• Transactions of Materials Processing
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• v.21 no.8
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• pp.493-498
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• 2012

A wheel nut wrench is one of the hand tools used to loosen and tighten lug nuts on automobile wheels and it has generally a solid-type geometry for commercial vehicles. However, the solid-type wheel nut wrenches manufactured by hot forging processes exhibit several drawbacks such as heavy weight and rough surface finish. Thus, many efforts have been devoted to change the part geometry and improve the manufacturing process. For this purpose, the weight of the final product can be reduced drastically using a hollow tube as the initial stock, which can be manufactured by the more economical manufacturing process of cold forging. In this study, the cold forging of a hollow-type wheel nut wrench for commercial vehicles was designed based on the results of fundamental experiments and CAE analyses using the commercial finite element code DEFORM-3D. In addition, cold forging experiments were conducted on a special-purpose forming machine for hollow wheel nut wrenches in order to validate the designed process sequence. As results, it was found that the final products with a weight reduction of 39% and better surface appearance can be manufactured without any defect with the newly designed cold forging process.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.261-264
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• 2010

Dual Pulse Rocket Motor is a solid rocket motor with two grains separated by a bulkhead and rupture disc. The elasto-plastic explicit dynamic analysis of rupture disc was conducted by the finite element method. The effect of the slit geometry of rupture disc with radial slit was parametrically analyzed in terms of rupture time and shape. The results can be used to control the rupture pressure by changing the slit geometry of rupture disc.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.105-112
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• 2010

Dual Pulse Rocket Motor is a solid rocket motor with two grains separated by a bulkhead and rupture disc. The elasto-plastic explicit dynamic analysis of rupture disc was conducted by finite element method. The effect of the slit geometry of a rupture disc was analyzed for rupture time and shape by the parametric study. The results can be used to control the rupture pressure by the change the slit geometry of a rupture disc.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.8
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• pp.3295-3300
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• 2012

Three Dimensional finite element method (FEM) was used to obtain the stress intensity factor for subsurface cracks and surface cracks existing in inhomogeneous materials. A geometry model, i.e. a solid containing one or several 3D cracks is defined. Several distributions of local node density are chosen, and then automatically superposed on one another over the geometry model. Nodes are generated by the bubble packing, and ten-noded quadratic tetrahedral solid elements are generated by the Delaunay triangulation techniques. To examine accuracy and efficiency of the present system, the stress intensity factor for a semi-elliptical surface crack in a plate subjected to uniform tension is calculated, and compared with Raju-Newman's solutions. Then the system is applied to analyze interaction effects of two dissimilar semi-elliptical cracks in a plate subjected to uniform tension.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1995.11a
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• pp.11-30
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• 1995

The ignition characteristics of a reactive solid with rough surface by constant heat flux were studied. The geometry of surface was represented by a set of identical protrusions having a shape of wedge based on the block of reactive solid. Several regimes of ignition were found, depending on the ratio of the protrusion length and the depth of the heated layer, formed in course of ignition process: 1) when the substance is ignited as the massive block, and the effect of roughness is not pronounced; 2) when ignited are the individual protrusions; and 3) in the intermediate region between the first two. Critical ignition conditions: ignition time and ignition criterion, are determined for the three regimes. The results are compared with the results for the one-dimensional ignition of the semi-infinite body. It is shown, that the effect of geometry on ignition results in the considerable reduction of ignition delay, and the amount of energy required for the successful ignition is less compared to the one- dimensional case.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1740-1745
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• 2004

A simplified resistor network model for electrical and mass transport in anode-supported planar solid oxide fuel cell (SOFC) was constructed in order to investigate the effect of interconnect rib geometry on the cell performance. For accurate potential calculation, activation and concentration over-potentials at the electrode/electrolyte interfaces were fully considered in this calculation. When contact resistance was not considered, the optimum interconnect rib length were calculated to be $0.1{\sim}0.2$ mm for 2 mm half unit cell for given operation conditions and properties. However, with realistic contact resistance, the interconnect rib length should be increased to provide larger contact area and thus to obtain better performance.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.10a
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• pp.185-190
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• 2000

Die design by computer simulation has some advantages compared with the conventional method which has performed by designer's experiences and trials and errors. The die filling and solidification process of thixoforming process were simulated by MAGMAsoft/thixo module. First of all, thixoforming die design was applied to previously geometry shape. The value of pressure distribution shows high and uniform as the gate diameter is 18mm. Designed gating system considering the deformation of die and product was suggested by the filling simulation. Gate velocity(7.25m/s) of designed gating system shows that propriety to semi-solid metal working process and CAE results were in good agreement with experimental results.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.226-230
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• 1997

A plasticity theory applicable to powdered metal compaction is briefly summarized and its variational form for the finite element analysis is described. The compaction processes of axisymmetric solid cylinder are simulated. For the analysis of the friction effect of solid cylinder, the investigations were performed for different compact geometries. Highlights of the results for given geometries are reported in terms of transmitted pressure on the lower punch from the upper punch through the compact and maximum density variation within the compacts. General conclusions from these simulation results are : (1) the friction coefficient could be selected from the transmitted force data during the single acting compaction test with the simulated results ; and (2) density variatioins within the compacts are very much dependent of the compact geometry such as the height to diameter ratio and the frictional condition between compact and dies.

• Clean Technology
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• v.11 no.4
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• pp.181-188
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• 2005

Developed is the new gas-solid flow ball valve where air injection purging concept is applied for the control and the reduction of particle fouling. CFD analyses are conducted for investigating the interaction between gas-sold and air injection streams and the fouling phenomena in valve, and the analysis results are reflected in the design of valve geometry and air injection condition. Through the actual tests on designed ball valve, the present valve is shown to be superior in fouling reduction.

• Journal of the Korean Ceramic Society
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• v.52 no.5
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• pp.356-360
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• 2015

The specific role of current collectors was investigated at the electrolyte/electrode interface of solid oxide fuel cells (SOFCs). Ag grids were fabricated as current collectors using electrohydrodynamic (EHD) jet printing for precise control of the grid geometry. The Ag grids reduced both the ohmic and polarization resistances as the pitch of the Ag grids decreased from $400{\mu}m$ to $100{\mu}m$. The effective electron distribution along the Ag grids improved the charge transport and transfer at the interface, extending the active reaction sites. Our results demonstrate the applicability of EHD jet printing to the fabrication of efficient current collectors for performance enhancement of SOFCs.