mechanism, the foam filler would be effective in maintaining progressive crushing of the thin-walled structures so that much impact energy could be absorbed. In this study, bending behaviors of the closed-cell-aluminum-alloy-foam-filled stainless steel tube were investigated. The various foam-filled specimens including piecewise fillers were prepared and tested. The aluminum-alloy-foam filling offered the significant increase of bending resistance. Their suppression of the inward fold formation at the compression flange as well as the multiple propagating folds led to the increase of load carrying capacity of specimens. Moreover, the piecewise foams would provide the easier way to fill the thin-walled shell structures without the drawback of strength.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.179-182
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• 2007

The compressive fatigue tests on the closed cell Al-Si-Ca alloy foams with two different thicknesses were performed using a load ratio of 0.1. The quasi-static and cyclic compressive behaviors were obtained respectively. The fatigue stress-life (S-N) curves were evaluated from the obtained cyclic compressive behaviors. S-N curves were presented for the onset of progressive shortening. It turned out that the fatigue strength showed higher value for the thicker foam and the onset of shortening of thinner foam took place earlier. The crushing was found to initiate in a single band which broadens gradually with additional fatigue cycles. Progressive shortening of the specimen took place due to a combination of low cycle fatigue failure and cyclic ratcheting.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.289-292
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• 2001

Aluminium foams, having a closed cell structure, fabricated by applying the powder compact method and an induction heating were studied. The powdered A6061 mixed with the powdered titanium hydride as a foaming agent was hot pressed into a foamable precursor. The resulting precursor was foamed by induction heating up to desired temperature. The effects of the titanium hydride content ($0.3{\~}1.5 wt.\%$), pressing pressure of the foamable precursor material (50-150kN), the forming temperature ($610{\~}690^{\circ}C$) and heating rate during foaming on the expansion behavior of the foam were investigated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.890-893
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• 2002

This study is focused to predict the behavior of Al foam with closed-cell structure during the 3 point bending test and the upsetting test according to aspect ratio. We calculated characters of aluminum foams with closed-cell structure and took the simulation. The effects on the aspect ratio of the cell was investigated parametrically. The analysis was carried out on two models, First, the bending test in elasticity of the rectangular beam, and Second, the upsetting test in plasticity of the circular cylinder. In the analysis, the deformation of the beam and the cylinder was influenced by the aspect ratio of the cell. Further, We assumed that the geometry of feared aluminum cell change the stress and strain in the test.

• Korean Journal of Materials Research
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• v.22 no.6
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• pp.309-315
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• 2012

Metal foam has many excellent properties, such as light weight, incombustibility, good thermal insulation, sound absorption, energy absorption, and environmental friendliness. It has two types of macrostructure, a closed-cell foam with sealed pores and an open-cell foam with open pores. The open-cell foam has a complex macrostructure consisting of an interconnected network. It can be exploited as a degradable biomaterial and a heat exchanger material. In this paper, open cell Mg alloy foams have been produced by infiltrating molten Mg alloy into porous pre-forms, where granules facilitate porous material. The granules have suitable strength and excellent thermal stability. They are also inexpensive and easily move out from open-cell foamed Mg-Al alloy materials. When the melt casting process used an inert gas, the molten magnesium igniting is resolved easily. The effects of the preheating temperature of the filler particle mould, negative pressure, and granule size on the fluidity of the open cell Mg alloy foam were investigated. With the increased infiltration pressure, preheat temperature and granule sizes during casting process, the molten AZ31 alloy was high fluidity. The optimum casting temperature, preheating temperature of the filler particle mould, and negative pressure were $750^{\circ}C$, $400-500^{\circ}C$, and 5000-6000 Pa, respectively, At these conditions the AZ31 alloy had good fluidity and castability with the longest infiltration length, fewer defects, and a uniform pore structure.

• Transactions of Materials Processing
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• v.12 no.5
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• pp.449-456
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• 2003

Multi-step induction heating process was applied to the powder compact melting technique as a new heating process to achieve pinpoint accuracy, faster cycle time, repeatability, non-contact and energy-efficient heat in a minimal amount of time. The objective of this study is the establishment of the input data diagram of multi step induction heating process for automation of the fabrication process of 6061 Al foams with desired density. At first, proper induction coil was designed to obtain a uniform temperature distribution over the entire cross sectional area of specimen. By using this coil, foaming experiments were performed to investigate the multi-step induction heating conditions such as capacity, temperature and time conditions of each heating and holding step. On the basis of the obtained multi-step induction heating conditions, relationship between final heating temperature and fraction of porosity was investigated.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.190-195
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• 2004

The compression-compression fatigue properties of the closed cell Al-Si-Ca alloy foams have been studied. The monotonic and cyclic compressive properties were compared with each other and the fatigue stress-life (S-N) curves were presented. In compression-compression fatigue, the crushing was found to initiate in a single band which broadens gradually with additional fatigue cycles. Progressive shortening of the specimen took place due to a combination of low cycle fatigue failure and cyclic ratcheting which is in accordance with the findings of previous researchers [1-3]. Young's modulus of the foam was found to decrease with the increasing strain in case of fatigue test however in case of monotonic compression test the value of Young's modulus increased with the strain (number of cycles). The endurance limit on the basis of $10^{7}$ cycles obtained by extrapolating the experimental results were 0.98 MPa and 1.70 MPa for load ratios 0.1 and 0.5 respectively which are 34 % and 59 % of the plateau stress.