• 오토저널
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• 제12권1호
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• pp.40-48
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• 1990

Bake hardenability of batch annealed steel sheets is investigated in connection with the amount of tensile deformation and the bake hardening condition. This study associates with the method for producing bake hardening materials by means of batch annealing process and for measuring bake hardenability which is not yet fully established. The experimental result demonstrates the relationship between strain distribution and bake hardening behavior in various bake hardening conditions, which provides an essential information for automobile design and related sheet metal forming in a press shop. The result also shows the bake hardenability of the tested material increases as the baking temperature is increased from 150.deg. C. The result assures the bake hardening materials can guarantee reasonably high strength as well as good uniformity in yield strength for the automobile body by sheet metal forming process.

• 한국자동차공학회논문집
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• 제8권3호
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• pp.151-162
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• 2000

This study is concerned with computerized multi-level substructuring methods and stress analysis of coil springs. The purpose of substructuring methods is to reduce computing time and capacity of computer memory by multiple level reduction of the degrees of freedom in large size problems that are modeled by three dimensional continuum finite elements. In this paper, the spring super element developed is investigated with tension, torsion, and bending of a cylindrical bar in order to verify its accuracy and efficiency for the multi-level substructuring method. And then the algorithm is applied to finite element analysis of coil springs. The result demonstrates the validity of the multi-level substructuring method and the efficiency in computing time and memory by providing good computational results in coil spring analysis.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 정기총회 및 창립40주년기념 학술대회 학회본부
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• pp.197-199
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• 1987

This paper is investigated on characteristics of photoresist using inorganic a-$Se_{75}Ge_{25}$. The sensitivity of negative photoresist showing insolubility against alkalie solution, with Ag-photodoped, is more prominent than that of positive photoresist used with only a-$Se_{75}Ge_{25}$. It is also showed that the contrast of negative photoresist, ${\gamma}=2.9$, is more prominent than that of positive photoresist, ${\gamma}=1.4$.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 추계학술대회 논문집
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• pp.55-63
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• 1994

The analysis of superplastic sheet forming process is studied by the use of the finite element method using a convected coordinate system and a skew boundary condition. In the formulation, the large inelastic behavior of the superplastic material is described as incompressible, nonlinear, viscous flow. The formulation is then approximated to the finite dimensional space with the use of membrane elements, which results in algebraic linear equations. In addition to the finite element formulation, a pressure cycle control algorithm is combined in the analysis for optimization of the forming time, which deals with the maximization of the strain rate sensitivity, the protection of the thickness reduction, the consistency of the desired strain rate and improvement of formability.

• 소성∙가공
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• 제12권4호
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• pp.401-407
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• 2003

This paper newly proposes a mesh regularization method for the enhancement of the efficiency in sheet metal forming analysis. The regularization method searches for distorted elements with appropriate searching criteria and constructs patches including the elements to be modified. Each patch is then extended to a three-dimensional surface in order to obtain the information of the continuous coordinates. In constructing the surface enclosing each patch, NURBS(Non-Uniform Rational B-Spline) surface is employed to describe a three-dimensional free surface. On the basis of the constructed surface, each node is properly arranged to form unit elements as close as to a square. The state variables calculated from its original mesh geometry are mapped into the new mesh geometry for the next stage or incremental step of a forming analysis. The analysis results with the proposed method are compared to the results from the direct forming analysis without mesh regularization in order to confirm the validity of the method.

• 소성∙가공
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• 제12권4호
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• pp.320-327
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• 2003

This paper is concerned with forming analysis of Front Side Members and effects of the forming analysis on crash analysis of an auto-body. For efficient forming analysis, equivalent draw-bead restraining forces are calculated with ABAQUS/Standard and then used as the boundary condition in forming simulation. In order to demonstrate the validity of the forming analysis, the thickness variation in the numerical simulation result is compared quantitatively with the one in the real product. Forming histories obtained kom the forming analysis are utilized as the initial condition of the crash analysis for accurate assessment of the crashworthiness. Crashworthiness such as the load-carrying capacity, crash mode and the energy absorption is evaluated and investigated for the identification of forming effects.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.286-289
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• 2009

This paper deals with the experimental investigation of the steel cord straightening during the stranding process. The over-twisting and roller straightening process are essential to improve the product quality during the stranding process. To investigate the effectiveness of two processes, four experimental cases are constructed according to the use of an over-twister and two roller straighteners. Three assessment items, such as the residual torsion, the arc-height and the preforming ratio, are measured in each experimental case for the quantitative evaluation of a steel cord. The steel cord shape is also measured to investigate the variation of the straightness efficiently after passing through each process. Finally, the effectiveness of the over-twisting and the roller straightening process is explained based on the experimental results.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.21-24
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• 2007

This paper deals with introduction of testing equipments for the evaluation of dynamic tensile characteristics of auto-body steel sheets and the crashworthiness of auto-body members. The servo-hydraulic high speed material testing machine was developed for tensile tests at the intermediate strain rate to obtain the tensile material properties at the strain rate under 500/sec. The split Hopkinson bar apparatus using the elastic wave was developed for dynamic material characteristics at the high strain rate ranged from 1,000 to 10,000/sec. The servo-hydraulic high speed crash testing machine is the equipment for the evaluation of the collapse load and crashworthiness of auto-body members. High speed carrying truck crashes to specimen with the maximum velocity of 17 m/sec.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.348-351
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• 2007

Simulations of the buckling behavior of a single wall carbon nanotube(SWCNT) was carried out using molecular dynamics simulation. Molecular dynamics simulations were done with 1fs of time step. Tersoff's potential function was used as the interatomic potential function since it has been proved to be reliable to describe the C-C bonds in carbon nanotubes. Compressive force was applied by moving the top end of the nanotube at a constant velocity. Buckling behavior under compressive load was observed for (15,15) armchair SWCNTs with 2nm of diameter and 24.9nm of length. Buckling load and critical strain is obtained from the MD simulation. Deformation occurred on the top region of the CNT because of fast downward velocity.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.352-355
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• 2007

Polycrystalline materials such as steels(BCC) and aluminum alloys(FCC) show the strain hardening and the strain rate hardening during the plastic deformation. The strain hardening is induced by deformation resistance of dislocation glide on some crystallographic systems and increase of the dislocation density on grain boundaries or inner grain. However, the phenomenon of the strain rate hardening is not demonstrated distinctly. In this paper, tensile tests for various strain rates are performed in the rage of $10^{-2}$ to $10^2s^{-1}$ then, specimens are extracted on the same strain position to investigate the microscopic behavior of deformed materials. The extracted specimen is investigated by using the electron backscattered diffraction(EBSD) and transmission electron microscopy(TEM) results which contain grain size, grain shape, aspect ratio and dislocation substructure.