• Transactions of Materials Processing
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• v.18 no.3
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• pp.236-244
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• 2009

In response to growing environmental and collision-safety concerns, the automotive industry has gradually used high-strength and ultla-high-strength steels to reduce the weight of automobiles. In order to overcome inherent process disadvantages of these materials such as poor formability and high springback at room temperature, hot forming has recently been developed and adopted to produce some important structural parts in automobiles. This method enables manufacturing of components with complex geometric shapes with minimal springback. In addition, a quenching process may enhance the material strength by more than two times. This paper investigates mechanical and forming characteristics of high-strength boron-alloyed steel with hot forming, in terms of hardness, microstructure, residual stress, and springback. In order to compare with experimental results, a finite element analysis of hot forming process coupled with phase transformation and heat transfer was carried out using DEFORM-3D V6.1 and also, to predict high temperature mechanical properties and flow curves for different phases, a material properties modeler, JMatPro was used.

• International Journal of Advanced Culture Technology
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• v.8 no.1
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• pp.62-70
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• 2020

As an effective means of price discrimination, some suppliers offer trade credit to the distributors in order to stimulate the demand for the product they produce. The availability of the delay in payments from the supplier enables discount of the distributor's selling price from a wider range of the price option in anticipation of increased customer's demand. Since the distributor's lot-size is affected by the demand for the customer, the distributor's lot-size and the selling price determination problem is interdependent and must be solved at the same time. Also, in many common business transactions, the distributor pays the shipping cost for the order and hence, the distributor's ordering cost consists of a fixed ordering cost and the shipping cost that depend on the order quantity. In this regard, we deal with the joint lot-size and price determination problem when the supplier allows delay in payments for an order of a product. The positive effects of credit transactions can be integrated into the EOQ (economic order quantity) model through the consideration of retailing situations, where the customer's demand is a function of the distributor's selling price. It is also assumed that the distributor's order cost consists of a fixed ordering cost and the variable shipping cost. We formulate the distributor's mathematical model from which the solution algorithm is derived based on properties of an optimal solution. A numerical example is presented to illustrate the algorithm developed.

• Korean Journal of Materials Research
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• v.5 no.2
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• pp.191-196
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• 1995

Self-bonding strength developed at the interface of amorphous PEEK films is highly sensitive to the processing variables(time, temperature, and pressure) during the bonding process. In order to examine the effects of these processing variables, amorphous PEEK films were bonded at various bonding conditions and the resultant interfacial bond strengths were measured using a modified single lap-shear test. Experimental results showed that the developed self-bonding strength increases with increase in bonding temperature and is directly proportional to the bonding time raised to the 1/4 power. The applied pressure seems only to produce better wetting at the beginning stage of the bonding process. Conclusively, the self-bonding of amorphous PEEK films provides a great potential for developing excellent bond strength approaching the strength of the parent material without any adhesives in structural applications.

• The Journal of Engineering Research
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• v.2 no.1
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• pp.133-138
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• 1997

The conventional process in synthesizing mullite powder required high temperature ($1300^{\circ}C$) and long chemical reaction time. Thus the combustion process was used to synthesize the mullite powder in order to reduce the reaction time and temperature. The mixture of metal nitrate, fine silica, and fuel was used as the redox compounds under various experimental conditions. The combustion fire in hot plate experiment in rich, lean and stoichiometry fuel does not produce mullite. However, the obvious mullite, small amount of alumina and cristobalite was observed in the $500^{\circ}C$ pre-heat treatment furnace experiment. The components such as silica, urea, aluminm nitrate should be stoichiometry in order to make a perfect mullite crystal.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.455-458
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• 2009

In this research, the effect of Sc on the micro structure and mechanical properties of Al-20Si alloy powders and their extruded bar was investigated. The Al-20wt%Si and Al-20wt%Si-0.6wr%Sc powders were produced by gas atomization. The micro structures of the alloy powders and extrude was examined by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The alloy powders were subsequently canned, degassed and extruded in order to produce the alloy bulk. It was found that the micro structure of the Al-20Si alloy powder was refined and the mechanical properties was significantly improved by the addition of 0.6Sc.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.197-198
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• 2002

