• Journal of Korea Foundry Society
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• v.40 no.3
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• pp.61-65
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• 2020

Rheo-diecasting with stirring has been used in many material industries. As the 4th Industrial Revolution approaches the world, eco-friendly high-strength and light-weight materials become more important. Casting methods have been studied and used for aluminum-alloy automobile parts. This study carried out the effect analysis of the micro-structure and mechanical properties, such as yield/ultimate tensile strength, elongation, and hardness, of A356 using the 6-pole EMS (electro-magnetic stirring) casting process with a high electromagnetic force. As a result, the hardness and elongation of the A356 after T6 heat-treatment show a significant improvement, respectively, by 20% and 50%.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.667-674
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• 1992

Recently advantages in composite and light weight material technique have led to the increased use of structural adhesives in various industries. In spite of such wide application of the adhesive joints, the evaluation method of fracture strength and design methodology of them, have not been established. In this study finite element method, theoretical and experimental analyses were investigated according to changes of lap length and adhesive for adhesive single-lap joint. As the results, the strength evaluation of adhesive joint by conventional nominal stress, was pointed out inadequate strength evaluation and design method regardless stress singularity, stress distribution and crack propagation in its adhesive layer. Also, it was examined the problems to apply fracture mechanics by means of static and fatigue test.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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• pp.2502-2512
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• 2000

Truss structures are widely used in many space structures, such as large antenna systems, space stations, precision segmented telescopes because they are light in weight and amenable in assembly or deployment. But, due to the low damping capacity, they remain excited for a long time once disturbed. These structural vibrations can reduce life of the structures and cause unstable dynamic characteristics. In this research, vibration suppression experiment has carried out with a three-dimensional 15-member truss structure using two piezoelectric actuators. Piezoelectric actuators which consist of stacks of thin piezoelectric material disks are directly inserted to the truss structure collocated with the strain sensors. Each actuator is controlled digitally in decentralized manner, based on local integral and proportional feedback. The optimal positions of the actuators are determined by the modal damping ratio and the control force. Numerical simulation has carried out to determine optimal position of each actuator.

• Clean Technology
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• v.23 no.3
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• pp.325-330
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• 2017

This study presents the preparation of n-tetradecane-in-water emulsions with different weight ratios of n-tetradecane and water, and their potential application in packaging and shipping vaccines. The size and distribution of the n-tetradecane droplets are characterized using optical microscopy and light scattering methods, respectively. The thermal properties of the emulsions are determined using the T-history method. In the results, the emulsions, which are comprised of 17 ~ 30 wt% oil, 3 wt% surfactant, and 67 ~ 80 wt% water, are stable and have droplet sizes in the range of 100 to 800 nm. The thermal properties demonstrate that subcooling is prevented through increasing the droplet size. The results indicate that the n-tetradecane/water emulsions containing 25 ~ 35 wt% n-tetradecane, with a melting point of $2{\sim}8^{\circ}C$ and a latent heat of $227.0{\sim}250.8kJ\;kg^{-1}$, are good candidate materials for packaging and shipping vaccines.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.39 no.5
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• pp.52-57
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• 2007

Corrugated fiberboard is a representative packaging material because of high compressive strength and stiffness in spite of light weight. The flutes of corrugated fiberboard are various depending on the height and the number per unit length of flute. The corrugated fiberboard with microflute like E, F or G with low height less than 1.5 mm has developed. Because it has some advantages including higher stiffness and lower requirement of fiber than carton board, it has a possibility to replace folding box board. Its consumption has been increased with the various applications like graphic packaging. As microflute has the different geometry from other conventional flutes, it can show the different behavior in testing and it may require a new testing method. In this study, we evaluated the edgewise compressive strength of the corrugated fiberboard with microflute according to ISO and other standard test methods. And the effect of specimen shape and platen compression rate was examined. From this study, we found that ISO methods was suitable and reasonable methods for corrugated fiberboard with microflute.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.386.1-386.1
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• 2014

