• Steel and Composite Structures
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• v.21 no.5
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• pp.1145-1156
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• 2016

To study the effects of foam core density and face-sheet thickness on the mechanical properties and failure modes of aluminum foam sandwich (AFS) beam, especially when the aluminum foam core is made in aluminum alloy and the face sheet thickness is less than 1.5 mm, three-point bending tests were investigated experimentally by using WDW-50E electronic universal tensile testing machine. Load-displacement curves were recorded to understand the mechanical response and photographs were taken to capture the deformation process of the composite structures. Results demonstrated that when foam core was combined with face-sheet thickness of 0.8 mm, its carrying capacity improved with the increase of core density. But when the thickness of face-sheet increased from 0.8 mm to 1.2 mm, result was opposite. For AFS with the same core density, their carrying capacity increased with the face-sheet thickness, but failure modes of thin face-sheet AFS were completely different from the thick face-sheet AFS. There were three failure modes in the present research: yield damage of both core and bottom face-sheet (Failure mode I), yield damage of foam core (Failure mode II), debonding between the adhesive interface (Failure mode III).

• Steel and Composite Structures
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• v.39 no.3
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• pp.229-241
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• 2021

This work focused on aluminum foam sandwich (AFS) with different foam core densities and different face-sheet thicknesses subjected to constant amplitude three-point bending cyclic loading to study its fatigue performance. The experiments were conducted out by a high frequency fatigue test machine named GPS-100. The experimental results showed that the fatigue life of AFS decreased with the increasing loading level and the structure was sensitive to cyclic loading, especially when the loading level was under 20%. S-N curves of nine groups of AFS specimens were obtained and the fatigue life of AFS followed three-parameter lognormal distribution well. AFS under low cyclic loading showed pronounced cyclic hardening and the static strength after fatigue test increased. For the same loading level, effects of foam core density and face-sheet thickness on the fatigue life of AFS structure were trade-off and for the same loading value, the fatigue life of AFS increased with aluminum foam core density or face-sheet thickness monotonously. Core shear was the main failure mode in the present study.

• Steel and Composite Structures
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• v.29 no.3
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• pp.301-308
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• 2018

Properties of AFS vary with the changes in the face-sheet materials. Hence, the performance of AFS can be optimized by selecting face-sheet materials. In this work, three types of face-sheet materials representing elastic-perfectly plastic, elastic-plastic strain hardening and purely elastic materials were employed to study their effects on the flexural behavior and failure mechanism of AFS systematically. Result showed face-sheet materials affected the failure mechanism and energy absorption ability of AFS significantly. When the foam cores were sandwiched by aluminum alloy 6061, the AFS failed by face-sheet yielding and crack without collapse of the foam core, there was no clear plastic platform in the Load-Displacement curve. When the foam cores were sandwiched by stainless steel 304 and carbon fiber fabric, there were no face-sheet crack and the sandwich structure failed by core shear and collapse, plastic platform appeared. Energy absorption abilities of steel and carbon fiber reinforced AFS were much higher than aluminum alloy reinforced one. Carbon fiber was suggested as the best choice for AFS for its light weight and high performance. The versus strength ratio of face sheet to core was suggested to be a significant value for AFS structure design which may determine the failure mechanism of a certain AFS structure.

• Steel and Composite Structures
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• v.25 no.3
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• pp.327-335
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• 2017

To gain more knowledge of aluminum foam sandwich structure and promote the engineering application, aluminum foam sandwich consisting of 7050 matrix aluminum foam core and 304 stainless steel face-sheets was studied under three-point bending by WDW-T100 electronic universal tensile testing machine in this work. Results showed that when aluminum foam core was reinforced by 304 steel face-sheets, its load carrying capacity improved dramatically. The maximum load of AFS in three-point bending increased with the foam core density or face-sheet thickness monotonically. And also when foam core was reinforced by 304 steel panels, the energy absorption ability of foam came into play effectively. There was a clear plastic platform in the load-displacement curve of AFS in three-point bending. No crack of 304 steel happened in the present tests. Two collapse modes appeared, mode A comprised plastic hinge formation at the mid-span of the sandwich beam, with shear yielding of the core. Mode B consisted of plastic hinge formation both at mid-span and at the outer supports.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.149-158
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• 2004