In order to produce micromachined parts with a great dimensional accuracy, it is important to clarify the influence of heterogeneity and/or discontinuity of workpiece materials on the micromachining process, because almost all structural materials are composed of heterogeneous and/or homogeneous crystal grains at the micro scale. Experiments where JIS S25C steel had been scratched with a diamond triangular pyramid indenter were conducted under a field emission scanning electron microscope (FE-SEM). The difference of plastic deformation at a groove scratched between a pearlite zone and a proeutectoid ferrite zone was investigated through comparison with the groove scratched of a pearlite zone and a proeutectoid ferrite zone.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.14-17
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• 2003

Vibration control of a composite plate with a surface-bonded fiber Bragg grating (FBG) sensor and piezoceramic actuators has been performed using a neural network based adaptive predictive control algorithm. For the detection of Bragg wavelength changes, two cavity lengths in Fabry-Perot read-out interferometers are used in order to produce two quadrature phase shifted signals. The FBG sensor system and real-time neuro-adaptive control algorithm could be applicable to diverse dynamic systems.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.1504-1507
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• 2009

In this paper, the etching behavior of ZnO in $CF_4$ plasma mixed Ar was investigated. Previously, the etch rate in $CF_4$/Ar plasma was reported that it is slower than that in Cl containing plasma. But, plasma included Cl atom can produce the by-product such as $ZnCl_2$. In order to solve this film contamination, no Cl containing etching gas is required. We controlled the etching parameter such as source power, substrate bias power, and $CF_4$/Ar gas ratio to acquire the fast etch rate using a ICP etcher. We accomplished the etching rate of 144.85 nm/min with the substrate bias power of 200W. As the energetic fluorine atoms were bonded with Zinc atoms, the fluoride zinc crystal ($ZnF_2$) was observed by X-ray photoelectron spectroscopy (XPS).

• English Language & Literature Teaching
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• v.12 no.4
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• pp.253-276
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• 2006

The purpose of this study is to compare and analyze the aspects of task-based materials in high school English textbooks for first year students in Korea. Based on the theoretical backgrounds for designing communicative tasks and the basic contents of the 7th national curriculum for English, a total of six different qualitative evaluation categories of task-based materials are constructed. The six categories include input data, settings, activity types, language skills, activity themes, and communicative functions. The results of the data analysis showed that the regulations of the 7th national English curriculum, which were aimed at improving the students' communicative abilities, were properly reflected in the materials of task-based activities of all textbooks. On the other hand, a few problems were found in some textbooks: too many individual tasks; being out of proportion in presenting task types and themes; non-systematic introduction of language skills, etc. To conclude, a few suggestions are made to provide some meaningful considerations for the text material developers in order to produce better textbooks in the future: task goals and rationale that encourage the learner's positive motivation; authenticity of input data based on the real-world context; a collaborative learning environment that enhances communicative interaction; a proportional representation of the various activity types including creative problem-solving procedures; systematic introduction of integrated language skills, etc.

• Journal of Mechanical Science and Technology
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• v.20 no.11
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• pp.1920-1933
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• 2006

Piezoelectric materials produce an electric field by deformation, and deform when subjected to an electric field. The coupling nature of piezoelectric materials has acquired wide applications in electric-mechanical and electric devices, including electric-mechanical actuators, sensors and structures. In this paper, a hollow sphere composed of a radially polarized spherically anisotropic piezoelectric material, e.g., PZT_5 or (Pb) (CoW) $TiO_3$ under internal or external uniform pressure and a constant potential difference between its inner and outer surfaces or combination of these loadings has been studied. Electrodes attached to the inner and outer surfaces of the sphere induce the potential difference. The governing equilibrium equations in radially polarized form are shown to reduce to a coupled system of second-order ordinary differential equations for the radial displacement and electric potential field. These differential equations are solved analytically for seven different sets of boundary conditions. The stress and the electric potential distributions in the sphere are discussed in detail for two piezoceramics, namely PZT _5 and (Pb) (CoW) $TiO_3$. It is shown that the hoop stresses in hollow sphere composed of these materials can be made virtually uniform across the thickness of the sphere by applying an appropriate set of boundary conditions.