The ionic polymer-metal composite (IPMC), a type of electro-active polymer material, has received enormous interest in various fields such as robotics, medical sensors, artificial muscles because it has many advantages of flexibility, light weight, high displacement, and low voltage activation, compare to traditional mechanical actuators. Mostly noble metal materials such as gold or platinum were used to form the electrode of an IPMC by using electroless plating process. Furthermore, carbon-based materials, which are carbon nanotube (CNT) and reduced graphene-CNT composite, were used to alter the electrode of IPMC. To form the electrode of IPMC, we employ the synthesized graphene on copper foil by chemical vapor deposition method and use the transfer process by using a support of PET/silicone film. The properties of graphene were evaluated by Raman spectroscopy, UV/Vis spectroscopy, and 4-point probe. The structure and surface of IPMC were analyzed via field emission scanning electron microscope. The fabricated IPMC performance such as displacement and operating frequency was measured in underwater.

• Korean Journal of Materials Research
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• v.9 no.7
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• pp.715-723
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• 1999

Magnesium has been used as wheel materials in the automotive industry for more than 20 years. The magnesium wheels, which are lighter by 25% than aluminum wheels, provide easy controllability providing excellent road holding by the reduction of weight. The purpose of this work is to develop cast AZ91D alloy wheel by sand cast and permanent mold cast. The fluxless melting with the protective gas $(SF_6+CO_2)$ was Performed to eliminate oxidation of melt and impurity. The transfer of molten magnesium to the mold was done by using gas-pressurized Pump system through the heated pipe. The mechanical properites of AZ91D alloy wheel were investigated as a function of heat treatment, ingot composition.

• Composites Research
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• v.28 no.2
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• pp.52-57
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• 2015

Soft morphing robotics making use of smart material and based on biomimetic principles are capable of continuous locomotion in harmony with its environment. Since these robots do not use traditional mechanical components, they can be built to be light weight and capable of a diverse range of locomotion. This paper illustrates a flexible smart phone robot made of smart soft composite (SSC) with inchworm-like locomotion capable of two-way linear motion. Since rigid components are embedded within the robot, bending actuators with embedded rigid segments were investigated in order to obtain the maximum bending curvature. To verify the results, a simple mechanical model of this actuator was built and compared with experimental data. After that, the flexible robot was implemented as part of a smart phone robot where the rigid components of the phone were embedded within the matrix. Then, experiments were conducted to test the smart phone robot actuation force under different deflections to verify its load carrying capability. After that, the communication between the smart phone and robot controller was implemented and a corresponding phone application was developed. The locomotion of the smart phone robot actuated through an independent controller was also tested.

• Journal of the Korean Wood Science and Technology
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• v.26 no.1
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• pp.70-75
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• 1998

In this paper, the relationships between volumetric mixing ratio of rubber chip and physical and mechanical properties of wood/rubber composite panel was examined in order to investigate the mixture characteristics of wood and rubber chip. Because of the specific gravity of rubber differed from wood chip, physical properties of wood/rubber composite panel was shown very different values by mixing rate of chip element. Specific gravity in air-dry of composite panel was increased rapidly as volumetric percent of rubber chip was increased. Moisture content of composite panel was decreased as volumetric percent of rubber chip element was increased. This results was considered that wood weight is light and porosity material for moisture absorption. Compressive strength and modulus of rupture in bending test were decreased as volumetric percent of rubber chip increased. By mixing ratio control of chip elements, various wood/rubber composite panel can be applicable to every interior materials such as subfloor, playground, and exterior materials such as road blocks for recreational facilities in garden and forest and city parks.

• Transactions of Materials Processing
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• v.17 no.1
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• pp.13-18
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• 2008

Mg and Mg alloys are promising materials for light weight high strength applications. In this paper, grain refinement of pure Mg using severe plastic deformation was tried to enhance the mechanical properties of the hard-to-deform metallic material. The microstructure and the mechanical properties of Mg processed by equal channel angular pressing(ECAP) at various processing temperatures were investigated experimentally. ECAP with channel angle of $90^{\circ}$ and corner angle of $0^{\circ}$ was successful at $300^{\circ}C$ without fracture of the samples during the processing. The hardness of the ECAP processed Mg decreased with increasing ECAP processing temperature. The effect of temperature on the hardness and microstructure of the ECAP processed Mg were explained by the dislocation glide in the basal plane and non-basal slip systems and by the dynamic recrystallization and recovery.