In most RP processes, the inherent stair-stepped surfaces and shrinkage-induced warping of the parts require post processing such as surface finishing. To minimize such defects, VLH-ST, a newly developed RP process, employs a 3.9-mm thick expandable polystyrene (EPS) foam sheet and a hot wire to contour it to have slant linear-interpolated sides. The use of relatively thick sheets for layers, however, limits the process capability of constructing fine details, especially smaller than the layer thickness. This study is focused on the development of a post processing method fo fine details of VLM-ST parts. The post-processing tool was designed to meet all the requirements for the desirable post processing. It adopted a hot wire as a means of melting the EPS foam sheet. Various basic experiments on the post processing were carried out to obtain the optimal process conditions. The dominant process parameters such as the radiated heat input, the tool speed, and the gap between the tool tip and the foam sheet (tool height) were considered in the experiments. The effectiveness of the developed post-processing method fo forming or engraving fine details on the VLM-ST parts has been thus demonstrated. The experiments on engraving several sets of letters, such as CANESM, 인간, and 한국과학기술원, on the EPS foam sheet were carried out. In addition, a flowery shape was engraved on a three-dimensionally curved surface of a pottery-shape VLM-ST part.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.5
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• pp.603-608
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• 2010

In this study, one type of circular shaped composite tube was used, combined with reinforcing foam and without foam. Furthermore, CFRP(Carbon Fiber Reinforced Plastic) circular member manufactured from CFRP prepreg sheet for lightweight design. CFRP is an anisotropic material which is the most widely adapted lightweight structural member. The crashworthy behavior of circular composite material tubes subjected to static axial compression under same conditions is reported in this paper. Test was executed in order to compare the results to the energy absorption and collapse shape. The collapse mode during the failure process were observed and analyzed. The behavior of polymeric foams to the tubes crashworthiness were also investigated. According to the experimental results, specimens filled with foam are higher total energy absorption than the other specimens not filled with the foam.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.47 no.2
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• pp.42-52
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• 2015

In this study, cellulose nanofibrils (CNF) were modified through carboxymethylation or TEMPO-mediated oxidation and their effects on ionicity and characteristics of sheet, film, and foam were investigated. Carboxymethylation was carried out on pulp fibers as a pre-treatment before preparation of CNF. The gel-like and translucent CNF hydrogel was obtained by grinding of carboxymethylated cellulose fibers. Carboxymethylated CNF film and freeze dried sheet showed higher transparency than that of untreated CNF. The CNF sheet with high strength and the CNF foam without large ice crystals were obtained by using the carboxymethylated CNF. TEMPO-mediated oxidation was carried out as a post-treatment of CNF. The zeta potential and charge demand of TEMPO-oxidized CNF were increased with an increase in oxidation time and addition amount of NaClO. The density of sheet made of TEMPO oxidized CNF was increased with the amount of oxidizing agent. The TEMPO oxidized cellulose nanofiber (TOCN) which was obtained from supernatant after centrifugation could be converted to transparent film.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.1
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• pp.11-23
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• 2010

A sacrificial member with aluminum foam of excellent energy absorption capacity was proposed for the protection of significant structures. Parametric studies of explicit finite element analyses were performed to investigate the pressure mitigation of close-range air-blasts. The scaled distance of the blast had a range of Z=0.48~0.95 and an empirical blast load function was utilized. The analytical parameters of the aluminum foam were density, thickness and the existence of a cover sheet. Analytical results showed that the transmitted pressure can be controlled to have a similar level of yield values of the foam by using a foam with low density and higher thickness. As the blast load increased, the sacrificial member needed to have higher density and thickness. A cover sheet of the foam clearly showed its effect on the wider distribution of blast pressure. It is necessary to determine the design parameters of sacrificial foams considering different energy dissipation capacities according to the scaled distance.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.3
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• pp.41-46
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• 2007

Lightweight multi-layered boards with high stiffness for the automotive interior trims were developed, which were composed of a single material. The boards were constructed in the form of substrate/core/substrate with newly developed materials. The materials which have high tensile strength and elongation were selected for the substrate materials, and those which have high compressive strength and low density were selected for the core materials. 25 types of multi-layered boards were fabricated using the selected substrate and core materials. The compatibility with the skin materials, the formability and the tensile strength and flexural strength of the specimens were evaluated. The results show that three types of multi-layered boards(Kenboard/EPP foam/Kenboard, Twintex/PP honeycomb/Twintex, Curv sheet/EPP foam/Curv sheet) are appropriate for the automotive interior trims. Considering the ease of materials supply and the economical aspect, Kenboard/EPP foam/Kenboard is thought to be the most realistic alternative.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.759-762
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• 2000

Rapid Prototyping (RP) techniques have their unique characteristics according to the working principles: stair-stepped surface of parts due to layer-by-layer stacking, low build speed caused by line-by-line solidification to build one layer, and additional post processing to improve surface roughness, so it is required very high cost to introduce and to maintain RP apparatus. The objective of this study is to develop and design a new RP process, Variable Lamination Manufacturing using expandable polystyrene foam sheet as part material (VLM-S), which can make up for the disadvantage of existing techniques, and to develop an apparatus to implement the process. In order to examine the possibility of practical utilization of the proposed VLM-S process for prototyping of a general three-dimensional shape, an auto-shift lever knob and a pyramid shape were fabricated.